Drinker moth caterpillar

While they were tidying up the edge of the big pond last week, the Friends found a drinker moth caterpillar (Euthrix potatoria), so called because it is believed to drink drops of dew on grass stems.

Drinker moth caterpillars are happiest in damp and marshy places like our pond edge, but anywhere grassy will do; grasses, particularly cocks-foot and canary grass, are their main food plants.

This is a species that overwinters in its larval stage; the caterpillar found by the pond will have hatched in July or August of last year. It hibernated in October when part grown, about 25 cm in length, and woke up in April this year.

Its distinctive tufts of hair, fore and aft, will already have developed by the time it went into hibernation. The hairs are an irritant and protect it from predators; take care if you handle a drinker moth caterpillar. In fact there is anecdotal evidence that it will use the hairs, or the chemicals that make the hair an irritant, in the structure of its cocoons.

Larval [1] and adult phases [2&3 female and male] of Euthrix potatoria

This caterpillar feeds mainly at night, but despite this is particularly vulnerable to attack by parasitoid flies and wasps. During the day it can be found resting low down on vegetation.

It will become fully-grown, up to 7cm in length, by June. It will pupate, building a double walled papery cocoon on grass and reed stems, from which the adult will emerge in July. The adults are short lived; they lay their eggs during July and August, the eggs hatch after ten to twelve days and the new caterpillars set off to do it all over again.

Drinker moth populations have shown an encouraging recent recovery after a significant decline during the first part of the century. Its conservation status is listed as common.

Header Image: Drinker moth caterpillar by Dave Price (CC BY-NC-ND 2.0) flickr.com

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