Pholcidae

Cellar spiders
Pholcus phalangioides
Scientific classification
Kingdom:Animalia
Phylum:Arthropoda
Subphylum:Chelicerata
Class:Arachnida
Order:Araneae
Infraorder:Araneomorphae
Family:Pholcidae
C. L. Koch, 1851[1]
Genera

See text.

Diversity[2]
79 genera, 1461 species
Estimated range of Pholcidae.

Pholcidae, commonly known as cellar spiders, are a spider family in the suborder Araneomorphae. The family contains about 1500 species divided into about 80 genera.

Some species, especially Pholcus phalangioides, are commonly called daddy long-legs spider, granddaddy long-legs spider, carpenter spider, daddy long-legger, vibrating spider or skull spider.

Confusion often arises because the name "daddy long-legs" is also applied to two other, distantly related groups of arthropods: harvestmen (which are arachnids but not spiders) and crane flies (which are insects).

Appearance

Pholcids are thin and fragile arachnids. The body (resembling the shape of a peanut) being approximately 2–10 mm (0.08-0.39 inches) in length with legs which 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 caves, under rocks and loose bark, abandoned mammal burrows. In areas of human habitation pholcids construct webs in undisturbed areas in buildings such as attics and cellars (hence the common name "cellar spider").[3]

Behavior

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 before inflicting a fatal bite. The prey may be eaten immediately or stored for later. When finished they will "clean" the web by unhooking the prey and letting it drop from the web.

Threat response

Some species of Pholcidae exibit 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. While they are not the only species of spider to exhibit this behaviour, this behaviour 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 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.[4] If the spider continues to be harassed it will retreat into a corner or drop from its web and escape.

Diet

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 are natural predators of the Tegenaria species and are known to attack and eat redback spiders, huntsman spiders and house spiders.[5][6] Pholcids may be beneficial to humans living in regions with dense hobo spider populations as predation on Tegenaria may keep populations in check.[7]

Close-up of a cellar spider's head, showing two groups of three closely clustered eyes

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.

Systematics

Two Crossopriza lyoni. The bottom one is male. The female is clutching her egg bundle (magnified).
Smeringopus pallidus female with egg sac.
A cellar spider stays close to her young in Tulare, California.
A marbled cellar spider (Holocnemus pluchei) carrying prey.
Male shortbodied cellar spider (Spermophora senoculata) from the United States

As of November 2015, the World Spider Catalog accepts the following genera:[1]

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.[8] 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.[9]

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.[10] 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.[11]

Mythbusters experiment

During 2004, the Discovery Channel television show MythBusters tested the daddy long-legs venom myth in episode 13 - "Buried in concrete". Hosts Jamie Hyneman and Adam Savage first established that the spider's venom was not as toxic as other venoms, after being told about an experiment whereby mice were injected with venom from both a daddy long-legs and a black widow, with the black widow venom producing a much stronger reaction.

After measuring the spider's fangs at approximately 0.25 mm, Adam Savage inserted his hand into a container with several daddy-long-legs, and reported that he felt a bite which produced a mild, short-lived burning sensation. The bite did in fact penetrate his skin, but did not cause any notable harm.[12] Additionally, recent research has shown that pholcid venom is relatively weak in its effects on insects.[13]

References

Notes

  1. 1 2 "Family: Pholcidae C. L. Koch, 1850 (genus list)", World Spider Catalog, Natural History Museum Bern, retrieved 2015-11-10
  2. ↑ "Currently valid spider genera and species", World Spider Catalog, Natural History Museum Bern, retrieved 2015-11-10
  3. ↑ "Pholcidae information". BioKIDS – Kids' Inquiry of Diverse Species. Animal Diversity Web. Retrieved 15 July 2018.
  4. ↑ Marlin, Bruce (25 April 2006). Video of the "vibrating spider" vibrating (QuickTime Movie).
  5. ↑ "Daddy Long Legs". Queensland Museum.
  6. ↑ Wim van Egmond. "Pholcus phalangioides, the daddy-long-legs spider, in 3D".
  7. ↑ "Pholcus phalangioides (Long-bodied Cellar Spider) - Spider Identification & Pictures". spiderid.com. Retrieved 2018-07-15.
  8. ↑ "Daddy Long Legs Site on UCR".
  9. ↑ "Spider Myths – Daddy Long Legs".
  10. ↑ "Family Pholcidae – daddy long-leg spiders". Brisbane Insects and Spiders. 2009. Retrieved 13 November 2009.
  11. ↑ "Daddy long-legs".
  12. ↑ "Daddy long-leg spiders". Myth Files. Discovery channel.
  13. ↑ "The Spider Myths Site". Burke Museum. 12 May 2005.

Bibliography

  • Pinto-da-Rocha, R.; Machado, G.; Giribet, G., eds. (2007). Harvestmen – The biology of opiliones. Harvard University Press. ISBN 0-674-02343-9.
  • "North American Spiders, Family Pholcidae". Information and reference quality photos of cellar spiders. Includes QuickTime movie of spiders "vibrating".
  • "information and pictures of European Pholcidae".
  • "Tree of Life Pholcidae".
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