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Hannah Wood: Assassin Spiders from Around the World

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California Academy of Sciences

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The Assassin: A Spider That Actively Hunts Other Spiders

04 min 32 sec

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01 hr 00 min 00 sec

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Encyclopædia Britannica Articles

arachnid: Any member of the class Arachnida, primarily carnivorous arthropods having a well-developed head, a hard external skeleton, and four pairs of walking legs. Spiders and scorpions have a segmented body, but daddy longlegs, ticks, and mites do not. Arachnids range in size from tiny mites (0.003 in. [0.08 mm] long) to the 8-in. (21-cm) black scorpion of Africa. As arachnids grow, they molt several times (see molting). Most are unable to digest food internally; instead, they inject their prey with digestive fluids and suck the liquefied remains. Arachnids are found worldwide in nearly every habitat. Most groups are free-living, but some mites and ticks are parasitic and can carry serious diseases of animals and humans. Venomous spiders and scorpions also may pose a danger to humans. However, most arachnids are harmless and prey on insect pests.; arachnid on britannica.com
spider: 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. See also black widow; tarantula; wolf spider.; spider on britannica.com

© 2010 Encyclopædia Britannica, Inc.

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