Invertebrates
Tick
Ixodida · also called ticks
A tick is a mite that gave up everything else to drink blood. It has no meal but blood at any stage of its life, it waits — sometimes for over a year — on a grass stem for an animal to brush past, and once aboard it cuts in, cements its mouthparts down, and feeds for days while swelling to the size of a grape. Along the way it transmits more diseases to people and livestock than anything but the mosquito.
Overview
Ticks are the order Ixodida, blood-feeding arachnids — essentially large mites, kin to spiders and scorpions, with eight legs and a fused one-piece body. They live on every continent and in nearly every land habitat, most abundantly in humid forest, woodland edge, and rough grassland. Each tick takes just three big blood meals in its life: one as a larva, one as a nymph, one as an adult.
Questing
A tick cannot jump or fly. It climbs vegetation, grips with its back legs, and holds its front legs out, where a sensory organ detects breath, heat, vibration, and smell. It grabs any animal that touches the plant — a waiting posture called questing — then searches the skin for a sheltered spot before biting.
A painless bite
Tick saliva numbs the wound, stops blood clotting, suppresses the local immune response, and glues the mouthparts in place, so a feeding tick usually goes unnoticed for days. Those same saliva proteins are being studied as drugs.
Disease
Ticks transmit Lyme disease, spotted fevers, tick-borne encephalitis, babesiosis, and cattle fever, among others. Certain tick bites can also trigger alpha-gal syndrome, a lasting allergy to red meat. Prompt removal matters — most infections need many hours of attachment to transmit — so pull an attached tick straight out with fine tweezers gripped at the skin.
Status
Ticks are Not Evaluated and in no danger. Several medically important species are expanding their range as winters warm and deer increase, spreading Lyme disease and other illnesses into regions that had little before.
Tick: common questions
Is a tick an insect?
No. A tick is an arachnid, in the same class as spiders, scorpions, and mites, and specifically it is a large, blood-feeding mite. The clearest difference is leg count. An adult or nymph tick has eight legs, like all arachnids, while insects have six. Ticks also lack antennae and wings, and their head, thorax, and abdomen are fused into a single unsegmented body rather than the three distinct sections of an insect. Newly hatched tick larvae are an exception and have only six legs, gaining the last pair at the first moult, which sometimes causes them to be mistaken for insects.
How do ticks find and get onto a host?
Ticks do not jump, fly, or drop from trees. Most use a strategy called questing. The tick climbs to the tip of a grass blade, a leaf, or a twig at roughly the height of its preferred host, grips the vegetation with its rear legs, and stretches out its front legs, which carry a sensory pit called Haller's organ that picks up carbon dioxide from breath, body heat, moisture, vibration, and animal odours. When a host brushes against the vegetation the tick releases its grip and climbs aboard, then wanders over the skin looking for a thin, sheltered spot such as the hairline, an armpit, the groin, or behind an ear before biting.
What is the right way to remove an attached tick?
Use fine-tipped tweezers or a purpose-made tick tool, grip the tick as close to the skin as possible, right at the mouthparts, and pull straight out with steady, even pressure, without twisting or jerking. Do not apply heat, petroleum jelly, nail polish, or alcohol to try to make it back out, because a stressed tick may salivate more into the wound, which can raise the chance of infection. After removal, clean the bite and your hands, and note the date. Most tick-borne infections take many hours of attachment to transmit, so prompt removal matters. Watch the site for several weeks for an expanding rash, and see a doctor if a rash, fever, or aches appear.
Can a tick bite make you allergic to meat?
Yes, this is a real and increasingly recognised condition called alpha-gal syndrome. The bite of certain ticks, notably the lone star tick in North America but also tick species elsewhere, can sensitise a person to a sugar molecule called galactose-alpha-1,3-galactose, or alpha-gal, which is present in the meat and products of most mammals but not in people, poultry, or fish. After being sensitised, the person develops an allergic reaction, often hives, stomach upset, or in bad cases anaphylaxis, three to six hours after eating beef, pork, lamb, or other mammal products, including sometimes dairy and gelatin. The delay makes it hard to spot at first. The sensitivity can fade over years if further tick bites are avoided.