Thursday, August 20, 2009

Gatekeeper Pyronia tithonus

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

Photo 1, taken on a sunny day in recent July shows a butterfly I found resting on a post in my garden. A few minutes with a butterfly guide and there's no mistaking it as The Gatekeeper (Pyronia tithonus).

My Gatekeeper was very obliging and gave me oodles of time to fetch my camera and take photo's. I might have thought nothing of this, but then I came across a nice online study by Christopher Young of 516 butterflies visiting a UK garden over three seasons. P.tithonus 'stuck around' for the longest of all. Whether this is simple coincidence or whether it points to a behavioural trait of the Gatekeeper I've no idea (an unrecognised butterfly habit awaiting study?).

A second common name for the Gatekeeper is the Hedge Brown. For some reason I prefer the first, though I can't imagine how it originated (anyone?).

The Gatekeeper in photo 1 is a male as confirmed by the dusky patches towards the centre of the forewings. In preparing this posting I came across a number of websites declaring that these are a source of pheromones. I haven't managed to locate an authoritative account to confirm this however (anyone?).

The Gatekeeper is a member of the Nymphalidae family of butterflies that includes some 25 UK resident species, amongst them my previously blogged Peacock . An obvious feature of both are the 'eye' spots. My quotation marks are carefully chosen having come across an interesting article by Stevens As I learnt in researching my Peacock butterfly posting, many studies have shown that the conspicuous wing spots of certain butterflies have a valuable effect as anti-predator devices, acting to startle small birds about the seize the insect. It has been widely assumed that the reason for this is that, to the birds, the wingspots resemble the eyes of larger predators (hawks, owls etc.). The paper by Stevens casts doubt on this however since their ingenious test experiments imply that the most effective patterns are not necessarily those that most closely resemble the eyes of predators.

Caterpillars of the Gatekeeper eat grasses. You can find an image of one here.

Sadly, that is as much as I have managed to learn about the Gatekeeper. I should like to have read a 2001 paper by Conradt that my web searching tuned up. From the abstract, I understand the authors' studies to have shown that P.tithonus can detect and orient itself by landmarks up to 150m away (an impressive distance sensing range for a small insect I'm sure you'll agree). Sadly however, like so much internet information about the natural world, the details are viewable only by making a payment to a private publishing house. Not something I, as am amateur, am inclined to do. Alas therefore, my curiosity and yours, dear reader, must go unsatisfied!

Monday, August 17, 2009

Common Toad Bufo bufo

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

Weeding out my shrubbery recently, I was pleased and surprised to come across a second example of a UK amphibian to add to the first (a common frog) I wrote about last year: specifically a rather large toad. Sadly, by the time I had raced to my house and returned with my camera my toad had disappeared. My luck was in however as a few minutes spent hunting through the undergrowth turned up a second: the little fellow in photo 1.

Britain has only two species of toad. One, the Natterjack (Epidalea calamita), is a rare and protected species. I have never knowingly seen one myself. Our second is the Common Toad. There are various ways to tell the two apart but the most useful from the point of view of photo 1 is the paratoid gland which I've marked with a 'p' in photo 1 (click to enlarge). The fact that this is rather regular and pronounced indicates that mine is a Common Toad (Bufo bufo).

What I've learnt about the Common Toad has been mostly through reading The British Amphibians and Reptiles (Malcolm Smith, Collins New Naturalist). With regard to diet, the book contains the amusing quote (attributed to Newman 1869) "[the food of the toad] seems to consist of all living things that are susceptible to being swallowed". Bees, ants, whole snails, moths and young snakes have all been recorded in the diet of the Common. In the case of some larger South American and African toad species even full grown live mice are taken.

It seems possible the first, larger toad I saw and the second smaller one were a female and male respectively. Male Common toads average 60-65mm. Females are typically 10-15mm longer.

Common toads can live a surprisingly long time. Forty years has been recorded in captivity. They hibernate on land in burrows from around mid-October until mid-March when they emerge to spawn. Spawning continues until around the end of April. As is well known, toad spawn forms long 'necklaces' in the water as opposed to the more amorphous blobs formed by frogspawn.

Finally, a word about the predators of the Common Toad. Crows, magpies, rats and snakes are all known to eat toads (some of the former tending to eat the innards, leaving behind the unpleasant tasting skin). Prize for most gruesome predator has to go to the greenbottle fly Lucilia bufonivora however. Having located a victim an adult bufonivora lays up to 100 eggs on its unfortunate victim's back or thighs. Some time later the eggs hatch and the emergent maggots immediately make their way up the toad's back and into its eyes and from there into the nasal cavity. Within a few days the toad is dead. The maggots devour the corpse before dropping off to pupate in the soil and emerge a week or so later as adults ready to repeat the cycle. For those with a strong stomach you can see a photo of an infected toad here.