Orb-weaver spider

Orb-weaver spiders or araneids are members of the spider family Araneidae. They are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields and forests. 'Orb' was previously used in English to mean 'circular', hence the English name of the group. Araneids have eight similar eyes, hairy or spiny legs, and no stridulating organs. The family is cosmopolitan, including many well-known large or brightly colored garden spiders. With 3122 species in 172 genera worldwide, Araneidae is the third-largest family of spiders (behind Salticidae and Linyphiidae). Araneid webs are constructed in a stereotyped fashion. A framework of nonsticky silk is built up before the spider adds a final spiral of silk covered in sticky droplets. Orb-webs are also produced by members of other spider families. The long-jawed orb weavers (Tetragnathidae) were formerly included in the Araneidae; they are closely related, being part of the superfamily Araneoidea. The family Arkyidae has been split off from the Araneidae. The cribellate or hackled orb-weavers (Uloboridae) belong to a different group of spiders. Their webs are strikingly similar, but use a different kind of sticky silk. Generally, orb-weaving spiders are three-clawed builders of flat webs with sticky spiral capture silk. The building of a web is an engineering feat, begun when the spider floats a line on the wind to another surface. The spider secures the line and then drops another line from the center, making a 'Y'. The rest of the scaffolding follows with many radii of nonsticky silk being constructed before a final spiral of sticky capture silk. The third claw is used to walk on the nonsticky part of the web. Characteristically, the prey insect that blunders into the sticky lines is stunned by a quick bite, and then wrapped in silk. If the prey is a venomous insect, such as a wasp, wrapping may precede biting and/or stinging. Many orb-weavers build a new web each day. Most orb-weavers tend to be active during the evening hours; they hide for most of the day. Generally, towards evening, the spider will consume the old web, rest for approximately an hour, then spin a new web in the same general location. Thus, the webs of orb-weavers are generally free of the accumulation of detritus common to other species, such as black widow spiders. Some orb-weavers do not build webs at all. Members of the genera Mastophora in the Americas, Cladomelea in Africa, and Ordgarius in Australia produce sticky globules, which contain a pheromone analog. The globule is hung from a silken thread dangled by the spider from its front legs. The pheromone analog attracts male moths of only a few species. These get stuck on the globule and are reeled in to be eaten. Both types of bolas spiders are highly camouflaged and difficult to locate. The spiny orb-weaving spiders in the genera Gasteracantha and Micrathena look like plant seeds or thorns hanging in their orb-webs. Some species of Gasteracantha have very long, horn-like spines protruding from their abdomens.