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Insects do not usually attack unless they are provoked. Most bites and stings are defensive. The insects sting to protect their hives or nests.

A sting or bite injects venom composed of proteins and other substances that may trigger an allergic reaction in the victim. The sting also causes redness and swelling at the site of the sting.

• Bees, wasps, hornets, yellow jackets, and fire ants are members of the Hymenoptera family. Bites or stings from these species may cause serious reactions in people who are allergic to them. Death from bee stings is 3-4 times more common than death from snake bites (for more information, see stings of bees and wasps). Bees, wasps, and fire ants differ in how they inflict injury.
  
  
  • When a bee stings, it loses the entire injection apparatus (stinger) and actually dies in the process. A wasp can inflict multiple stings because it does not lose its injection apparatus after it stings.
    
    
  • Fire ants inject their venom by using their mandibles (the biting parts of their jaw) and rotating their bodies. They may inject venom many times.
  
  
• In contrast, bites from mosquitoes typically do not cause significant illnesses, unless they convey "vectors," or microorganisms that actually live within these mosquitoes. For instance, malaria is caused by an organism that spends part of its life cycle in a particular species of mosquitoes. West Nile virus is another disease spread by a mosquito.
  
  
• Other types of insects, bites, and diseases
  
  
  • Lice can transmit epidemic relapsing fever, caused by spirochetes.
    
    
  • Leishmaniasis, caused by the protozoan Leishmania, is carried by a sand fly.
    
    
  • Sleeping sickness in humans and a group of cattle diseases that are widespread in Africa, and known as nagana, are caused by protozoan trypanosomes transmitted by the bites of tsetse flies.
    
    
  • In unsanitary conditions, the common housefly can play an incidental role in the spread of human intestinal infections (such as typhoid and bacillary and amebic dysentery) by contamination of human food.
    
    
  • Tularemia can be spread by deer fly bites, the bubonic plague by fleas, and the epidemic typhus rickettsia by lice.
    
    
  • Various mosquitoes spread viral diseases (such as equine encephalitis; dengue and yellow fever in humans and other animals).
    
    
  • Ticks can transmit Lyme disease and other illnesses through their bites or stings.
    
    
  • Other insects such as chiggers and mites typically cause self-limited localized itchiness and swelling.
    
    
  • Serious bites from spiders, which are not insects, can be from the black widow or brown recluse.

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