Why haven’t mosquitos evolved to be less itchy? Is there just not enough selection pressure posed by humans yet? (yes probably) Or are they evolving towards that direction? (they of course already evolved towards being less itchy while biting, but not enough to make that lack-of-itch permanent)
this is a request for help i’ve been trying and failing to catch this one for god knows how long plz halp
tbh would be somewhat content coexisting with them (at the level of houseflies) as long as they evolved the itch and high-pitch noise away, modulo disease risk considerations.
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.
Because they have no reproductive advantage to being less itchy. You can kill them while they’re feeding, which is why they put lots of evolutionary effort into not being noticed. (They have an anesthetic in their saliva so you are unlikely to notice the bite.) By the time you develop the itchy bump, they’ve flown away and you can’t kill them.
There’s still some pressure, though. If the bites were permanently not itchy, then I may have not noticed that the mosquitos were in my room in the first place, and consequently would less likely pursue them directly. I guess that’s just not enough.
There’s also positive selection for itchiness. Mosquito spit contains dozens of carefully evolved proteins. We don’t know what they all are, but some of them are anticoagulants and anesthetics. Presumably they wouldn’t be there if they didn’t have a purpose. And your body, when it detects these foreign proteins, mounts a protective reaction, causing redness, swelling, and itching. IIRC, that reaction does a good job of killing any viruses that came in with the mosquito saliva. We’ve evolved to have that reaction. The itchiness is probably good for killing any bloodsuckers that don’t flee quickly. It certainly works against ticks.
Evolution is not our friend. It doesn’t give us what we want, just what we need.
I believe mosquitos do inject something to suppress your reaction to them, which is why you don’t notice bug bites until long after the bug is gone. There’s no reproductive advantage to the mosquito to extending that indefinitely.
I had something like locality in mind when writing this shortform, the context being: [I’m in my room → I notice itch → I realize there’s a mosquito somewhere in my room → I deliberately pursue and kill the mosquito that I wouldn’t have known existed without the itch]
But, again, this probably wouldn’t amount to much selection pressure, partially due to the fact that the vast majority of mosquito population exists in places where such locality doesn’t hold i.e. in an open environment.
But the evolutionary timescale at which mosquitos can adapt to avoid detection must be faster than that of humans adapting to find mosquitos itchy! Or so I thought—my current boring guess is that (1) mechanisms for the human body to detect foreign particles are fairly “broad”, (2) the required adaptation from the mosquitos to evade them are not-way-too-simple, and (3) we just haven’t put enough selection pressure to make such change happen.
Why haven’t mosquitos evolved to be less itchy? Is there just not enough selection pressure posed by humans yet? (yes probably) Or are they evolving towards that direction? (they of course already evolved towards being less itchy while biting, but not enough to make that lack-of-itch permanent)
this is a request for help i’ve been trying and failing to catch this one for god knows how long plz halptbh would be somewhat content coexisting with them (at the level of houseflies) as long as they evolved the itch and high-pitch noise away, modulo disease risk considerations.
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.
Because they have no reproductive advantage to being less itchy. You can kill them while they’re feeding, which is why they put lots of evolutionary effort into not being noticed. (They have an anesthetic in their saliva so you are unlikely to notice the bite.) By the time you develop the itchy bump, they’ve flown away and you can’t kill them.
There’s still some pressure, though. If the bites were permanently not itchy, then I may have not noticed that the mosquitos were in my room in the first place, and consequently would less likely pursue them directly. I guess that’s just not enough.
There’s also positive selection for itchiness. Mosquito spit contains dozens of carefully evolved proteins. We don’t know what they all are, but some of them are anticoagulants and anesthetics. Presumably they wouldn’t be there if they didn’t have a purpose. And your body, when it detects these foreign proteins, mounts a protective reaction, causing redness, swelling, and itching. IIRC, that reaction does a good job of killing any viruses that came in with the mosquito saliva. We’ve evolved to have that reaction. The itchiness is probably good for killing any bloodsuckers that don’t flee quickly. It certainly works against ticks.
Evolution is not our friend. It doesn’t give us what we want, just what we need.
I believe mosquitos do inject something to suppress your reaction to them, which is why you don’t notice bug bites until long after the bug is gone. There’s no reproductive advantage to the mosquito to extending that indefinitely.
Oh wow, that would make a ton of sense. Thanks Elizabeth!
I had something like locality in mind when writing this shortform, the context being: [I’m in my room → I notice itch → I realize there’s a mosquito somewhere in my room → I deliberately pursue and kill the mosquito that I wouldn’t have known existed without the itch]
But, again, this probably wouldn’t amount to much selection pressure, partially due to the fact that the vast majority of mosquito population exists in places where such locality doesn’t hold i.e. in an open environment.
In NZ we have biting bugs called sandflies which don’t do this—you can often tell the moment they get you.
The reason you find them itchy is because humans are selected to find them itchy most likely?
But the evolutionary timescale at which mosquitos can adapt to avoid detection must be faster than that of humans adapting to find mosquitos itchy! Or so I thought—my current boring guess is that (1) mechanisms for the human body to detect foreign particles are fairly “broad”, (2) the required adaptation from the mosquitos to evade them are not-way-too-simple, and (3) we just haven’t put enough selection pressure to make such change happen.
Yeah that would be my thinking as well.