Many bites and stings are uncomfortable, annoying and sometimes painful. In fewer cases they can be dangerous.

“Anytime you get bit by something that wants your blood, you can possibly get injected with a virus that can make you sick,” Dr. Ned Walker, a professor at Michigan State University in the Department of Entomology and the Department of Microbiology and Molecular Genetics, says.

All cases have a standard reaction, he adds. There is inflammation, redness and maybe swelling. “It’s very hard to tell what bit you unless you see it happen,” Dr. Walker says. In general, bites will itch while stings will hurt.