Rearing Puss Moth Larvae

By Stephen Locke

 

On 27 May 2020, a female Puss Moth came to my moth trap and laid a dozen or so eggs – something which does happen from time to time – possibly a reaction to stress. 

An adult Puss Moth

The Puss Moth has the most spectacular larva, which a recent article in British Wildlife suggests is a snake mimic – a geologically ancient fear of snakes being genetically in-built in almost all animals. The eggs looked fertile, so I decided to rear them for the unusual and distinctive larvae. 

 Adult male Puss Moth, showing the fine antennae with which it locates females

The eggs laid in the trap on 27 May hatched nine days later on 4 June. Three other eggs came quite by accident with leaves of its food plant Goat Willow which I was collecting for the first batch. These came from willow planted by the developer as part of a wildlife hedge along the southern perimeter of a new housing development. This hedge has a good selection of native trees and shrubs and should provide a useful wildlife corridor. Anyway, a Puss Moth obviously found it to its liking.

The following photo shows a couple of larvae on 17 June. The little black one has just hatched and is about 5 mm long. The larger caterpillar is about 15 mm long – the green colouration develops after the first change of skin.

Larger 2-week old larva with a small black larva just hatched

Although when seen clearly, Puss Moth caterpillars are among the most flamboyant of all our caterpillars, their pattern can be very cryptic. Seen in their normal feeding position on the edge of a leaf, they can look just like a damaged and discoloured leaf.  A bird hunting quickly through the vegetation might well not notice it.

Well-camouflaged feeding larva

Equally, if they are disturbed, they adopt ‘scare tactics’ and the authors of the standard guide to British caterpillars believe they are snake-mimics: the caterpillar inflates its head to reveal large eyes and waves its tail filaments around like a snake’s forked tongue. The theory is that many animals have an instinctive and genetic fear of snakes (as opposed to learnt behaviour – they wouldn’t get a second chance!), so certain snake-like attributes are used by a number of animals to deter predators which show an instinctive avoidance of these features. 

The next two photos were taken on 24 June and the caterpillar is much larger – about 5 cm not counting the tail filaments.

 

Larva at nearly 3 weeks old

On 29 June, after 25 days of solid eating of Goat Willow, the two largest larvae successfully pupated. The two pictures below show a fully adult caterpillar in its final skin. 

 

Fully grown Puss Moth larva in final skin

Immediately before pupating, the caterpillar changes to a purple colour (without changing its skin) and wanders about looking for somewhere suitable to pupate. When fully extended, this caterpillar was 8 cm from head to end-of-tail filaments. 

Final stage before pupation

It then spins a cocoon within which it pupates. The pictures below show two cocoons made simultaneously by the two most mature caterpillars. I was surprised at how fast they did this – no more than an hour or so. These cocoons are not soft silk like a silk moth. Although made of silk, the caterpillar incorporates wood to make a cocoon which is really hard.

Hard cocoons incorporating wood made by Puss Moth larvae

As far as these individuals are concerned, that is it for the next 10 months. All being well, the adult moth will emerge in late April or May to start the whole cycle again. How such a delicate creature cuts open the cocoon is beyond me.

A third Puss Moth pupated on 1 July and a fourth shortly after. This completes the survivors of the trap-laid eggs. Two more larvae from the eggs I found by chance collecting food for the others seem to be doing well. But a lot can happen very quickly in a caterpillar's life, so fingers remain crossed.

  

   One of the two larvae reared from eggs found on Goat Willow,

one of their food plants (6 July)  

Postscript

The two remaining larvae from the eggs I found by chance both successfully pupated, the last on Wednesday 15 July. The pictures below show the last larva after its final colour change preparing to pupate, and the pupa incorporating wood it has chewed off the log. 

 Final larva preparing to pupate

Pupa incorporating chewed wood

So it has now entered a lockdown which will last for about 10 months, with hopes for successful emergences of all six moths in about late April or early May 2021.

The adult Puss Moth, like all its family, does not feed at all. The whole energy budget needed for metamorphosis, finding a mate and laying eggs next year to start the cycle again is now contained within the pupa, which must withstand the rigours of the next ten months carrying all hopes of a new generation.

The other day I found, without looking, a large Puss Moth caterpillar on the Goat Willow I use to feed the rest. I let it be, six being quite enough to look after, and it is encouraging to know that the hedgerow tree it was on was only planted a year or so ago. 

Update May 2021

On 20 May 2021, the first adult successfully emerged, exactly 292 days after it pupated – assuming that the first to pupate has been the first to hatch, though I don’t want to poke about with the unhatched pupae to check this. Assuming that is the case, the metamorphosis took nearly 11 months, but worthwhile to produce such a splendid insect, I think.

 

It could have chosen more clement weather to emerge, but I have tucked it away in a sheltered spot in the Goat Willow hedge and trust it will continue the cycle, and that the other pupae will also hatch okay.