The majority of sick monarch caterpillars have fly larvae eating them from the inside out. They're not actually sick with a bacteria or mould or other pathogens. In any case, I quickly decided it wasn't worth the risk of hurting my T with such an experiment. I got mealworms from a pet store instead. I'm giving my T a month to try to eat a mealworms on her own, otherwise I guess I have to deal with crushing worm heads.If you raise monarchs then im going to assume youll know if a caterpillar is sick and wont feed it. That would be my concern. But you must already know this.
as far as their poisonous status, thats something else. I have no idea how they could affect a tarantula. Asclepiades are toxic for humans to, aside from the parts that can be cooked and eaten. I guess youd only know by testing. I dont know if id try it.