Reminder: After petting cats or dogs with oral (or topical) flea/tick medication, wash your hands well before touching caterpillars or their food. The medication is actually a pesticide that kills fleas and ticks. It gets into the dog’s body system, coming out in its skin oils and dander. When we pet them, we get it on our hands.
Some of the medications kill outright, causing caterpillars to vomit green and if it was strong enough, they die. Some of the medications cause improper pupation. Even others cause their mouth parts to work improperly, causing them to fail to eat well and they become weak and don’t grow normal.
Although chrysalises may be deformed due to other causes, flea/tick medication is one of the common causes for this problem.