The Hairy Caterpillar

When it comes to avoiding the unwelcome attention of potential predators, caterpillars must surely take the prize for the most diverse array of defensive ploys. Some are coloured so as to blend in with the vegetation upon which they are sitting; others are more obvious but pretend to be something else, like a dead stick or a bird dropping. Then there are those caterpillars which make a point of really standing out from the crowd, adopting bright, warning colouration to deter predators with the threat of a toxic or unpleasant meal.

Fortunately, the adoption of these different approaches often provides a basis for identifying the caterpillar you have just found lurking on some plant. Just the other day, for example, I was shown a small caterpillar on the leaf of our new pear tree at work. The dark, inch long larva was covered in an amazing array of coloured hairs, arranged in groups along the length of its body. At the head end there were two elongated tufts of dark hair, sticking out in front much like the tentacles of a garden snail. There were also shorter tufts along the back of the caterpillar; four yellow tufts towards the head end, all in a neat row, and smaller red ones towards the rear. In addition to these, the whole body was covered in fine long hairs of just the kind that would no doubt irritate the skin of a predator or over-inquisitive child. This combination of features revealed the caterpillar to be the larva of a vapourer moth. The adult vapourer is a fairly common species, on the wing from July through into October, and likely to be found in woodland and gardens across the county. Unusually, the female vapourer is wingless and presumably attracts the male to her through the use of pheromones. The eggs remain unhatched right through the winter and it is only the following spring that the distinctive caterpillars appear to feed on a range of tree species.

The evolution of such defensive ploys has been driven by natural selection, with moths from different families going down different evolutionary pathways, some which have led to the adoption of cryptic colouration, others to the development of chemical deterrents and colouration that advertises their presence. Of course it is not just the caterpillars which are under threat of predation; adult moths also show a range of approaches to reduce the chance that they will be eaten. This evolutionary arms race, between predator and prey, is repeated across species and groups worldwide. It is a race that is still ongoing and the strategies that we see today should not be regarded as an end point, merely a step in an ongoing evolutionary process.