Puss Moth

Puss Moth
Cerura vinula

The adult Puss Moth

UK Native: Yes
Foodplants: Sallows and Willows (Salix spp.) or Aspens and Poplars (Populus spp.)

The Puss Moth is a species of moth that I have been intrigued with since I was a child, although I'd never had the chance to rear or breed them myself. This year, I decided that I would purchase some eggs and rear the caterpillars.

The adult moth is fluffy, predominantly white and heavily speckled with black or grey. Although this sounds dull, it is actually a rather handsome moth, and can be quite large. The fluffy legs and thorax give rise to the common name, as from certain angles, the moth can indeed resemble a cat.

An early final instar caterpillar, with the eye-spot markings now clearly visible.

However, for most people (and for me), the most interesting feature of this moth is the caterpillar. Firstly, the appearance changes radically, with each instar looking distinctly different from the last. The only similarity is the unusual 'tails' of this species, which are in fact modified claspers. However, the caterpillar is at it's most striking in it's final instar, being bright green, with a dark saddle on its upper side, outlined in white. The head is also surrounded by a reddish-orange 'face' complete with black eye spots. The caterpillars are known for their aggressive behaviour, and once they feel threatened, they will turn to face the direction of attack, waving their 'tails' about, whilst extending special red filaments called flagellae. If this initial warning is not heeded, the caterpillars may spray the attacker with formic acid, which can be at a concentration of up to 40%.

A caterpillar approaching maturity.

The cocoon is also an amazing feature of this species. When the caterpillar is fully grown, it usually wanders away from the foodplant, and its colour will change from bright green to a dull brown or purple. The cocoon is usually spun on the trunk of a tree, or other convenient place, and is extremely difficult to spot. The larva will chew up particles of wood and spin these into the cocoon, which then becomes rock hard. It is also perfectly camouflaged against the usual tree trunk background.

The finished cocoon on a bark shaving.

Rearing:
The caterpillars have proven very easy to rear, although once they have been introduced to a particular foodplant (i.e. Salix or Populus), they cannot be transferred to the other. The larvae also eat a considerable amount of food in the last instar, so a plentiful supply of either Willow or Poplar will be needed to rear them successfully.

Upon hatching, the caterpillars will eat part of their eggshells. They also have a tendency to gallop off around the container, even when there is a plentiful supply of willow or poplar leaves for them to feed on. They will, eventually, settle down and begin to feed, and small holes will soon appear in the leaves.

Puss Moth larvae immediately after hatching.

As the larvae grow, it is important that they are kept in a relatively large container, so that stems of the cut food plant can be placed inside the cage, allowing the caterpillars to adopt their typical resting position when they are not feeding. Ideally, stems should be placed in a container of moist compost as opposed to water. Willow leaves in particular do not stay fresh for longer than a day when cut, so access to fresh food will be needed daily.

The typical resting position of the Puss Moth larva.

As the caterpillars approach maturity, you will need to ensure that bits of tree bark or rotted wood are provided prior to pupation, so that the caterpillars may successfully spin their wooden reinforced cocoons. They will gallop around the cage for many hours in search of somewhere to pupate if they do not deem anywhere suitable!

A caterpillar that has just begun spinning its cocoon.

The cocoons will develop and hibernate through the winter, with the adult moths not emerging until the following spring. They should be kept in a suitable container, and kept in a sheltered position outside to overwinter. They can be brought in during the spring, and released after emergence.