A spider Meta segmentata

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

Photo 1, taken late last summer, shows a spider about half-a-centimetre long. Spiders are surprisingly tricky to identify. You might think their often striking colour patterns would make things easy. Unfortunately for many species this is rather variable and the only really accurate approach to identification is to examine your arachnid's reproductive parts under a hand lens. I didn't subject my spider to the indignity of this. From the illustrations in my copy of Spiders (M.Roberts, publ. Collins) however I'm tolerably confident the species here is either Meta segmentata or Meta mengei. Both are common in Britain and look very similar. From the season (M. segmentata is more common later in the year and M. mengei earlier) and from the book illustrations which show M. mengei with a more distinctly hairy lower-leg ('metatarsus I and II' - I've marked these with the white line in photo 1) than my spider appears to possess, I'm going with the identification M. segmentata.

The spider here is a male as revealed by the presence of the two little 'boxing gloves' (the 'palps') emerging just in front of the head. You can see these most clearly in photo 2.

In the course of writing this blog I have learnt to expect that any creature I come across will have some complex and fascinating aspect to its lifestyle. As I discovered from browsing various online papers (1, 2, 3 - references below) M. segmentata is no exception. The mating strategy of male segmenta's is one example of the rich topics for exploration:

If you're a male M.segmentata wanting to mate with a female it does not pay to approach her directly. Do this and its likely she'll eat you! Why it benefits some lifeforms to routinely indulge in cannibalism and others (we human males might say, thankfully) not is a puzzle in itself. Anyway, regardless of the reason, the best chance a male M.segmentata has of mating with a female is to approach her at just the moment she has caught a nice juicy fly and is sufficiently pre-occupied not to eat her suitor. In detail, what males actually do is to approach the female on her web, drive her off her catch and cut the threads supporting the dead fly so that it dangles from a single 'nuptial' thread. The male then mates with the female whilst she attempts to recover the catch.

For the male to be present at just the moment a female catches a fly requires that he sits, sometimes for weeks, watching her web. This is known as 'mate guarding' (in my previous posting I discussed mate guarding amongst dragonflies). Mate guarding for male M.segmentata's is a high energy-expenditure task. Not only may his own food supply suffer, but he is also exposed to challenges from other males who want to usurp his position of guarding a receptive female. (It seems that males know receptive females by the presence of pheromones on her web). The whole question of why it pays males in nature to expend considerable energy to mate is a very deep and rich one in biology (I said something about it in my posting here). An illustration of how subtle things can become is afforded by the studies of Rubenstein and others above (ref.1) on M. segmentata:

Careful studies of colonies of M. segmenta (e.g. on an isolated bushes) show that over a season, a 'size hierarchy' develops with the biggest healthiest males taking over guarding the biggest healthiest females. Once a big male has succeeded in mating with a female, he will move on and find another big female to start guarding. He may need to battle with an already on-guard male to win the right to guard this new female, but being large he stands a decent chance of winning any such battles. In this way big males get to mate with lots of big females and enjoy high reproductive success.

Little males have no hope of winning at this 'roaming' lifestyle however. They would constantly lose the battle to guard large females to larger males. So instead, small males adopt an alternative strategy and choose monogamy, 'settling down' with a single small female. Being small, she herself will normally have been pushed out to an 'undesirable' part of the colony (low down on the bush, say) where prey is scarce. Her small size and poor diet will mean she is not likely to be very fertile (she will not produce a lot of eggs). However, in settling down with her the little male avoids the alternative of a series of fruitless battles over larger females.

So far so good, but now, the question arises: What of mid-sized males? Should they roam, continually seeking large, fertile females to guard but mostly losing them in battles with large males? Or do as small males do and 'settle down' with a single female, but at the cost their mate may have low fertility. In the studies of Rubenstein, 86% of medium males opted to roam. Precisely why the odds stack in this direction doesn't seem to be understood; a nice example of how subtle behaviours can be in the natural kingdom and how there are plenty of topics awaiting further study.

References
1. Alternative reproductive tactics in the spider Meta segmentata, D.I.Rubenstein, Behav. Ecol. Sociobiol. (1987) 20:229-237
2. Mate guarding, competition and variation in size in male orb-web spiders, Metellina segmentata: a field experiment. J. Prenter, R. W. Elwood, W.I. Montgomery, Animal Behaviour, 2003, 66, 1053–1058
3. The influence of prey size and female reproductive state on the courtship of the autumn spider, Metallina segmentata: a field experiment, J. Prenter, R. Elwood, S. Colgan, Anim. Behav. 1994, 47, 449-456.

A macrochelidae mite

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

On a whim, I recently got out my trusty Baermann funnel (which sounds far more technical than it actually is, namely, a sieve for sieving tiny critters out of soil) and was pleased to discover a host of new-for-my-blog creatures in a handful of old grass clippings. One, a mite, is shown in Photo 1 (click on photo's to enlarge)

Readers of my blog will know I make some effort to research the species of any creature I find in my garden. In the case of my mite however, this turned out to be no small challenge. Before this posting I knew nothing about mites. As I discovered, there are at least three factors mitigating against the amateur seeking to identify one to species level.

Firstly, there is the obvious minute size of mites' physical features. Identification to species can depend on close examination of some minute gland on the body or joint in the jaw-parts ('chelicerae'). With only one specimen and the type of microscope equipment typically available to the amateur, such features can be a challenge to view. The professional may perhaps turn to an extensive university collection of carefully dissected and permanently mounted specimens or examine their find by electron microscope. Sadly however, I don't have a electron microscope in my garden shed (I'm open to donations!).

A second challenge is the sheer number of mite species. More than 45,000 (here) have been recorded and some sources estimate this may be only 5% of the number awaiting discovery. To make matters worse there seems to be a dearth of elementary texts or online keys in the area. A number of advanced texts are available (at suitably advanced cost!) but there seems to be little along the lines of a field guide aimed at the amateur (I'd be pleased to be corrected on this matter).

Attempting to work through academic journal papers and keys brings one to a third difficulty, namely the dense jargon that accompanies the study of mites (acarology). The amateur must wrestle with references to such arcane structures as pretarsal condylophores, filiform corniculae and Claperede's organs. To complicate matters still further, acaralogists refer to the hairs (setae) that decorate mites' bodies in code ('h1', 'pg3' etc.) and not only does there seem to be no simple online explanation of how this code works (anyone?) but there is more than one system in use amongst the professionals.

Thankfully however, there are some notable exceptions to the comments above. On his excellent web site David Walter Evans has put together a Glossary of Acarine Terms, indispensable for making sense of the jargon of acarology. For discussion of some current research topics in acarology and some superb images see Macromite's blog. My searches turned up very few online keys but notable exceptions are the one on David Evans' site above and the interactive key here on the site of the North American Bee-Associated Mites project.

It was the latter that enabled me to make some progress with my mite. I spent some time inputting various features into the key with limited success, but then noticed my mite had 'brush like arthropodrial processes on the chelicerae' (in English: a fringe of hairs on its pincer-like mouthparts). You can see these in photo 2. In the key above this immediately narrows things down from my mite being in any of 36 possible families, to it being in the single family macrochelidae. (As always my identifications come with a health warning - I'm happy for them to be corrected)

Unfortunately that is as far as the key takes me and from the webpages of Dr G.W. Krantz I learn there are still well over a hundred individual species in the macrochelidae family. The book to consult would appear to be A Review of the Macrochelidae of the British Isles by Hyatt and Emberson, but this is out of print and seems generally unavailable.

In the course of my searches I pleased to discover that I am not the only UK amateur taking an interest in the fauna beneath our feet. Over at Alan Hadly's splendid site he too is busy studying macrochelidae mites (together with a host of other critters).

I must end this posting here. My intention in writing my blog is to learn something of the natural history of the creatures I encounter. It may not have escaped the attention of the observant reader however, that in this article I have largely failed to say anything about the natural history of mites. I feel relaxed! With 44,999+ species potentially still at large in my garden, I suspect this will not be the last time I have an opportunity to study these tiny creatures...

Orb web Spider Tetragnatha extensa

I am an amateur U.K. naturalist trying to discover all the things living in my garden.

Further to the wealth of excitement my first spider posting provoked amongst my legions of readers (hem,hem), photo 1 (click to enlarge) shows another spider I found hanging in the centre of his web in an overgrown corner of my back garden (at (0,2) - see here).

You'll note I refer to my spider as a 'he': Using a hand lens I was able to confirm the presence of palps ending in swollen bulbs.

Back in late-April, when the photo was taken, working with my copy of Spiders (Michael Roberts, Collins Field Guide) I felt I came to a reasonably confident identification of my spider as Tetragnatha extensa. Looking now at my modest-resolution photo, I don't claim to unreservedly stand by this (T. montata might be a alternative (?) for example), but in the absence of better evidence it'll have to stand.

Eight species of the Tetragnatha spider genus are found in Northern Europe. All spin orb webs. Shortly after completeing the web, they take a few seconds to bite a hole out at the centre, there to take up residence waiting for lunch to arrive.

Gnath in biology refers to the jaws, hence Tetra'gnatha "four jaws", a reference to the fieresome mouthparts of these spiders. Photo 2 is my (untrained amateur's) attempt to sketch what would very likely be your terminal sight were you unfortunate enough to find yourself a small fly trapped in an extensa's orb web! The long 'mouthparts' on which the fangs are hinged are known as chelicerae. The chelicerae are used in mating, with the male and female locking theirs together. Atop the chelicerae sits the spider's turret-shaped head with its eight eyes.

T. extensa is one of the commonest Tetragnatha species in Britain and apparently tends to favour a residence close to open water (a slight puzzle in this case since, aside from an open water-butt, that corner of my garden doesn't have any). My copy of The Biology of Spiders (Foelix Rainer, Oxford Uni. Press) refers to a Tetragnatha spider being able to walk on water at 15-20cm/sec (the book doesn't state the species, but from the description I take it to be extensa).

Finally, in case you're wondering about the curious black cylindrical object on the left of photo 1: This is a handy design I got from Dr. Robert's book above for an insect (/spider) viewer. Very simply it comprises two concentric cylinders (in this case the plastic lids from two antiperspirant sprays). The larger has a hole cut in the top. The idea is to pop the insect between the two, and cover the hole with cling-film ('plastic wrap' to those of you reading in the US). By sliding the smaller tube up like a plunger, the insect becomes trapped, immobile against the film and hence easy to examine with a hand lens. Provided you don't keep it there too long, the critter need suffer no ill effects and can be set free afterwards. Neat heh!

The leaf galling mite Aceria macrorhynchus

I am an amateur trying to identify all the species living in my garden.

Despite my previous posting on the sycamore having been 'live' for a full three hours, I have been amazed to receive not one comment from my legions of avid readers (hem,hem) pointing out the obvious evidence for the second life form in photo 2 of that posting. Photo 1 (left, click on it to enlarge) gives you a second close-up opportunity. Of course, on second viewing you will immediately kick yourselves for not having noted the orange leaf galls, obviously (!) evincing the presence of the microscopic mite, Aceria macrohynchus.

In truth, I myself didn't have a clue what the cause of my leaf's little orange pimples was, and I spent some time looking through literature on rusts and smuts (little fungal entities that also commonly attack leaves). Eventually however I came across the site written by the good people of Hainault Forest, and later, a site on the fauna of Cornwall in the U.K. and the RX Wildlife site, and from these arrived at the (presumed) identity of my mite. From the RX Wildlife site I also learn that my mite also goes under the pseudonyms Eriophyes macrorhycus and Aceria cephaloneus.

I have two rather basic questions about my mite that I have little hope of being able to answer myself on a reasonable timescale, and am therefore hoping someone out there may help with:

i) Have I got the identification correct (A. macrorhynchus), or are there perhaps other mite species that cause orange pimples on sycamore leaves?

ii) What purpose do the galls serve? Do they act as living quarters for my mite, or do they have another purpose?

Some 45,000 species of mite have apparently been named and it is believed that many more remain undiscovered. Given many are sub-millimetre I imagine it must be an enormous challenge, even for the experts, to know whether the mite you have under your lens represents a new discovery or simply one the 45,000 that people have seen before. I learnt recently that in the case of the related, but distinct, sub-class of arthropods, the spiders, the sure-fire route to identification is microscopic examination of the palps or epigyne. Are there similarly diagnostic features for mites or are other methods needed?

Finally, I would love to see a photo of my mite, but have entirely failed to find one on the 'web. I did however come across the excellent mite site of the US Dept. of Agriculture. I did not find a picture of A. macrorynchus, but did find not only a photo but amazingly also a video of the Canadian Thistle Rust Mite Aceria anthocoptes. Since I understand that the images from the US DA are in the public domain, I'm reproducing it here (unless someone can tell me I shouldn't?). Since the Thistle mite above and my sycamore mite are in the same genus (Aceria) I'd like to believe they're of similar appearance. I'd be delighted if someone can point me to a photo of macrorynchus however.

Spider Amaurobius similis

After a somewhat lengthy break (apologies dear readers) it is time to get back to the task of identifying all the life in my garden.

Spring has sprung and with it I have begun to realise the size of my self-appointed task: my garden is humming with insects, and plants are shooting up faster than I can catalogue them. I am currently stockpiling photographs in the hope of returning to them during the quieter winter months. Enough preamble, on to today's posting:

Under some old slates in the corner of my garden (at (1.8,1.5) - see here) I found the spider in the photo left (click on it to enlarge). Based on the beautiful colour plates in my Field Guide to Spiders (Michael J. Roberts, publ. Collins) my indentification for her is Amaurobius similis (the lace webbed spider). Amauorbius ferox is apparantly closely similar. I can't be certain, but I'm going with similis on the basis of my spider's relatively large (for the UK anyway) size: I measured her as 16mm from from front foot to back. A. similis is normally smaller it seems.

Why her? Because, as I learn from book above, male and female spiders can be distinguished by the shape of the palps - the short pair of stubby 'legs' that stick out forwards from the spider's 'head'. Only one palp can be seen in photo 1. Enlarging photo 2 both are clearly visible. The palps of male spiders end in swollen 'bulbs', whereas in females they simply taper to a point (as in photo 2) or sometimes end in a small claw.

The male palps are designed for 'scooping up' sperm off the web during mating, before depositing it in the female's epigyne, an opening on the her underside. Under magnification the male palps show up as fantastically complicated: an intricate arrangement of hooks, nodules and even in some species inflatable 'balloons', all structures evolved to maximise the fit to the female of the species' epigyne. It seems you can make some progress identifying spiders by their general size and markings, but it seems microscopic examinations of the palp/epigyne is the 'acid test' for spider i.d. Dr Roberts' book is full of meticulously detailed pen and ink line drawings of palps and epigynes. I made some effort with a handlens to examine my female's epigyne, but I wasn't confident to be able to separate similis/ferox, so we'll all have to live with the uncertainty (unless some expert out there can remove it based on the photos ?).

Two other points of interest are visible in photo 2. Firstly the spiders massive mouth parts: the chelicera. These are not themselves the fangs (which are only barely visible in photo 2 at the tips of the chelicera) rather they are crushing mouth parts designed for grinding and chewing as the spider squirts digestive juices onto the unfortunate prey. Secondly, the tiny circle of eyes - I can only convince myself of four in the photo though there should be eight - staring beadily up at the camera.

The common name for A. similis "the lace webbed spider" derives from the extrodinarily fine silk webs it can produce. According to my copy of the Biology of Spiders (Rainer F. Foelix, publ. Oxford Uni. Press - a fascinating read, more in future postings) this may be only one-hundred-millionth of a metre in diameter, so fine that it scatters light and appears blue. This silk is produced from a special array of tiny 'funnels' known as the cribellum situated at the spider's rear. The cribellum accompanies the more familiar silk-producing spinnerets and is not present in all spiders. Members of the genus Amaurobiidae (5 species in Britain and N. Europe) are distinguished by having a cribellum that is sparated into two parts. Spiders with a cribellum also have a tiny array of hairs known as the calamistrum, situated on the hind legs and arranged as a comb. The spider uses this for combing-out the fine silk as it emerges.

Finally, a word about the fate that may await my female. If she mates successfully she will spin a silk 'nest' into which she will lay her eggs and carefully protect them until they hatch. A likely first meal of the young spiderlings will be...their mother. Gruesome stuff!