Was insecticide used on the grasshopper, and if so, what product? Permethrin is fairly safe in chickens, but others could be a problem. Read your label and post again. Some things are toxic, but it depends on how much is eaten. Just keep a close eye on the chickens. There are a couple of things that may be used to flush out poisons such as Epsom salts or molasses flushes, but use caution, since those can cause diarrhea and cause dehydration. Replace any lost fluids with water and electrolytes, such as SaveAChick.