All the worms in my worm farm died with green stuff exploding from their bodies!?

I’ve recenelty had nearly all the worms die in two worm farms, and all the worms had a bulging green bit in the middle of their bodies which later explodes, splitting them in two. I have a few theories as to why this happened, such as pesticide on the vege scraps which poisoned them, or perhaps too much food added at once and the farm became anaerobic, or even too much cabbage added at once (there was a lot of cabbage)

Has anyone had this experience and/or know what caused this to happen? I appreciate any information you can provide.

Thanks!