Description
A small fraction of an inch in length, a typical tick has a roughly teardrop-shaped, two-part body encased in a leathery, accordion-like, dark brown external skeleton. One part – the tip of the teardrop – serves as its head, with a primitive brain, simple eyes, and mouth. The other part – the main swell of the teardrop – functions as an expandable body, containing the internal organs.
Perhaps most distinctively, our typical tick has a fiendishly designed feeding system. With simple eyes and specially adapted sensors, it can detect light, shadow, shapes, movement, exhaled carbon dioxide, smells and heat—all signals it uses to find and climb aboard potential hosts, including mammals, birds, reptiles and amphibians. With its mouth, which comprises a pair of jointed “palps,” a pair of “chelicerae,” and a barbed feeding tube, it selects and sets its dining table, uninvited, on the skin of its unwilling host. It uses the palps to choose the precise spot where it will puncture the skin. It uses the chelicerae to shield its feeding tube. It uses the feeding tube to penetrate the skin, producing a small excavation where blood can pool. It may use, not only the barbs of the feeding tube, but a glue-like substance from its salivary glands to firmly secure its connection to the skin. It uses its saliva both as a local anesthesia and as an anticoagulant. It makes sure that its host, feeling neither pain nor irritation, remains blissfully unaware of its presence. It makes sure that the blood supply will not clot but will remain fluid for sucking. As it sucks in blood, engorging its expandable body and external skeleton, the tick, depending on its species, may increase its body weight by as much as several hundred times, according to scientist Larisa Vredevoe, University of California, Davis, writing for her school’s entomology Internet site.
Most dangerously, according to University of Arizona’s Internet site, How to Bug Proof Your Home, “When a tick feeds it takes up whole blood, extracts the water (about 70-75% volume) and injects the water back into the host. For this reason, they are efficient vectors [carriers] of a variety of disease-causing organisms such as bacteria, spirochetes, rickettsiae, protozoa, viruses, nematodes, and toxins. A single tick bite can transmit multiple pathogens as well as creating secondary infections and allergic reactions. Ticks therefore are the most common transmitters of vector-borne disease in the U. S.”
A tick may belong to either of two families—the “hard” ticks, which have projecting and very noticeable mouthparts, or the “soft” ticks, which have barely noticeable projecting mouthparts.
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The Hard Tick
A hard tick, said Vredevoe, seeks “hosts by an interesting behavior called ‘questing.’” Typically, a questing hard tick, unable to fly or jump, climbs up low-growing vegetation near an animal run, where it waits, sometimes for months, for a target of opportunity. When the moment arrives, it uses its clawed front legs to latch onto the ankles or legs of the passing potential host.
The tick selects its mark, pierces the skin and begins sucking blood. Typically, the adult female behaves like a glutton, remaining in place until she is engorged, which may take several days. She may increase her body weight several hundred times. She then abandons her feeding site to lay eggs and die. The adult male feeds less ravenously, for it has come to the host for the primary purpose, not of finding a meal, but rather, of finding a mate. Opportunistically, it sometimes feeds, not on the host, but on an engorged female.
When the female hard tick abandons her feeding site, she lays a batch of 10,000 or more eggs then dies, according to the Pest Products Internet site. (The male typically dies soon after mating.)
An offspring will pass through three life stages during its life cycle. First, a newly hatched hard tick, or larva, or “seed” tick, which, oddly, possesses only six legs, immediately begins to seek its blood fortune. With luck, it will attach itself to a small mammal or reptile. Second, after engorging, probably over no more than several hours, it molts, emerging as a nymph, now with the full complement of eight legs. It repeats the feeding cycle, taking longer to engorge itself. Third, it molts once more, now emerging as an eight-legged adult tick. The adults repeat the feeding cycle over the several day period, which culminates in reproduction and death.
Depending on its species, a hard tick may remain on the same host throughout the three stages of its life cycle; or it may remain on the same host for the first two stages of its life cycle and find a new host for the third stage; or it may find a new host for each of the three stages of its life cycle. In the first instance, it would be called a “one-host tick,” Vredevoe said. In the second, it would be called a “two-host tick,” and in the third, a “three-host” tick. Its life cycle lasts no longer than perhaps a year in our desert basins, but it may live for three years or more in our forested mountain ranges.
More on ticks, the soft tick and how to remove them page 2
