Mosquito bites frequently induce a sharp sting in people and some animals, with severe evolutionary consequences for the mosquito when it gets swatted. Are any mosquitoes evolving with delayed-action stings or reduced sting secretions so that they can drink blood without the threat of imminent death?
鈥� Mosquitoes have been around since the Jurassic period and probably evolved to feed on dinosaurs. Although we humans consider ourselves to be the most important animal on Earth, from the mosquito鈥檚 point of view we are somewhat irrelevant because they have evolved to feed on specific hosts. However, much like fleas, they will not pass up a meal if one is available from the wrong host.
I can make a useful comparison with my experience of the , Aedes albopictus. This Asian mosquito has recently invaded Europe and, to my chagrin, it took up residence in my locality last summer. Its bite is the most unpleasant I have ever experienced. It is simultaneously painful and itchy and causes a small bump to form, so presumably it鈥檚 not particularly adapted to humans. In fact, it will feed on any suitable host 鈥� bird or mammal.
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It attacks in swarms in full sunshine and can penetrate socks, jeans and T-shirts with ease. It is solenophagic, which means it thrusts its stylets directly into blood vessels and seems to take just a matter of seconds to be fully fed. You may swat some, but not all, especially if they are in the middle of your back, and often not before they have had time to feed.
Any survivor can lay a couple of hundred eggs and mate up to four times in its lifetime. The fact this mosquito is known to spread dengue and chikungunya means it must manage to feed on at least two victims, so it does not seem to be compromised by its painful bite.
Then again, those odd one or two mosquitoes that do find their way into my bedroom at night, when A. albopictus is not active, seem to be able to feed on me without leaving a trace. This morning I woke up with an itch behind my left knee. So some have already evolved to feed on me without me noticing, or at least without me noticing enough to try and swat them.
Terence Hollingworth, Blagnac, France
鈥� Your correspondent has confused bites and stings. A sting usually refers to a toxin injected into a host by a specialised organ, the organ itself or the resulting sensation, whereas a bite is performed by mouthparts.
Moreover, 鈥渂ite鈥� isn鈥檛 the best way to describe mosquitoes鈥� behaviour, as it implies the action of toothed jaws. Mosquitoes don鈥檛 sting; rather, they pierce their long mouthparts (proboscis) through the host鈥檚 skin. The proboscis comprises two tubes: one to suck up blood, the other to inject saliva. Only female mosquitoes bite, because they require protein from blood for egg production.
Nonetheless, female mosquitoes are likely to have undergone selection for an unnoticeable bite, as your correspondent supposes. As well as anticoagulants, mosquitoes do inject mild painkillers into the host via their saliva.
Sam Buckton, Chipperfield, Hertfordshire, UK
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