caterpillar active defenses?

[Marion-Poll Frederic]

What do caterpillar regurgitate when attacked by a small predator that bite
them?

We work on Ostrinia nubilalis larvae (European corn borer) and we observed
that when they are
handled with forceps, they often try to attack the forceps by opening their
mandibles and excreting a liquid that looks like a regurgitate.

Has this behaviour been already described? does anyone know the composition
of this liquid (saliva or gut content)?

thanks for any cue

fred