Most reactions to insect bites or stings are mild. They can cause minor swelling, stinging, redness or itching. Sometimes, however, they can cause severe reactions such as a sting from a wasp, hornet, fire ant, or scorpion. Some insect bites or stings can cause diseases such as Bacterial Meningitis, West Nile Virus, Lyme Disease, or Rocky Mountain Spotted Fever.