The reason mosquito bites itch is because they are injecting saliva into your skin. Saliva contains mosquito antigens, foreign particles that your body has evolved to attack with an inflammatory immune response that causes itching. The compound histamine is a key signaling molecule used by your body to drive this reaction.
In order for the mosquito to avoid provoking this reaction, they would either have to avoid leaving compounds inside of your body, or mutate those compounds so that they do not provoke an immune response. The human immune system is an adversarial opponent designed with an ability to recognize foreign particles generally. If it was tractable for organisms to reliably evolve to avoid provoking this response, that would represent a fundamental vulnerability in the human immune system.
Mosquitoe saliva does in fact contain anti-inflammatory, antihemostatic, and immunomodulatory compounds. So they’re trying! But also this means that mosquitos are evolved to put saliva inside of you when they feed, which means they’re inevitably going to expose the foreign particles they produce to your immune system.
There’s also a facet of selection bias making mosquitos appear unsuccessful at making their bites less itchy. If a mosquito did evolve to not provoke (as much of) an immune response and therefore less itching, redness and swelling, you probably wouldn’t notice they’d bitten you. People often perceive that some are prone to getting bitten, others aren’t. It may be that some of this is that some people don’t have as serious an immune response to mosquito bites, so they think they get bitten less often.
I’m sure there are several PhDs worth of research questions to investigate here—I’m a biomedical engineer with a good basic understanding of the immune system, but I don’t study mosquitos.
The reason mosquito bites itch is because they are injecting saliva into your skin. Saliva contains mosquito antigens, foreign particles that your body has evolved to attack with an inflammatory immune response that causes itching. The compound histamine is a key signaling molecule used by your body to drive this reaction.
In order for the mosquito to avoid provoking this reaction, they would either have to avoid leaving compounds inside of your body, or mutate those compounds so that they do not provoke an immune response. The human immune system is an adversarial opponent designed with an ability to recognize foreign particles generally. If it was tractable for organisms to reliably evolve to avoid provoking this response, that would represent a fundamental vulnerability in the human immune system.
Mosquitoe saliva does in fact contain anti-inflammatory, antihemostatic, and immunomodulatory compounds. So they’re trying! But also this means that mosquitos are evolved to put saliva inside of you when they feed, which means they’re inevitably going to expose the foreign particles they produce to your immune system.
There’s also a facet of selection bias making mosquitos appear unsuccessful at making their bites less itchy. If a mosquito did evolve to not provoke (as much of) an immune response and therefore less itching, redness and swelling, you probably wouldn’t notice they’d bitten you. People often perceive that some are prone to getting bitten, others aren’t. It may be that some of this is that some people don’t have as serious an immune response to mosquito bites, so they think they get bitten less often.
I’m sure there are several PhDs worth of research questions to investigate here—I’m a biomedical engineer with a good basic understanding of the immune system, but I don’t study mosquitos.