violin spider: see brown recluse spider.

trap-door spider, spider of the same family as the native American tarantula. Trap-door spiders dig burrows, which they line with silk and protect by constructing one or two circular, hinged trap doors. The spiders emerge through the snug-fitting camouflaged doors to search for prey. Usually the burrow entrance has a door, the outer surface of which is camouflaged to blend in with the surrounding terrain. If a second door is present, it is usually below the entrance door. Trap-door spiders are classified in the phylum Arthropoda, class Arachnida, order Araneae, family Ctenizidae.

spider-flower: see caper.

spider, organism, mostly terrestrial, of the class Arachnida, order Araneae, with four pairs of legs and a two-part body consisting of a cephalothorax, or prosoma, and an unsegmented abdomen, or opisthosoma. The cephalothorax is covered by a shield, or carapace, and bears eight simple eyes. On the underside of the head (the cephalic part of the cephalothorax) are two pairs of appendages, the anterior pair called chelicerae and the second pair pedipalps, with which the spider captures and paralyzes its prey, injecting into it venom produced in the poison glands. The spider then liquefies the tissues of the prey with a digestive fluid and sucks this broth into its stomach where it may be stored in a digestive gland. Breathing is by means of tracheae (air tubes) or book lungs, or both. Arachnid book lungs are similar to the gill books of horseshoe crabs but are internal and adapted to a terrestrial habitat. Three pairs of spinnerets toward the tip of the abdomen produce protein-containing fluids that harden as they are drawn out to form silk threads. Several kinds of silk glands and spinnerets produce different kinds of silk used variously for constructing cocoons or egg sacs, spinning webs, and binding prey; other light strands are spun out for ballooning, or floating, the spiders, especially young ones, long distances on air currents. Spider silk is used for the cross hairs in certain optical instruments. Spiders live chiefly on insects and other arthropods; some large spiders ensnare and kill small snakes, birds, and mammals. Many are cannibalistic; the female may eat the male when courtship and mating are completed. Young, growing spiders can regenerate missing legs and parts of legs. Several species of spiders have bites that are exceptionally painful, or even dangerous to humans. Species of black widow spiders, which are found in the warmer parts of the world including the United States and S Canada, have a virulent neurotoxic venom. The bite venom of the brown recluse spider of SE and S central United States decomposes tissue, resulting in slow healing and sometimes leaving a sunken scar as large as a quarter. Among the more interesting spiders are the tarantula; its relative the trap-door spider, which ambushes its prey from a silk-lined burrow covered by a hinged lid; the orb weavers, which spin beautiful circular webs; and the crab spider, jumping spider, and wolf spider, named for their habits. Spiders are classified in the phylum Arthropoda, class Arachnida, order Araneae.

sea spider, common name for members of the class Pycnogonida, long-legged, rather spiderlike organisms of the phylum Chelicerata, widely distributed in marine waters. Most are tiny, from 1 to 9 mm (0.04-0.36 in.), and live in littoral regions, crawling about over the surface of sessile animal colonies or seaweeds. Some live on or in clams. There are deep-sea forms, some becoming quite large; Colossendeis colossea has a leg span of nearly 2 ft (91 cm). Their unusual body form makes their relationships to other arthropods obscure. Nearly all of the body is composed of the anterior region (prosoma); a tiny tubular posterior region (opisthosoma) projects behind. A large proboscis is used to suck in food. At the base of the proboscis is a pair of modified appendages (chelicera) used to pick off bits of food and hold them in front of the mouth. The next appendages are a pair of leglike pedipalps, followed by a pair of specialized legs used by the male to carry eggs until they hatch. Four pairs of walking legs follow, but sometimes additional pairs are found. Members of this class are relatively common and widely distributed; well over 400 species are known. Sea spiders are classified in the phylum Chelicerata, class Pycnogonida.

red spider: see mite.

brown recluse spider or violin spider, poisonous nocturnal spider, Loxoceles reclusa, most common in the SE and S central United States. Adults are 3/8 in. (10 mm) long and are light brown with a dark, violin-shaped mark on the back near the head. In humans their venom kills the tissue surrounding a bite and leaves a deep sore, but only rarely does a bite result in death.

Name that originally referred to a species of southern European spider (Lycosa tarentula) but now refers to more than 175 spider species (family Lycosidae) found in North America, Europe, and north of the Arctic Circle. The body of L. tarentula, the largest species, is about 1 in. (2.5 cm) long. Most species have a long, broad, hairy brown body; stout, long legs; and strong, prominent jaws. Wolf spiders chase and pounce upon their prey, hunting mostly at night. Most species build a silk-lined, tubular nest in the ground, which they dig with their heavy front legs. A few species spin webs. The bite of L. tarentula produces no ill effects in humans.

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Venomous species (Loxosceles reclusa) of brown spider, most common in the western and southern U.S. The brown recluse is light-coloured, generally with a dark violin-shaped design on its back, for which it is sometimes called the violin spider. About 0.25 in. (7 mm) long, it has a leg span of about 1 in. (2.5 cm). It has extended its range into parts of the northern U.S. and is often found under stones or in dark corners inside buildings. The venom of the brown recluse destroys the walls of blood vessels near the site of the bite, sometimes causing a slow-healing skin ulcer. Bites are occasionally fatal.

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African plant of genus Chlorophytum (lily family). This popular houseplant has long, narrow, grassy green-and-white-striped leaves. Periodically a flower stem emerges, and tiny white flowers (not always produced) are replaced by young plantlets, which can then be detached and rooted.

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Any of four species (family Cebidae) of diurnal, arboreal New World monkeys found from Mexico to Brazil. Long-limbed and somewhat potbellied, they are 14–26 in. (35–66 cm) long and have thumbless hands and a heavily furred, prehensile 24–36-in. (60–92-cm) tail. The coat is gray, reddish, brown, or black. They swing through branches, using their tails and hands, or leap or drop spread-eagled from tree to tree. They eat fruit, nuts, flowers, and buds. They are used in laboratory studies of malaria, to which they are susceptible. Though sometimes kept as pets, adults are likely to throw tantrums and may be dangerous.

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or red spider

Any plant-feeding mite in the family Tetranychidae, common pests on houseplants and agriculturally important plants. Adult spider mites are tiny, about 0.02 in. (0.5 mm) long, and often red. They spin a loose silk webbing on infested plants. A heavy infestation can cause complete defoliation. Because of their increasing resistance to pesticides, they are difficult to control. One effective control is the use of another, predatory, mite species.

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Any species of sluggish marine crab in the widely distributed family Majidae (or Maiidae). Spider crabs have a beak-shaped head; thick, rounded body; and long, spindly legs. They use a mucuslike mouth secretion to fasten algae, sponges, and other organisms to the hairs, spines, and knobby projections covering the body. Most species are scavengers, especially of carrion. Their size varies greatly. The body of the European long-beaked spider crab (Macropodia rostrata) is less than 0.5 in. (1 cm) in diameter, whereas the Japanese giant crab (Macrocheira kaempferi), whose outstretched claws can measure 13 ft (4 m) from tip to tip, is perhaps the largest known arthropod.

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Any of approximately 38,000 predatory arachnid species, mostly terrestrial, in the order Araneida, abundant worldwide except in Antarctica. Spiders have two main body parts, eight legs, two pincerlike venomous appendages, and three pairs of spinnerets. Species range in length from 0.5 to about 90 mm (0.02 to 3.5 inches). The venom of a few species (e.g., brown recluse) is harmful to humans. Most species catch insect prey in a web of silk extruded from the spinnerets. Spiders change little during growth, except in size. Species are classified largely on the basis of the number and arrangement of eyes and the type of web. Seealso black widow; tarantula; wolf spider.

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Any of several black spiders in the genus Latrodectus with a venomous bite that is rarely fatal to humans. Black widow species are found worldwide, with three living in North America. In Australia it is called the redback. The females are shiny black, usually with a reddish hourglass-shaped design on the underside of the spherical abdomen and with a body about 1 in. (2.5 cm) long. The black widow preys on insects. The male, about one-fourth the female's size, is often killed and eaten by the female after mating (the source of its name).

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