The proboscis of the mosquito inserts painlessly because the jagged edge of the proboscis leaves only small points in contact.
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How Mosquitoes Use Six Needles to Suck Your Blood

“In mosquitoes the proboscis is a marvelously intricate structure…consisting of six different stylets, each adapted for a particular purpose–for making the primary incision, inserting anti-coagulant and digestive enzymes contained in the insect’s saliva and, finally, withdrawing the blood itself. All the stylets are secreted within a protective sheath formed by the labium or lower lip, which, during blood extraction, is slid up out of the way into a loop form.” (Wootton 1984:72)

“The mouthparts of female mosquitoes have evolved to form a special proboscis, a natural biomicroelectromechanical system (BMEMS), which is used for painlessly penetrating human skin and sucking blood. Scanning electron microscope observations show that the mosquito proboscis consists of a small bundle of long, tapering, and feeding stylets that are collectively called the fascicle, and a large scaly outer lower lip called the labium. During blood feeding, only the fascicle penetrates into the skin while the labium buckles back to remain on the surface of the skin…[The mosquito] uses the two maxillas as variable frequency microsaws with nanosharp teeth to advance into the skin tissue. This elegant BMEMS enables the mosquito to insert its feeding fascicle into human skin using an exceedingly small force (average of 16.5 μN).” (Kong and Wu 2010:1)

Last Updated September 14, 2016