I found this cocoon on a chicken run whilst moving it - the casing (approx 3cm long) caught on a branch and came away from the wood, but seems to be made of wood pieces (1mm or less) taken from the wood frame leaving a shallow depression in the wood. The brown pupa? inside was approx 2.5 cm long, 6-7mm dia, but fell down into the wood stack, so cannot be located. What is it please?
This is the coocon of the Puss Moth, Cerura vinula, or one oth the other 'kittens' (Lepidoptera: Notodontidae).
The caterpillars feed on the leaves of poplars and willows. When they pupate they wander away from the tree to find a good spot and gnaw away some wood to form a depression, incorporating the wood chips into their coccoons. This provides camouflage and makes the cocoon extremely tough. What I have not worked out is how the moth (having lost its gnawing mouthparts) manages to escape from such a tuff cocoon - anyone answer that one?