An Ichneumon wasp - Amblyteles armatorius

I am an amateur naturalist trying to learn something about everything living in my garden.

Hello! After a goodly absence I am back with some more of my garden wildlife. I hope there may be one or two of you out there still reading. Certainly my garden has not run short of new lifeforms to offer. Despite over a 100-species blogged so far, I have a long backlog of additional finds with more turning up all the time.

Photo 1 shows a magnificent insect I spotted resting on my hedge in late-summer of last year. The body was around a cm in length. Based on some similar images on the web I'm identifying it as an Ichneumon wasp - Amblyteles armatorius.


With tens-of-thousands of species of Ichneumon wasp worldwide and about 3200 in Britain alone, definitively identifying Ichneumons is a job for the specialist. Dr Gavin Broad is one such and has helpfully made available an online British checklist and a key to the sub-families of Ichneumonidae. You can download the entire 380-odd pages of the 1903-published Ichneumonologia Brittanica for free here. For any naturalist willing to grapple with the subject however, a supreme example of what can be achieved (and surely a candidate for "all-time greatest garden study") is given by Jennifer Owen. Her book, The Ecology of a Garden (Cambridge Uni. Press) records 15 years of painstaking cataloguing of the wildlife in a UK garden. During her studies Dr Owen discovered no fewer than 529 species of Ichneumon of which 15 were new to Britain and a staggering 4 were new to science!

From the comments above it will be understood my amateur's identification, based on a photograph alone, of my wasp as A. armatorius is to be treated with caution. It is certainly not the only European black -and-yellow striped Ichneumon as can be seen, for example, from the photo's here of species such as Ichneumon stramentor, I. xanthorius, Eutanyacra crispatoria and Diphyus quadripunctarius. For now I'm sticking with A. armatorius, as some of these others have yellow-striped antennae and other small differences, but I'm happy to be corrected by any of the experts out there.

Sadly, I have been able to uncover rather few details of the natural history of my Ichneumon. I have learnt that it is fairly common in the UK and the sole species in the genus Amblyteles. Adults apparently feed on pollen, that of umbellifers being a common target. In common with many other ichneumon's, the larvae are parasites of caterpillars, one target moth being The Yellow Underwing (Noctua pronuba). The larvae hatch inside the caterpillar and devour it from the inside. Other target moth species besides the Yellow Underwing are variously stated for A. armatorius. The scientific paper by Rolf Hinz (Entomofauna, 6(8), 1985, pp.73-77) disputes these claims however.

The paper above is in German incidentally, which is unfortunate if like me, you don't speak the language! (I found a free online copy of this paper some time ago, but have entirely failed to relocate it since. Anyone?). Since this was one of the very few learned articles I came across on A. armatorius however, I was determined not to be put off and came up with the idea of running the German text through Google's free, online automatic translation service. The results of computer translation are not always transparent. A German sentence that, in the original, I take to say something along the lines:
"I'm grateful to Messrs. G. and E. MannBausch Heidt of the Künanz Upland Bird-research Centre for supplying me with specimens"
gets translated as
"Messrs. G. and E. Mann Bausch Heidt from the research Künanz bird-house in the mountain, the procurement of the material allowed, thanks."
Nevertheless, with patience it's generally possible to get the gist and I'll certainly consider using this approach in future.

I appear to have digressed! When starting today's posting it had been my intention to say something on the amusing topic of the religious debate sparked amongst Victorians naturalisists by the life-style of the Ichneumonidae. Since I have written enough for now however, and since, with another 3000-odd British Ichneumonidae out there, I feel confident I will have other chances to revisit this fascinating family of insects in the future, I will leave my somewhat cryptic last sentence hanging in the air and bid you farewell for now.

Two Prominent Moths

I am an amateur naturalist trying to identify everything living in my garden.

Some time ago I blogged the moth trap I was constructing. My first design was only partially successful (most of my catch were escaping!) and since then my designs have undergo a number of iterations to finally arrive at The Walloon Super Trap you see before you in photo 1! I'm pleased with this design. In fact, the only problem is that the few times I've put it out in my garden it has yielded such a bumper catch of night-time insects I now have a long backlog awaiting a write up on this blog.

Anyway, on to the stars of today's posting. Photos 1 and 2 show two moths trapped (for the record) on 25th and 22nd April 2009 respectively (I let them go after I'd taken their photos).

A little time spent with my copy of Field Guide to Moths (Waring, Townsend) and I was able to identify the first as a Lesser Swallow Prominent (Pheosia gnoma) and the second as a Coxcomb Prominent (Ptilodon capucina). I'm guessing the various points and fluffy quiffs on my moths are there to resemble thorns and to break up the moths' outline when resting on branches.

The Lesser Swallow Prominent is superficially similar in appearance to the Swallow Prominent (Pheosia tremula) but the neat white triangle on the upper part of the wing identifies my moth as the former. The caterpillars feed on Birch and the book tells me it is fairly common in the UK.

The Coxcomb is also common. Its larvae feed on a variety of trees including birch, hazel and hawthorn.

My moths are both members of the Notodontidae family of moths of which 27 species have been recorded in Britain (there are several thousand worldwide). My attempts to learn something of them led me to some fascinating online papers about the sense of hearing in moths.

It turns out the Notodontidae moths are notable for having some of the simplest ears of any insect. To we humans, insects wear their ears in rather strange positions - sometimes on the legs, sometimes the thorax and even (in the case of some lacewings) on the wings. This paper by Yager gives a review.

Insect ears broadly follow a common design. A thin membranous 'ear drum' (the tympanal membrane) vibrates in response to sound and the vibrations are detected by structures called scolopidia that are basically stretch receptors. The scolpidia detect movements of the membrane and fire off signals down a connecting nerve. Some grasshoppers have around 2,000 scolopidia. Notodontid moths are at the other extreme with only one.

Yager's paper above quotes the remarkable figure of 1 Angstrom (=a ten-millionth of a millimetre) as the smallest vibration of the membrane that insect ears can detect. If true, I find this truely incredible as 1 Angstrom is about the diameter of a single atom!

I did not manage to find any freely available references to the hearing specifically of my moths, but I have come close with a paper by Annemarie Skurlykke on the hearing of the Swallow Prominent (you'll recall my moth above is the Lesser Swallow Prominent). From this I learn that the Swallow Prominent hears best at frequencies around 60kHz. For perspective, the highest note an adult human can hear is said typically to be around 20kHz. Why should moths be sensitive to such high ('ultrasonic') frequencies? The answer can be summed up succinctly: Bats! Bats are prodigious predators of night flying insects and hunt by echolocation using ultrasound.

I came across a couple of interesting online review articles (by Ratcliffe et.al. and another by Miller and Surlykke) describing how moths and other insects react to hearing an approaching moth. It seems that many moths react in two stages. If the bat is some distance away the moth simply flies away from the sound of the echolocating bat. If the bat gets close enough to strike however, the moth takes more dramatic action such as spiralling in flight or even folding its wings and dropping out of the air. How moths are able to determine the range of the bat isn't fully understood. Bats reduce the time between their ultrasonic squeaks as they get near to striking an insect however in order to better 'see' their prey, and the suggestion is that the moths are sensitive to this increase in squeak-rate. Regardless of how they do it the defence seems fairly successful with those species of moth capable of hearing and reacting to bats improve their survival chances by some 40%.

Of course moths do not get everything their own way. Firstly, diving to the ground is fine...unless (as Guigon and Fullard explain) the 'ground' turns out to be water! Naturally also the bats are not about to take things lying down and have evolved a number of strategies to bypass the moths' defences. Some appear to have adopted frequencies above or below the range of moths' hearing and others may rely to a significant extent on simply seeing (visually) or listening for their prey. Ultimately however, as Miller and Surlykke comment "some barbastelle bats prey almost exclusively on tympanate moths, and just how they do this is not known". Another of nature's puzzles!

A signalling fly Poecilobothrus nobilitatus

I am an amateur naturalist trying to learn something about everything living in my garden.

I have a plastic tub in my garden that has become partly filled with rainwater. Passing it last summer, my attention was caught by some flies busying themselves at the water's edge. A closer look revealed some fascinating behaviour: the wings of my flies were characteristically marked and the flies were solemnly raising and lowering them just as might an airport worker guiding a plane to a parking spot with a pair of semaphore flags.

I took some photo's though I confess I rather expected to fail to identify my fly. There are so many species (more than 15,000 in Europe) that to identify an unknown fly can be a tall order unless you're willing to spend hours with a magnifying glass and have access to some serious, specialist literature. Fortunately however, it turned out my fly is not uncommon, its behaviour having been noted by a fair few people, and an internet search led me to the species name: Poecilobothrus nobilitatus.

The stately wing-spreading displays of my fly are part its courtship display. As everyone knows, courtship displays are very widespread in the animal kingdom and can be fantastically intricate (one need only think of peacocks or the dance of Great Crested Grebes (video here)) . It's very natural to wonder what purpose such displays serve. Vast amounts of literature exist on this topic, with a great many unknowns and disputed theories. I don't have anything like the knowledge to comment expertly. My blog is about my learning something of my garden's natural history however, so a few facts gathered from some general reading on my part seem in order:

According to my copy of An Introduction to Behavioural Ecology (Krebs and Davies), the modern view is that, at the deepest level, courtship arises from a conflict between males and females over scarce resources. The point is that sperm are small and energetically 'cheap' to produce. Eggs, however, are larger and energetically more costly to produce and gestate. In the jargon, eggs are a scarce resource. Since eggs are, in this sense 'expensive, high value objects' it is worth males investing effort and energy competing for them. Equally, for females it pays to be 'choosy' when it comes to 'cashing in' the energy investment an egg represents.

The argument above might seem rather abstract, but its consequences are deep. Take the issue of mating with a wrong species: Some species of fruit flies for example, can and sometimes do, interbreed. Often this inter-species breeding results in sterile offspring however. From the perspective above, such parents have wasted precious time and energy. Clearly, it would have benefited them to have had some way to accurately check a prospective partner's species prior to mating. The elaborate courtship dances of some fly species (see here for example) may be just this: a way for females to check whether a male is of the correct species. From the female viewpoint, this avoids wasted energy on improper fertilization of her 'expensive' eggs. From the male point of view, although dancing costs him some energy, eggs are a scarce resource and having found some (i.e. a fertile female) it is worth the investment.

To take a second instance: Since eggs are a scarce resource it is important to lay them somewhere safe and where there is enough food available for the hatchlings. Some courtship displays - such as those where a male presents a female with some 'gift' (say, a morsel of food or a beak-full of nesting material) may be a way for the sexes to share the energetic cost of laying in a particular location (the female pays the cost of depositing her precious eggs; the male pays the cost of finding and presenting a 'courtship gift' that proves the location's suitability).

Yet another purpose of a courtship display may for females to test whether a male is a fit, strong individual, and able to pass on good genes to the egg. Actually, one needs to be a little careful before asserting a given courtship display is about a male demonstrating genetic fitness. To see why, imagine a species of bird that shows-off some glossy plumage during courtship. To say the male is demonstrating genetic fitness, makes an assumption that there exists an (inheritable) gene for glossy plumage for that bird. There may be, but on the other hand there may not. It could be that a male's glossy feathers are nothing to do with his genes but are due to him having been living somewhere that allowed him a good a plentiful food supply. The fact that females are choosing glossy feathers may be nothing (or perhaps only indirectly) to do with a male's genes, but because they say: "Food here is plentiful. It's a good place to breed". The point is not that advertising 'good genes' can never be a reason for a courtship display, simply that one cannot take it for granted as an explanation.

Anyway, in summary, a modern view is that courtship is about competition for resources between males and females. The successful male gets the benefit of the female's energy investment in eggs. In return females get an energy expenditure (=courtship display) from a male that relays something of benefit such as 'this is a good place to lay', or 'the male before you is the correct species', or 'the male before you has 'good' genes', or...(there are lots of other scenarios).

This barely makes a dent on a vast subject of course, and a great deal more could be written on the theory of courtship. This isn't the place to do it however, and instead let's get back to talking specifically about the my fly P. nobilitatus:

The best freely available online paper about my fly I came across was that of Zimmer, Diestelhorst and Lunau which describes the courtship behaviours of eight, so-called 'long legged flies' (Dolichopodidae), mine included. A number of these flies carry display 'badges' they use in courtship. Liancalus virens for example, also has signalling spots on its wings (see picture here). Neurigona quadrifasciata (here) uses foot markings to signal to females.

The paper provides a number of interesting facts about my fly. Firstly, experiments show that male wing span is directly proportional to body size: males with a big thorax also have big wing spans. During courtship P. nobilitatus males work to keep at a constant distance of 2.5cm from females. Taking these facts together, a plausible hypothesis is that female P. nobilitatus flies consider male body size important (as an indicator of a male's health status perhaps). By this argument the male's wing badges and constant- separation-dance are present in order to help females accurately estimate the body size of their suitor by sight.

Another intriguing suggestion in the paper is that males may have evolved signalling 'badges' to allow them to mate on the ground. The idea is this: some species of flies court in flight with males performing aerial stunts or hovering. Presumably these difficult and energetic winged manoeuvres may again allow females to assess health by looking at, say, wingspan. Now, suppose a male could 'con' a female's reproductive senses into thinking she was being presented with a hovering male when in fact both were sat firmly on the ground?! This is not as implausible as it sounds when we remember we are talking about a little fly whose intelligence and eyesight are not necessarily great! The female's reproductive senses may detect the 'beating' wings of a hovering male simply by whether her eyes detect (say) the outline of a wing and certain patterns of light and dark in the space before her. If a male could replicate these patterns whilst still on the ground, he might be able to fool the female's senses into a mating response, and at the same time save himself from the energetically costly business of hovering. The technical term for such cheating is 'sexual mimicry'. The paper concedes that this idea remains unproven for the long legged flies. I hope you'll agree however it's fascinating stuff and it all goes to show just how incredibly rich and intricate are the patterns of life just outside our front doors.

Lady's Smock Cardamine pratensis

I am an amateur naturalist trying to learn something about everything living in my garden.

Photo 1 shows an attractive flower I found growing wild in a neglected corner of my garden early last summer.

A little time spent with my trusty copy of The Wildflower Key (Francis Rose) and I'm fairly confident my plant is Lady's Smock. The leaves of my plant are also rather characteristic (photo 2) with the lower leaves tending towards round with the largest leaf being the one furthest from the stem, whilst the upper leaves are rather long and narrow.

My copy of The Englishman's Flora (Geoffrey Grigson) lists around thirty alternative common names for Lady's Smock from the pretty Cuckoo Bread, Cuckoo flower, Lucy Locket and Milking Maids to the less flattering Pig's Eyes and Bog Spink!

The scientific name for my flower is Cardamine pratensis. Pratensis is from the Latin 'of meadows'. From some web searching I understand Cardamine owes its heritage to the anicent Greek physician Dioscorides (ca. 50AD) who used the name for some cress-like plants, karda being Greek for 'heart', and damao to 'tame or overpower'. (I've read that Lady's Smock is an edible, spicy, salad leaf, though I can't vouch for the truth of this.)

Lady's Smock is a favoured food of the caterpillars of the Orange Tip butterfly.

C. pratensis is a perennial, native to the British Isles and is highly variable. The paper here gives a flavour of the lengths the professionals have gone to in attempting to characterise it. My copy of New Flora of the British Isles (Stace) sums things up rather bluntly however as "impossible to subdivide usefully; identity of [named] variants [...] is very dubious". My attempt to get some basic amateur understanding of the issue led me into a study of polyploidy. I'm certainly no expert on genetics but briefly my understanding is this:

As most people know, at times the DNA inside living cells gets packaged into structural units, the chromosomes. A microscope reveals we have 46 chromosomes. Closer investigation reveals that these 46 are in fact present as two largely similar sets of 23 i.e. 23 chromosomes from our mother and a similar 23 from our father. (The phrase 'largely similar' skips over a wealth of detail, such as the fact that a certain chromosome from our mother might carry a different characteristic, say eye colour, to that from our father etc. - but never mind that here) . For humans we say "2n=46". Other mammals have other chromosome counts, for example I read variously on the web that the kangaroo has a mere 2n=12 whilst the European hedgehog boasts 2n=88 (in general there is no link between chromosome number and the size or complexity of a creature).

In the case of many plants, a lesser number of insects, amphibians, fish and a very few mammals (one being an Argentinian Plains Rat - see the parade of polyploids here!) however, things are more complicated. Some varieties of strawberry for example contain not, as we humans, two largely similar sets of 23 chromosomes but no fewer than eight sets of seven chromosomes. This gets written as "8x=56". This condition of having more than two sets of chromosomes is termed polyploidy.

The fact that more than 30% of plants go in for polyploidy would seem to indicate it must have some important benefits. There are many theories as to what these benfits might be. It's been suggested for example, that polyploidy may promote greater variation in a species and thereby help it evolve ('radiate') more easily into new environments, or that polyploidy may provide protection against 'in-breeding' issues that might otherwise arise for plants that self-fertilise. It seems also that some polyploids are healthier and more vigorous than non-polyploids. In all however, there seems to be no universally accepted theory of why so many plants are polyploids. Another of nature's mysteries!

Anyway, all of this preamble basically allows me to comment that my garden weed occurs in a bewildering variety of genetic 'forms' from the 'diploid' 2n(=2x)=16 through types with chromosomes numbers of 14, 15, 16, 19, 20, 21 – 28, 30, 32, 37, 42, 44, 45 and 48.

After the science, who better to have the last word than the Bard. From the song 'Spring' at the end of Love's Labour's Lost:

When daisies pied and violets blue,
And lady-smocks all silver white,
And cuckoo-buds of yellow hue
Do paint the meadows with delight,

Painted Lady Butterfly Vanessa (Cynthia) cardui

I am an amateur naturalist trying to learn something about everything living in my garden.

Photo 1, taken back in late Summer, shows a Painted Lady butterfly enjoying a well-earned rest on a leaf in my garden. I say 'well earned' as this butterfly will likely have undergone an amazing 1000 mile migration, to arrive in my garden from North Africa.

The entire British population of Painted Ladies (Ladys?) arrives here in Spring and leaves again in Autumn (strictly not all leave, but those that don't fail to survive the British winter).

To have encountered a Painted Lady in my garden last Summer is perhaps unremarkable when you learn that 2009 was a mass migration year for Painted Ladies to the UK. Millions arrived, with one flutter (the collective noun for butterflies) alone of 18,000 spotted off the South Coast of England.

A fun thing to know (who knows, it may help you win a pub quiz one day!) is that the Painted Lady is the only species of butterfly recorded from Iceland. I got this fact from the admirable UK Butterflies site, which contains numerous facts and photos about the lifestyle and food preferences of the Painted Lady that I'll not reiterate here. Suffice to say that caterpillars of the Painted Lady are dark and hairy and feed on thistles and nettles.

My searches for information on my butterfly were complicated by the fact that some sources seem to use the Latin name Vanessa cardui, others Cynthia cardui, and still others talk about the species cardui in the genus Vanessa and sub-genus Cynthia. I've not had a chance to sort out which is the professionally accepted name. Anyone?

Another topic my searches led me to was the (new for me) subject of 'foraging theory'. This is a huge topic and the reader should be take my (decidedly amateur) understanding and description with a 'health warning'. Briefly however my understanding goes like this: We've all watched bees and butterflies drifting through patches of flowers, or watched little songbirds working their way through the tree tops pecking at tidbits. Perhaps, like me, you've never really noticed any particular pattern or method to the foraging of these animal. At a glance, butterflies for example, seem to drift along haphazardly, landing on any such plant as they encounter and (one might presume) staying there for as long as it takes to drink a flower's nectar dry. In fact, many years of fabulously detailed studies by armies of biologists have shown that the foraging practices of many animals are anything but random. Quite the contrary, foraging animals have evolved highly specific methods and rhythms, carefully fine tuned to allow them to optimally gather food from their environments.

A classic example of decidedly non-random foraging was revealed by the studies by Messrs. Richardson and Verbeek (you can find one of their papers here) on the feeding habits of a population of crows in British Columbia. The crows were foraging on a beach for clams. Now, you might naively assume that a crow would simply gobble up any clam it came across. This fails to take account of the fact however, that a crow has first to open up a clam's shell in order to get at the meat inside. Now, little clams don't take much time and energy to open...but then, they don't yield much meat either. Huge clams yield lots meat...but they require the crow to spend a lot of time and energy to get them open. From this you start to realise that if a crow is to get the maximum food benefit from an hour (say) spent feeding, there will be some optimal clam size the crow should target in order to spend the least time for the most meat. Amazingly, this is what the studies showed: the crows were selecting just those sizes of clam that allowed them to maximise their average energy intake.

Similar studies have been replicated across many animals with the same results: crabs show optimised strategies similar to those of crows when selecting the size of mussels to open and eat; studies on brooding starlings show that parent starlings will continue to hunt for worms in the field until they are have just the number of worms held in their beaks that optimises the bird's efficiency in getting to and from the nest (Carry too few worms and the parents must make too many energy-sapping flights back and forth to feed the chicks. On the other hand, spending too long in the field trying to peck up worms with a beak already stuffed full is slow and cumbersome and results in the parent trying to carry an excessively heavy load back to the nest); Male Yellow dung flies show behaviour that optimises the balance of time and energy spent feeding vs. the time and energy spent in moving between dung heaps looking for females with which to mate.

Actually, although foraging behaviour can be discussed using words as above, in using phrases such as ' the maximum energy acquired per unit time' etc. the numerically minded amongst you may start to realise we are approaching the possibility of a mathematical desciption of foraging ( time-rates-of-change of quantities are the 'bread and butter' of the calculus you may recall from school). A mathematical description of foraging is just what the professional biological community has developed. The classic textbook Foraging Theory by Stephens and Krebs, gives a flavour.

Some of the seminal early work on foraging was by Charnov in 1970's. Charnov developed an important theorem known as the marginal value theorem which dealt with the situation of an animal foraging between patches of food spaced some distance apart (separated patches of flowers in a meadow for example). The question is, how long should a feeder spend in any given patch before moving on? Spend too long in one patch and the available food dwindles away (the animal is reduced to hunting around for the few remaining 'scraps' so to speak). Equally it takes time and energy to fly between patches. Charnov's theory was developed to predict the optimal time an animal should remain in any one patch in order to maximise its average rate of energy intake (or to put it another way, the foraging pattern resulting in the animal getting, on average, the most calories per hour).

All of which preamble, brings me back to the Painted Lady and the papers I came across by F.R. Hainsworth. Hainsworth studied whether Painted Ladies follow the predictions of the marginal value theorem. Specifically he studied how Painted Ladies reacted to being offered sugar-water solutions of varying strengths. Should Painted Ladies be following the predictions of the marginal value theorem then they should preferentially feed on those sugar solutions that would allow them to take up, on average, the most energy per hour. Now, a crow having to wrestle with opening a clam shell or a fly having to divide its precious time between feeding and mating is one thing. But you may wonder what's to stop a butterfly simply opting to feed on the most sugary solution offered every time? The answer is satisfyingly subtle: you must remember that a butterfly is constrained to having to feed through a straw! (The proboscis). If you imagine yourself being hungry but constrained to eat through a straw, you'll realise that whilst a thick gloopy syrup will certainly provide you more total energy than a thin watery one, sucking a jar of treacle through a straw is certainly no quick meal! When you realise this, an answer to the question of what sugar concentration in water will allow you to imbibe the most calories per hour is suddenly not so obvious.

I can't help but digress at this point to briefly address the question: How do you gather data on the feeding preferences of a butterfly? One option is to chase your specimen around a forest with a stopwatch! Preferable of course, is to find some way to get a captive butterfly to eat 'on demand' in the laboratory. This might sound tricky but Hawksworth provides a wonderfully simple solution that any suitably motivated amateur could replicate (naturally, you need a supply of butterflies but there are various companies on the web that will sell you eggs and caterpillars). The trick is to know that butterflies can taste through their feet! Gently hold your butterfly between thumb and finger, lower its feet into a dish of sugar water and, bingo!, it will instinctively unroll its proboscis and begin to feed. Get yourself a stopwatch and you're all ready to test the marginal value theorem!

Anyway to return to our main question: Are the eating habits of Painted Lady's in agreement with the marginal value theorem, with butterflies eating so as to maximise their average rate of energy uptake? Interestingly, the answer seems to be no. Instead, Painted Ladies go for meals that give them the most energy in one sitting (even though it may take longer to eat such a meal). This doesn't mean the marginal value theorem is 'wrong' (as above, it applies well in some situations), it simply means that one or more of the assumptions upon which this theorem is based don't apply to the Painted Lady. One suggestion is that rather than playing the 'long game' of choosing sugar solutions that maximise the calorie intake over a long period of time, newly emerged female butterflies are keen to pack in high calorie meals early, in order that they can quickly take on board enough energy to enable them to lay a large clutch of eggs. Whether this is the full story however appears to require more study...but then of course, you, dear reader, now know how to approach the task of conducting butterfly feeding experiments. I'm entirely confident therefore, that the answers will be with us shortly!

Helophilus pendulus hoverflies

I am an amateur naturalist trying to learn something about everything living in my garden.

Photo 1, taken back in September, shows two mating hoverflies resting on a leaf of my garden Buddleja bush. The characteristic brown stripes on the thorax quickly let me identify the species as Helophilus pendulus in my copy Hoverflies (Francis Gilbert, Richmond Publishing), an excellent monograph I've talked about before.

I assume the pair in photo 1 is male and female. Apparently it's normally possible to tell the two sexes apart in hoverflies by the eyes: The eyes of males touch at the top of the head, whereas those of females don't. Unfortunately this isn't true of Helophilus species. Why, generally, hoverfly sexes should differ in this regard, and specifically why they don't in Helophilus species, I can't imagine. Can anyone comment?

As I've mentioned previously, it's possible to distinguish hoverflies ('Syrphinae') from other flies by the veinature of the wings. In photo 2 I've zoomed in and enhanced the shot with my camera's software. Hoverfly wings have a 'false vein' (running approximately vertical in photo 2) and a section of vein at the edge of the wing that other flies lack.

In The Encyclopedia of Land Invertebrate Behaviour, the authors, R&K Preston-Mafham, describe male H. pendulus hoverflies as searching near flowers for females but often pouncing on other species of fly by mistake.

My copy of The Colour Guide to Hoverfly Larvae (G. Rotheray, Dipterists Digest 9) explains that the larvae of H. Pendulus thrive in farmyard drains and wet manure. Nice! My web searches also turned up a paper by one E. Stanley in the Veterinary Record 1845, 1(4) that describes finding an H. Pendulus maggot infesting the spinal marrow of a horse. By appearance they are a dark brown maggot with a tail as long as the body that acts as a breathing tube.

An obvious feature of hoverflies is the resemblance of many species to wasps and bees. Indeed, as explained in the extensive and very readable paper The Evolution of Imperfect Mimicry in Hoverflies by Francis Gilbert, at least a quarter of European hoverflies are mimics. Clearly, the mimicry is simply a matter of hoverflies trying to fool birds into thinking they are a wasp that will sting them....right? Well no actually, or at least it can be said the situation is far more subtle. As the paper above highlights the subject of animal mimicry is a complex one, much studied by biologists, and a topic where numerous questions and controversies persist.

Firstly, one should not assume that the 'warning colours' of hoverflies are, in all cases, a response to the threat of bird predation. There are plenty of other animals such as dragon flies, wasps and spiders will also eat hoverflies. Spiders have been shown to have an ability to recognise the threat posed by wasps in their web, and to treat them with greater caution than they do with other insects. At the same time, some experienced birds such as Flycatchers have been shown to be rather skilled at 'seeing through' the disguise of hoverflies - readily distinguishing them from wasps.

Next there is the issue of whether what we, with our human eyes, see as a resemblance to a wasp, is the same as what a predator perceives with eyes that might have very different characteristics to our own (different colour sensitivity etc.) Experiments studying the willingness of pigeons to peck at images of various hoverflies and wasps have shown that pigeons do broadly rank resemblances of hoverflies to wasps in the same way that we do. But there are exceptions with pigeons regarding Syrphus ribesii as the most wasp-like hoverfly of all, a view not shared by humans.

Next, there is the question of whether it is a bee's or wasp's sting that a predator is avoiding and that a hoverfly is "pretending" to posses. In fact, it seems that birds hardly ever suffer wasp stings and actually it is the unpleasant taste of a wasp's internal venom sack that some birds avoid. With Bumblebees (which some hoverflies mimic) the situation is more subtle still. There is some evidence that the sheer effort (in terms of wasted time and energy) involved in removing all the various hairs and largely inedible, chitinous, 'body armour' of a bumblebee is enough to put off some birds. Contrary to proclaiming its sting, the colouration of bumblebees (and their hoverfly mimics) may be a way of saying "I'm not worth the time and calories you'll get from eating me!".

This brings us to the difference between so-called Batesian mimicry and Mullerian mimicry. Batesian mimincry is the type of mimicry most of us imagine at first, whereby a harmless insect species evolves to copy the warning colours of a harmful one. By contrast, Mullerian mimicry involves two or more species that each have defences of their own, but nevertheless carry a common warning colour or form. Lots of bees and wasps all have yellow stripes for example. One can understand how this might arise: Suppose a predator has a bad experience with a harmful species. If that predator comes to associate the bad experience with a warning marking for that one species (yellow stripes say), then there's clearly potential benefit in other poisonous species adopting similar markings. By adopting similar markings however, one wasp species is not really 'copying' another, rather, both species are gaining benefit by evolving in parallel to advertise their venomous natures through similar body markings (multiple species settling on a 'common format' for advertising their individual danger signals if you will) . Now, in saying that hoverflies 'copy' wasps we are making the tacit assumption that hoverflies are harmless Batesian mimics. This is probably mostly the case. But it need not be universal. For example, it has been suggested that some species of hoverfly concentrate unpleasant tasting chemicals in their bodies through eating aphids that have been feeding on noxious plants. Such hoverflies would have their own defences (their noxious taste) and any evolved resemblance to say wasps, might then be an example of Mullerian mimicry.

The list of fascinating questions surrounding mimicry goes on. There is the question of the drawbacks of mimicry. Naively, it might seem there could little detriment for a species in 'wearing the clothes' of another. But suppose the venomous species being copied becomes rare. If a non-venomous hoverfly were to become more common than a venomous bee (say) it might be copying, what then? Predators would rarely (or even never) meet with the bad experience of finding that the prey in their mouth was the truly venomous one. After a time predators might simply stop associating the mimic's bright colours with danger. Indeed, the bright colours of the hoverfly mimic might become a positive liability, gaudily advertising the presence of a tasty snack! In summary, by choosing to copy the colours of another species, a mimic pays the price of shackling its population size that of the target insect being copied. Exactly the nature of the constraint (i.e. the mathematical relationship between the sustainable population of the mimic vs. the copied species) is a rich topic in its own right.

I could go on still further into a discussion of polymorphism in mimics, whereby a single species of say, hoverfly, comes in a number of different (colour) forms called morphs, and the benefits this confers. I've written enough for now however and so will leave this topic for another day, or, if you cannot wait for then, refer you to the paper above by Gilbert.

A lichen Aspicilia contorta

I am an amatuer naturalist trying to learn something about everything living in my garden.

Returning to the iron manhole cover I discussed in my last posting, photo 1 shows yet another lichen eking out a living on the metal surface. From my copy of Lichens (F. Dobson, Richmond Publishing) I'm fairly confident the lichen here is Aspicilia contorta.

The little 'volcanoes' I've marked in the picture are the lichen's spore producing fruits (apothecia). If you're trying to identify a species of a lichen it's worth knowing that apothecia come in different 'flavours', in particular lecideine and lecanorine apothecia. This is well covered in the text books, but I wasn't able to readily locate a picture on the web so I've drawn one myself (I'm no botanical illustrator as you can see!). The difference is in the margin of the fruit body: The margins of lecanorine lichen apothecia tend to be the same colour as the main underlying lichen body (thallus) and contain algae. By contrst, the margins of fruits of lecideine lichens tend to appear distinct from the thallus and do not contain algae. The latter are often black (the books sometimes refer to the margin being 'carbonised'. I don't know whether this is just poor terminology or whether the lichen really does manufacture something akin to raw carbon in the margin. Anyone?).

From the description above it will be clear Aspicilia contorta is a lecanorine lichen.

Actually, my efforts to track down a description of all this on web led me to encounter a fair amount of technical jargon surrounding apothecia that had me quite confused at first. To save any fellow interested amateurs out there the trouble of going through the same, drawing two and the description below summarises the understanding I managed to pick up.

As I'd understood from my previous experiments slicing up apothecia, lichen fuits comprise an array of asci (= little tubes filled with spores). Photo 2 shows a single ascus I managed to separate from an apothecium I took from my garden A. contorta. As shown in drawing 2, the asci come sandwiched amidts a mass of upright fungal threads ('hyphae') known as paraphyses. The specialist textbooks often include pictures of these paraphyses, as they too can help in identifying the species of a lichen.

The fact that the asci are neatly arranged in an upright position is of course, no accident. It's important to the reproductive success of the lichen that when spores exit an ascus, they do so into the open air. There would clearly be no point in having the asci oriented haphardly and liberting a substantial proportion of their spores into back into the walls of the apothecium from where they've arisen in the first place. Of course, this only explains why the asci stand upright, it doesn't explain how they know which way is 'up'. I was fascinated to learn recently however (from a copy of the classic Spore Discharge in Landplants (Ingold) that I was lucky enough to find in a secondhand bookshop) that many cup fungi are phototropic (= sensitive to the direction of daylight), and use this to beneficially orient themselves. The book describes this for various cup-fungi, and I assume it is also the mechanism used by lichens, though strictly, I haven't come across a reference to confirm this (anyone?).

The asci + paraphyses are arranged on a thin layer known as the hypothecium. This comprises a mass of dikaryotic fungal cells, each containing two DNA nuclei. By a complex process of chromosome divison (mitosis) these cells eventually form (single nucleus-) spores. The whole business of sexual reproduction in lichens is complex and there is probably a lot left to discover. The pdf document here has some details.

The outer part of the fruit (technically termed the excipulum) comprises a mass of single-DNA-nucleus (haploid) fungal cells.

So now you know!

Today's has been a rather technical posting and perhaps marks a suitable point to leave my garden's lichens for a while (though I have yet to exhaust them). Outside the first signs of Spring are here: The volume of birdsong is increasing as the breeding season approaches and today on a country walk I spotted my first ladybird of the year (despite Oxfordshire still suffering regular frosts at night), all of which suggests I will not have to look too hard for new signs of life in my garden. Until next time...