page_title: Tick
section_title: Diet and feeding
hierarchical_section_title: Tick / Biology / Diet and feeding
caption_attribution_description: English: Tick, on a blade of grass, forelegs extended hopefully to grab some passer-by. Central Massachusetts 20140703.
context_page_description: Ticks are arachnids, typically 3 to 5 mm long, part of the superorder Parasitiformes. Along with mites, they constitute the subclass Acari. Ticks are external parasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks evolved by the Cretaceous period, the most common form of fossilisation being amber immersion. Ticks are widely distributed around the world, especially in warm, humid climates.
  Almost all ticks belong to one of two major families, the Ixodidae or hard ticks, and the Argasidae or soft ticks. Adults have ovoid or pear-shaped bodies, which become engorged with blood when they feed, and eight legs. In addition to having a hard shield on their dorsal surfaces, hard ticks have a beak-like structure at the front containing the mouthparts, whereas soft ticks have their mouthparts on the underside of their bodies. Both families locate a potential host by odour or from changes in the environment.
  Ticks have four stages to their lifecycle, namely egg, larva, nymph, and adult. Ixodid ticks have three hosts, taking at least a year to complete their lifecycle.
context_section_description: Ticks satisfy all of their nutritional requirements as ectoparasites, feeding on a diet of blood. They are obligate hematophages, needing blood to survive and move from one stage of life to another. Ticks can fast for long periods, but eventually die if unable to find a host. This behavior evolved approximately 120 million years ago through adaptation to blood-feeding. The behavior evolved independently in the separate tick families, with differing host-tick interactions driving the evolutionary change.
  Some ticks attach quickly, while others wander around looking for thinner skin, such as is found on the ears of mammals. Depending on the species and life stage, preparing to feed can take from ten minutes to two hours. On locating a suitable feeding spot, the tick grasps the host's skin and cuts into the surface. It extracts blood by cutting a hole in the host's epidermis, into which it inserts its hypostome and prevents the blood from clotting by excreting an anticoagulant or platelet aggregation inhibitor.
  Ticks find their hosts by detecting animals' breath and body odors, or by sensing body heat, moisture, and vibrations. They are incapable of flying or jumping, but many tick species, particularly Ixodidae, lie in wait in a position known as "questing". While questing, ticks cling to leaves and grasses by their third and fourth pairs of legs. They hold the first pair of legs outstretched, waiting to grasp and climb on to any passing host. Tick questing heights tend to be correlated with the size of the desired host; nymphs and small species tend to quest close to the ground, where they may encounter small mammalian or bird hosts; adults climb higher into the vegetation, where larger hosts may be encountered. Some species are hunters and lurk near places where hosts may rest. Upon receiving an olfactory or other stimulus, they crawl or run across the intervening surface.
  Other ticks, mainly the Argasidae, are nidicolous, finding hosts in their nests, burrows, or caves. They use the same stimuli as non-nidicolous species to identify hosts, with body heat and odors often being the main factors. Many of them feed primarily on birds, though some Ornithodoros species, for example, feed on mammals. Both groups feed rapidly, typically biting painfully and drinking their fill within minutes. None of the species sticks to the host in the way that hard ticks do. Unlike the Ixodidae that have no fixed dwelling place except on the host, they live in sand, in crevices near animal dens or nests, or in human dwellings, where they come out nightly to attack roosting birds or emerge when they detect carbon dioxide in the breath of their hosts.
  Ixodidae remain in place until they are completely engorged. Their weight may increase by 200 to 600 times compared to their prefeeding weight. To accommodate this expansion, cell division takes place to facilitate enlargement of the cuticle. In the Argasidae, the tick's cuticle stretches to accommodate the fluid ingested, but does not grow new cells, with the weight of the tick increasing five- to tenfold over the unfed state. The tick then drops off the host and typically remains in the nest or burrow until its host returns to provide its next meal.
  Tick saliva contains about 1,500 to 3,000 proteins, depending on the tick species. The proteins with anti-inflammatory properties, called evasins, help ticks to feed for eight to ten days without being perceived by the host animal. Researchers are studying these evasins with the goal of developing drugs to neutralise the chemokines that cause inflammation in myocarditis, heart attack, and stroke.
caption: A questing tick, fingers for scale
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