What is the survival advantage to insects of their bites making us itch?
Gillian Peall
Macclesfield, Cheshire, UK
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Biting insects are after our blood. To make it easier for them to imbibe it, their saliva contains an anticoagulant to stop clotting. The chemicals in their saliva enter our bloodstream, activating our immune system, which then sends a shedload of chemicals called histamines to the site in order to fight off the intruders. It is the histamines that cause the itching, hence the advice to use an anti-histamine cream.
As far as I know, and I am open to correction on this point, the brains of the insects are unable to associate a quick slurp of our blood with a delayed swipe from a human hand. They are either long gone from our skin, or their reactions are a lot quicker than ours. Those that are too slow are, of course, unable to pass on any genetic hints to their offspring.
Michael Price
Church Stretton, Shropshire, UK
I suggest that there is no advantage to the insect 鈥� the itch is a response that we have evolved to encourage us to avoid being bitten. This is because insects are vectors of many diseases, including malaria and yellow fever.
鈥淭he itch is a response that we have evolved to encourage us to avoid being bitten, asinsects are vectors of many diseases鈥�
The bites are the way that the infection is passed on to us, and the irritation is an evolutionary reaction to the anticoagulant that insects inject into us to make it easier for them to suck our blood. The evolved itch is to remind us not to let them do it. 鈥淥nce bitten, twice shy!鈥�
Peter Meehan
London, UK
Scratching an itch may distribute insects or eggs elsewhere, or to another host, and liberate blood for neighbouring insects.
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