Insect bites and stings occur when an insect is agitated and seeks to defend itself through its natural defense mechanisms, or when an insect seeks to feed off the bitten person. Insects inject formic acid, which can cause an immediate skin reaction often resulting in redness and swelling in the injured area. The sting from fire ants, bees, wasps and hornets are usually painful, and may stimulate dangerous allergic reaction called anaphylaxis for at-risk patients. Wasps can bite and sting at the same time. Bites from mosquitoes, fleas and mites are more likely to cause itching than pain
