Science: Tick Time

As many a vacationer was finding out, the Argasidae and Ixodidae take their vacations in the winter. Last week, in woods and pastures almost all over the U.S., millions of them were ticking along like eight-day clocks. Wild animals, dogs, cattle and men were their unhappy hosts, and not infrequently their victims.

Argasidae and Ixodidae are the two U.S. tick families. In dozens of varieties they infect man with diseases that are often fatal: Kenya typhus, South African tick-bite fever, Bullis fever, Russian encephalitis, the Q fevers, tularemia (rabbit fever), tick paralysis, Rocky Mountain spotted fever. This summer, in southern Maryland, Texas, and other tick-infested areas, widespread experiments in spotted fever vaccination are being tried.

The tick, a remote cousin of the spider, is no true insect. Ticks and spiders have eight legs; bona fide insects have only six, the legal limit set by science. The tick’s extra pair of legs serves him well. When a tick senses an approaching meal, he hangs on to a low bush by his two hind legs and gropes hopefully with the other six. If, animal or man brushes past the bush, the tick grabs on with all eight legs, makes for the skin. Having attached himself, the tick bores in with his hard snout and begins to suck blood.

Female ticks are deadlier than males. They gorge themselves to the bursting point (five or six times normal size) and, if disease carriers, are just as dangerous to the tick picker who pops them as to the victim whose blood they suck. The male is flatter, smaller, less greedy. When he is sated, he noses around the host until he finds a feeding female, mates with her on the spot, moves away to start all over again. When the female is completely engorged, she drops off, finds herself a cranny to lay her eggs in (5,000 at a time), and begins the cycle once more.

Not all ticks carry fevers. Scientists estimate that only one in a hundred is infectious. But victims cannot tell which kind of tick has bitten them until they are on the way to the hospital.