The Pholcidae are a family of araneomorph spiders. The family contains over 1,800 pholcids (individual species of the family Pholcidae), including those commonly known as the marbled cellar spider (Holocnemus pluchei), daddy long-legs spider, granddaddy long-legs spider, carpenter spider, daddy long-legger, vibrating spider, gyrating spider, long daddy, and skull spider. The family, first described by Carl Ludwig Koch in 1850, is divided into 94 genera.
The common name “daddy long-legs” is used for several species, especially Pholcus phalangioides, but is also the common name for several other arthropod groups, including harvestmen and crane flies.
Pholcids are thin and delicate arachnids. The body (resembling the shape of a peanut) is approximately 2–10 mm (0.08–0.39 inch) in length, and the legs may be up to 50 mm (1.97 inches) long. Pholcus and Smeringopus have cylindrical abdomens and eyes arranged in two lateral groups of three and two smaller median contiguous eyes. Arrangements of 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 without median eyes. Pholcids are gray to brown, sometimes clear, with banding or chevron markings.
Habitat
Pholcids are found in every continent in the world except Antarctica. Pholcids hang inverted in their messy and irregular-shaped webs. These webs are constructed in dark and damp recesses such as in caves, under rocks and loose bark, and in abandoned mammal burrows. In areas of human habitation pholcids construct webs in undisturbed areas in buildings such as high corners, attics and cellars (hence the common name “cellar spider”).
Trapping
The web of pholcids has no adhesive properties and instead relies on its irregular structure to trap prey. When pholcid spiders detect prey within their webs the spiders quickly envelop prey with silk-like material before inflicting a fatal bite. The prey may be eaten immediately or stored for later. When finished feeding they will clean the web by unhooking the remains of the prey and letting the carcass drop from the web. They are passive against humans.
Threat response
Some species of Pholcidae exhibit a threat response when disturbed by a touch to the web or entangled large prey. The arachnid responds by vibrating rapidly in a gyrating motion in its web. It may oscillate in tune with the elasticity of the web causing an oscillation larger than the motion of the spider’s legs. While other species of spider exhibit this behaviour, such behavior by the Pholcidae species has led to these spiders sometimes being called “vibrating spiders”. There are several proposed reasons for this threat response. The movement may make it difficult for a predator to locate or strike the spider, or may be a signal to an assumed rival to leave. Vibrating may also increase the chances of capturing insects that have just brushed their web and are still hovering nearby, or further entangle prey that may have otherwise been able to free itself. If the spider continues to be disturbed it will retreat into a corner or drop from its web and escape.
Diet
Although they do eat insects, certain species of these spiders invade webs of other spiders to 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 closer. Pholcids prey on Tegenaria funnel weaver spiders, and are known to attack and eat redback spiders, huntsman spiders and house spiders. Pholcids may be beneficial to humans living in regions with dense hobo spider populations as predation on Tegenaria may keep populations in check. They have also been observed to feed on the spider Steatoda nobilis in countries like Ireland and England.
Gait
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 spiders’ movements.
Misconceptions
There is a legend that daddy long-legs spiders have the most potent venom of any spider but that their fangs are either too small or too weak to puncture human skin; the same legend is also repeated of the harvestman and crane fly, also known as “daddy long-legs” in some regions. Indeed, pholcid spiders do have a short fang structure (called uncate due to its “hooked” shape). Brown recluse spiders also have uncate fang structure, but are able to deliver medically significant bites.
Possible explanations include: pholcid venom is not toxic to humans; pholcid uncate are smaller than those of brown recluse; or there is a musculature difference between the two arachnids, with recluses, being hunting spiders, possessing stronger muscles for fang penetration.[9] According to Rick Vetter of the University of California at Riverside, the daddy long-legs spider has never harmed a human, and there is no evidence that they are dangerous to humans.
The legend may result from the fact that the daddy long-legs spider preys upon deadly venomous spiders, such as the redback, a member of the black widow genus Latrodectus. To the extent that such entomological information was known to the general public, it was perhaps thought that if the daddy long-legs spider could kill a spider capable of delivering fatal bites to humans, then it must be more venomous, and the uncate fangs were regarded as prohibiting it from killing people. In reality, it is able to cast lengths of silk onto its prey, incapacitating them from a safe distance.
Source: Wikipedia
