tick, small, parasitic arachnid of the order Ixodida, closely related to the mites. Ticks, which are larger than the often microscopic mites, are all parasitic in at least one developmental stage; most parasitize mammals and birds although some have reptilian and amphibian hosts. The unsegmented body is typically oval and compact, and there are four pairs of legs. The movable head is attached to the body by a hinge. There are four stages in the tick life cycle: egg, larva, nymph, and adult, but soft ticks may go through several nymphal states. An anchoring structure in the tick's mouth enables it to embed its entire head under the skin of the host, where it sucks the host's blood. If a tick is pulled off the host, the head usually remains embedded in the skin. Members of the family (Argasidae) of soft ticks, with a membranous outer covering, hide in crevices and come out at night to suck blood; their bites are typically painful. Hard ticks (family Ixodidae), which have thickened outer plates made of chitin, remain attached to the host for long periods; their bites are typically painless.
Ticks transmit Rocky Mountain spotted fever, tularemia, Lyme disease, equine encephalitis, several forms of ehrlichiosis, and other diseases. Tick-borne diseases of livestock (e.g., babesiosis, anaplasmosis) are of great economic significance. Each species needs three different hosts to complete its life cycle. Typically the larval stage will feed on small reptiles, birds, or mammals; the nymph stage will parasitize larger vertebrates; and adults will parasitize large herbivores and livestock. The adult of the ixodid species Ixodes scapularis, the vector of Lyme disease and babesiosis in the E United States and Canada, usually chooses deer as its host (I. scapularis of all stages will feed on humans). The closely related I. pacificus, which transmits Lyme disease and Rocky Mountain spotted fever in the western states, prefers livestock in the adult stage. Ticks can sometimes harbor more than one disease organism at a time. Rapidly multiplying Asian long-horned ticks, Haemaphysalis longicornis, can also kill a young animal when the growing offspring consume a large quantity of its blood.
Ticks belong in the phylum Arthropoda, subphylum Chelicerata, class Arachnida, superorder Parasitiformes, order Ixodida (or Metastigmata).
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A pulse broadcast at 1-second intervals by standard frequency and time broadcasting stations to indicate the exact time.
A time interval equal to ¹⁄₆₀ second, used primarily in discussing computer operations.
Any arachnid comprising Ixodoidea; a bloodsucking parasite and important vector of various infectious diseases of humans and lower animals.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
Commerce the smallest increment of a price fluctuation in a commodity exchange. Tick size is usually 0.01% of the nominal value of the trading unit
1. any of various small parasitic arachnids of the families Ixodidae (hard ticks) and Argasidae, (soft ticks), typically living on the skin of warm-blooded animals and feeding on the blood and tissues of their hosts: order Acarina (mites and ticks)
2. any of certain other arachnids of the order Acarina
3. any of certain insects of the dipterous family Hippoboscidae that are ectoparasitic on horses, cattle, sheep, etc., esp the sheep ked
1. the strong covering of a pillow, mattress, etc.
Brit informal account or credit (esp in the phrase on tick)
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
1. A jiffy
(sense 1). 2. In simulations, the discrete unit
of time that passes between iterations of the simulation
mechanism. In AI applications, this amount of time is often
left unspecified, since the only constraint of interest is the
ordering of events. This sort of AI simulation is often
pejoratively referred to as "tick-tick-tick" simulation,
especially when the issue of simultaneity of events with long,
independent chains of causes is handwave
d. 3. In the FORTH
language, a single quote character.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)
tickOne clock cycle, or one "tick" of the clock. See clock cycle.
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