Itchy mosquitoes on the Net

In August 2001, a conscientious columnistfrom a science magazine for children whohad been asked this question delved further.How do mosquitoes home in on bloodvessels? ‘They must do a certain amount ofexploratory drilling before they strike blood.Do those probing punctures count as “bites”?Do they itch? If not, how long does it take fora mosquito to create the kind of feeding bitethat leaves an itchy welt?’Andrew Spielman(Harvard School of Public Health, MA,USA), who had worked on the subject inthe 1980s, responded and even offeredreferences: a mosquito drives its bundle ofsix feeding stylets (fascicle) verticallythrough the skin to a depth of about 1 mm tothe region where venules and arterioles aremost dense. She then thrusts and partiallywithdraws the fascicle repeatedly to nick avessel and make it bleed. If she fails to doso after some 15–20 thrusts (the ‘exploratorydrilling’) – and after about that manyseconds – she moves elsewhere and triesagain. Each thrust is accompanied by aspurt of saliva, which contains variousenzymes that interfere with plateletaggregation and facilitate the formation ofthe haematoma. If the mosquito senses thepresence of blood when withdrawing herfascicle, she stays still and begins to suck.The itch results from a sensitivity reaction toantigens in the saliva that are injected intothe ground substance of the skin during thesearch process. A‘bite’consists of a seriesof those random searches. It itches if theimmune system of the victim is sensitiveto the saliva of that species of mosquito. Asingle thrust can induce itching, how quicklydepends upon the person and the species.