Agelenidae

The Agelenidae are a large family of spiders in the suborder Araneomorphae. Well-known examples include the common "grass spiders" of the genus Agelenopsis. Nearly all Agelenidae are harmless to humans, but the bite of the hobo spider (Eratigena agrestis) may be medically significant, and some evidence suggests it might cause necrotic lesions.[1] However, the matter remains subject to debate.[2] The most widely accepted common name for members of the family is funnel weaver.[3]

For other spiders sometimes called "funnel-web spiders", see Funnel-web spider.

Funnel weavers
Grass spider (Agelenopsis sp.), female
Hobo spider (E. agrestis)
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Infraorder: Araneomorphae
Family: Agelenidae
C. L. Koch, 1837
Diversity
82 genera, 1307 species

Description

The body length of the smallest Agelenidae are about 4 millimetres (0.16 in) long, excluding the legs, while the larger species grow to 20 millimetres (0.79 in) long. Some exceptionally large species, like Eratigena atrica, may reach 5 to 10 centimetres (2.0 to 3.9 in) in total leg span.

Agelenids have eight eyes in two horizontal rows of four. The cephalothorax narrows somewhat towards the front where the eyes are. The abdomen is more or less oval, usually patterned with two rows of lines and spots. Some species have longitudinal lines on the dorsal surface of the cephalothorax, whereas other species do not; for example, the hobo spider does not, which assists in informally distinguishing it from similar-looking species.[4]

Biology

Most of the Agelenidae are very fast runners, especially on their webs. With speeds clocked at 1.73 ft/s (0.53 m/s), the giant house spider held the Guinness Book of World Records title for top spider speed until 1987. A recent literature review found peer-reviewed accounts of several agelenid species achieving speeds in this range, though some other taxa have achieved higher speeds.[5][6]

Agelenids build a flat sheet of nonsticky web with a funnel-shaped retreat to one side or occasionally in the middle, depending on the situation and species. Accordingly, "funnel weaver" is the most widely accepted common name for members of the family, but they should not be confused with the so-called "funnel-web tarantulas" or "funnel-web spiders" of mygalomorph families.[3]

The typical hunting mode for most sheet-building Agelenidae is similar to that of most other families of spiders that build sheet webs in the open, typically on grass or in scrubland as opposed to under bark, rocks, and the like. They await the arrival of prey such as grasshoppers that fall onto the horizontal web. Although the web is not sticky, it is full of entangling filaments that the spider continually lays down when passing over. The filaments catch in the least projections on a prey insect's body or limbs. The web also is springy, and whether perching on the sheet or awaiting prey in its retreat, the spider reacts immediately to vibrations, whether from a courting male, the threatening struggles of dangerous invaders, or the weaker struggles of potential meals. They attack promising prey by rushing out at high speed and dealing a paralysing venomous bite. Once the prey has been disabled, the spider generally drags it back into the retreat and begins to feed. This method of attack is consistent with the high speeds at which Agelenidae run. Other sheet web hunters such as some Pisauridae also are very fast runners.

Like any fast-running spider, the Agelenidae possess good vision, and are generally photosensitive (i.e. react to changes in the light), so they can successfully retreat upon perceiving a larger threat's shadow approaching. Some are also sensitive to wind blows, and can retreat before the prey even spots them. Males are less successful ambushers than females, so prefer to roam around and wander to new areas, rather than stay in one single web the whole time. In September, males of outdoors species (such as Agelenopsis and Agelena) can seek refuge within houses, usually nesting on or underneath outer windowsills, or also around the porch door. These spiders often are neither pest controllers nor pests themselves; they are very selective in their prey, and do not consume large quantities; also, they are immune to intimidation and come back to their webs even after being disturbed, unless they are completely destroyed.

Parasocial species

The type genus, Agelena, includes some parasocial spiders that live in complex communal webs in Africa. The best known of these is probably A. consociata. Social behaviour in these spiders comprises communal web-building, cooperative prey capture, and communal rearing of young. However, no trophallaxis occurs, nor any true eusociality such as occurs in the social Hymenoptera (ants, bees, and wasps); for example, the spiders have no castes such as sterile workers or soldiers, and all females are reproductive.[7]

Medical significance

Only one species of agelenid has become prominent as a putative cause of a significant frequency of necrotic arachnidism; this is the hobo spider, Eratigena agrestis.[4] This perception arose when the species was accidentally introduced to the United States in the mid-20th century and propagated rapidly in several regions. It is a fairly large, rapidly moving spider, and accordingly alarms many people.[8]

Genera
Main article: List of Agelenidae species

As of April 2019, the World Spider Catalog accepts the following genera:[9]

Agelenidae
  • female E. atrica at the mouth of her retreat
  • Funnel web of an agelenid from Spain
  • A. labyrinthica, male (immature)
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See also

References
  1. Goddard, Jerome (3 December 2012). Physician's Guide to Arthropods of Medical Importance (6th ed.). CRC Press. p. 380. ISBN 978-1-4398-5085-5 – via Google Books.
  2. Gaver-Wainwright, Melissa M.; Zack, Richard S.; Foradori, Matthew J.; Lavine, Laura Corley (2011). "Misdiagnosis of Spider Bites: Bacterial Associates, Mechanical Pathogen Transfer, and Hemolytic Potential of Venom from the Hobo Spider, Eratigena agrestis (Araneae: Agelenidae)". Journal of Medical Entomology. 48 (2): 382–388. doi:10.1603/ME09224.
  3. Breene; et al. (2003). Common Names of Arachnids (PDF) (5th ed.). Archived from the original (PDF) on 2006-09-27. Retrieved 2006-09-27.
  4. Vetter, R. S., and A. L. Antonelli. 2002. How to identify (or misidentify) the hobo spider. Wash. St. Coop. Ext. Pest Leafl. Series No. 116
  5. Spagna, J. C.; Peattie, A. M. (2012). "Terrestrial locomotion in arachnids". Journal of insect physiology. 58 (5): 599–606. doi:10.1016/j.jinsphys.2012.01.019. PMID 22326455.
  6. Gorb, S.N.; Barth, F.G. (1994). "Locomotor behavior during prey-capture of a fishing spider, Dolomedes plantarius (Araneae: Araneidae): galloping and stopping". The Journal of Arachnology. 22: 89–93.
  7. Rainer Foelix (3 December 2010). Biology of Spiders. Oxford University Press, USA. pp. 320–. ISBN 978-0-19-981324-7.
  8. Vetter, Richard S.; Isbister, Geoffrey K. (December 2004). "Do Hobo Spider Bites Cause Dermonecrotic Injuries?". Annals of Emergency Medicine. 44 (6): 605–7. doi:10.1016/j.annemergmed.2004.03.016. PMID 15573036.
  9. "Family: Agelenidae C. L. Koch, 1837". World Spider Catalog. Natural History Museum Bern. Retrieved 2019-04-22.

Further reading
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