Entomology (Study of Bugs)/mosquito bites


Why do mosquito bites itch for days after they have gotten their fill of blood? It causes us to kill and avoid them by the thousands, which would seem to be at their Darwinian disadvantage. Why didn't they mutate over the eons into a species whose bite didn't itch? Then they could bite us by the dozens and we wouldn't even notice it.

Hello Jackvdv,

That is a good question! Thanks for asking.

First, why do mosquito bites itch? A mosquito doesnít actually bite, if you want to get technical. She inserts her proboscis into your skin to suck out blood, leaving some of her saliva behind. Her saliva acts as an anticoagulant so she can feed more efficiently, which is a pretty neat adaptation if you think about it from her perspective! Our body then has an immune response to the foreign saliva, causing the swelling and itching. Immune responses like this protect us by letting us know that a foreign substance (that may or may not be harmful to us) is present.

Now, why havenít mosquitoes adapted to cause a bite that doesnít itch?

For adaptation to occur, natural selection must take place. For natural selection to take place, there must be adults with varying traits that can reproduce. The ones with traits that help them survive to reproduce pass on their genes, while the ones who die or cannot reproduce for other reasons do not pass on their genes. This is how the traits that are advantageous for survival and reproduction get passed onto new generations. This is how adaptation occurs.

So think about this: when a mosquito bites you, it is long gone by the time you start to itch, so you donít have the opportunity to kill that mosquito. If many mosquitoes were killed just after they imposed a bite, then this might lead to an adaptation because only mosquitoes that you didnít notice and kill would survive to reproduce and pass on their set of traits. In other words, mosquitoes still get away with feeding on you whether you itch later or not.

Now think about this: If the bite hurt when it happened, then you might notice and be able to kill the mosquito that bit you. This is just the kind of environmental pressure that leads to adaptation. Mosquitoes that donít hurt you when they bite survive to reproduce. The same saliva that carries the anticoagulant also has anesthetics in it to help prevent you from feeling the bite! Yay an adaptation!

If you are suffering from itchy bites, I would recommend a few things. Because it is an immune response, you can treat the bite the same way you might treat a rash. Ice the bite and take an antihistamine (like benedryl). This should help. Also, if you put meat tenderizer on the bite, it can make it go away. However, because I am not a doctor, you should probably discuss this with your doctor before trying it. I am not aware of the side effects or risks of putting meat tenderizer on your skin.

I hope this answers your question! Please let me know if you have others!


Entomology (Study of Bugs)

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Jessica Mellinger


I can answer questions about invertebrates native to California, including insects commonly found in homes. If you have an identification request, please attach a photo to your question.


I was involved in collection and identification of invertebrates for the United States Geological Survey, Biological Resources Division for six years. Also, I provided these same services intermittently for the UC Davis John Muir Institute of the Environment for many years. I have been a member of AllExperts.com since 2009.

Department of the Interior: United States Geological Survey, Davis Field Station; University of California, Davis Aggie Alumni Association; UC Davis Center for Neuroscience; U.S. Department of Veteran's Affairs

I have two B.A.'s from the University of California, Davis and two Associate's degrees from Sacramento City College.

Awards and Honors
Special Thanks for Achieving Results award from the Department of the Interior

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