Daddy Long Legs (Pholcidae)
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Pholcids are fragile arachnids, the body being 2–10 mm in length with legs which may be up to 50 mm long. Pholcus and Smeringopus have cylindrical abdomens and the eyes are arranged in two lateral groups of three and two smaller median contiguous eyes. Eight and six eyes both occur in this family. Spermophora has a small globose abdomen and its eyes are arranged in two groups of three and no median eyes. Pholcids are gray to brown with banding or chevron markings. The shape of the Pholcus and Smeringopus's body resembles that of a peanut.
Pholcids are found in every continent in the world besides Antarctica where it is too cold for them to survive. They hang inverted in messy, irregular, tangled webs. These webs are constructed in dark and damp recesses, in caves, under rocks and loose bark, abandoned mammal burrows in undisturbed areas in buildings and cellars, hence the common name "cellar spiders". However, Pholcids are also quite commonly found in warm, dry places, such as household windows and attics.
The web has no adhesive properties but the irregular structure traps insects, making escape difficult. The spider quickly envelops its prey with silk and then inflicts the fatal bite. The prey may be eaten immediately or stored for later.
When the spider is threatened by a touch to the web or when too large a prey becomes entangled, the spider vibrates rapidly in a gyrating motion in its web and becomes blurred and difficult to focus on. For this reason pholcids have sometimes been called "vibrating spiders", although they are not the only species to exhibit this behaviour. Doing so might make it difficult for a predator to see exactly where the spider is, may be intended to signal an assumed rival to leave, or may increase the chances of capturing insects that have just brushed their web and are still hovering nearby. If the spider continues to feel harassed it will retreat into a corner or drop from its web and escape.
Certain species of these seemingly benign spiders invade webs of other spiders and eat the host, the eggs or the prey. In some cases the spider vibrates the web of other spiders, mimicking the struggle of trapped prey to lure the host of the web closer. Pholcids are natural predators of the Tegenaria species, and are known to attack and eat redback spiders and huntsman spiders . It is this competition that helps keep Tegenaria populations in check, which may be advantageous to humans who live in regions with dense hobo spider populations.
Close-up of a cellar spider's head, showing two groups of three closely clustered eyes
Pholcus phalangioides often uses an alternating tetrapod gait (first right leg, then second left leg, then third right leg, etc.), which is commonly found in many spider species. However, frequent variations from this pattern have been documented during observations of the spide
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