Drinker moth caterpillar

This is the caterpillar of the drinker moth (Euthrix potatoria), photographed in the reserve on Sunday. It is so named because the caterpillar is believed to drink drops of dew on grass stems.

Drinker moth caterpillars like damp and marshy places best, riversides and fens, 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 header picture is of a caterpillar that hatched from the egg 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.

[1] Fully grown drinker moth caterpillar by DKG; [2] adult female drinker moth (CC0); [3] adult male moth

This caterpillar is probably fully-grown now, up to 7cm in length, and it will pupate soon. It will build a double walled papery cocoon on grass and reed stems, from which the adult moth will emerge in July. The adults are short lived: they mate and the females 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.

The caterpillars feed mainly at night, but despite this are particularly vulnerable to attack by parasitoid flies and wasps. During the day they can be found resting low down on vegetation.

Drinker moth populations have shown an encouraging recent recovery after a significant decline during the first part of the century.

Header image by Ian Bushell

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