Strange caterpillar behaviour

[Corrina]

Hello, my daughters collected a few cabbage white caterpillars the other day, some of which have now changed into pupae, but three have migrated to the top of the cage, "laid" some kind of small yellow eggs things, and are remaining close to these "eggs". The caterpillars are still alive, are not eating despite plentiful food in their cage, but are moving very little. Does anyone know what is happening here?

[Pete Eeles]

Yes - they have been parasitized by an ichneumon fly whose larvae have eaten the insides of the larva, and the small yellow eggs are actually cocoons of the fly - each will contain a fly pupa, and a fly will emerge in due course.

Unfortunately, the larva is doomed

Cheers,

- Pete

[Corrina]

Yuk! Well, thanks for that - I searched the internet high and low for an answer, but didn't suspect a parasite! At least we know what to do with them now... next step is to break it gently to the children.