The Magnificent Puss Moth

Puss moth caterpillar

The puss moth caterpillar’s ‘eyes’ are only for display

A colleague working for Surrey Wildlife Trust kindly guided me to the location of this wonderful puss moth caterpillar (Cerura vinula) yesterday. A pair of them were contentedly grazing on aspen leaves.

Puss moth caterpillar grazing on aspen

Puss moth larvae feed on poplar, willow, or here on aspen

Colourful character

In adult form the furry grey and white moth flies at night between the months of May and July. The larval form looks much more exotic. The gawdy pink ring around its face gives the puss moth a very distinctive appearance.

Puss moth caterpillar

Head end of puss moth caterpillar

Self defence

If disturbed the puss moth caterpillar extends two whip-like appendages from its tail end and flails them around to deter attackers. It’s a bizarre and unexpected thing to witness.

Puss moth caterpillar tail

Puss moth caterpillar with extended ‘tails’

Puss moth caterpillar tail

‘Tail’ detail of puss moth larva

It also has the ability to squirt formic acid from its thorax if further provoked, but I didn’t try that!

Winter retreat

Shortly before pupation the caterpillar will change to a fetching shade of orange, and then again to purple.

It spins a cocoon of silk around itself and uses bits of tree bark as camouflage to stay hidden for the winter. The resulting cocoon is one of the strongest constructed by any UK moth.

I will have to return to see if I can find it in its various rainbow stages of development.

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Burnet Bodysnatchers

Caterpillars get a raw deal.

It’s true that the lucky winners in life morph into fabulous winged creatures which transcend their earthy origins, but a great many of their brethren seem destined to become nothing more than a convenient snack for any number of passing creatures.

Walking along the Purbeck coastal downland in mid summer I discovered a particularly unpleasant variation on this theme.

I was hoping to photograph some Adonis blue butterflies – a local speciality – but became mesmerised by a collection of tiny cocoons fastened to a grass stem. The more I looked, the more cocoons I found, but all appeared to have been vacated.

I couldn’t think what they might be, until additional exploration eventually uncovered their unfortunate victim nearby: a burnet moth caterpillar, seemingly tied to the stake:

Burnet caterpillar with cocoons

Burnet moth caterpillar parasitised by wasp larvae

This time the larvae were all too evident, as they appeared to be burrowing out of the caterpillar’s skin!

Further research reveals a fascinating tale of nature’s indifferent ingenuity:

The perpetrators in this instance are a species of Braconidae wasp which lay their eggs inside caterpillars.

When they hatch the larvae consume the caterpillar from the inside, but are careful to spare vital organs in order to keep their victim alive. Eventually the larvae cut their way out using specially adapted sharp mouthparts. When they emerge they immediately spin cocoons attached to the caterpillar.

Recent studies suggest that the larvae influence the caterpillar’s behaviour to remain in place and guard the cocoons. Thus brainwashed, the creature may even spin it’s own silk around the cocoons to further protect them. The wasps later hatch and the zombified caterpillar dies of hunger. Ain’t life great!

The Braconidae wasps don’t get it all their way however, as another variety of Ichneumon wasp parasitises the Braconidae pupae inside their own cocoons.

I found an example of this behaviour a bit further along the same stretch of coastal downland. The cocoons had been deserted by their caterpillar protector for some reason, which left them exposed.

Parasitic wasp

Ichneumon wasp parasitising Braconidae wasp pupae