A ticks sophisticated weaponry doesnt end with its needle-like mouthparts, capable of piercing through human skin and inflicting itchy agony. Each leg has a pair of claws that can grasp surfaces, and between them it has now been discovered is a foldable pad that can spread out like a fan and stick to the smoothest of surfaces. Ticks lie in wait on plants and leaf litter, until they can latch on to a passing warm-bodied bird or animal. They move about on their host and finally clamp down in a suitable place, plunging down their needle-like mouthparts. To do all this, a tick needs legs that can grip a large variety of surfaces, anchor the tick when a host is trying to scratch it out, and support the huge increase in body weight as it feeds a female tick can swell to 135 times her initial size after a blood meal. Tight grip Dagmar Voigt and Stanislav Gorb from the University of Kiel, Germany, have now used microscopy to look at the fine structure of the attachment devices on the legs of the castor bean tick (Ixodes ricinus) to tease out the different clinging mechanisms. A tick has four pairs of walking legs, each with elastic segments that give it great flexibility. At the end of each leg is a pair of curved circular claws. The tiny claws are well-suited to clasping tiny fibres, like miniature hair on plant and animal surfaces. Between the claws, the end of the tick leg has a foldable pad made of three lobes held together by tiny plates. The inside of the pad is a network of fibres embedded in a matrix, and the surface is covered with folds that can spread out like a fan. There have been multiple hypotheses about how ticks manage to cling on to different surfaces, says Voigt. The common opinion about tick attachment, so far, was interlocking with their claws. Our study finds proof of the adhesive properties of the pads on ticks feet. Elastic properties The surfaces of the pads, claws and the ends of the legs contain resilin, an elastic protein, the team found. A combination of the surface folds and the resilin makes the pads so elastic that the contact area with the host is enhanced. This increases the inter-molecular forces of attraction between the surfaces. The ticks also secrete a fluid through tiny pores on the pad surface, further increasing adhesion. The elastic claws can take loads by bending, and act like a spring in a clinging tick, much like a bendable beam, the authors say. If pulled away, the claw can snap back into place. We were rather surprised about the resilin in claws and the flexibility of claws, says Voigt. As far as we know, this is the first confirmation of resilin in arthropod claws. Female ticks attach with more force than males, and have more elaborate claws and pads, says Voigt. We suppose that these features enable the females to adhere properly for a longer period of time to hosts, to take up their blood meals, she says. Males dont take up much blood. Ticks dont permanently live on their hosts, though. Most of the time they live on the ground or on plants where smooth surfaces occur, says Werner Baumgartner of the Johannes Kepler University in Linz, Austria. He thinks ticks are likely to use sticky pads for the smooth surfaces, and claws for the rough ones.
New Scientist, 31 May 2017 ;http://www.newscientist.com/ ;