Grass Spiders

Agelenopsis species

Grass spiders are very common in Pennsylvania and can be recognized by the large, somewhat concave, mostly horizontal, sheet-like web with a funnel or tunnel located off to one side. The webs are found on grass, weeds, and ground covers such as ivy, pachysandra, or periwinkle, and in numerous exterior places such as fencerows, bushes, and brush piles. Homeowners frequently see these fast-moving spiders indoors in the autumn as the spiders seek protection from falling temperatures.

Description

Grass spiders can be identified by their distinctive webs, the dorsal markings on the carapace and abdomen, and the greatly elongated hind spinnerets. Females are from 10 to 20 millimeters and the males from 9 to 18 millimeters in length. The carapace is yellow-brown to brown with a pair of darker, longitudinal bands extending back from the lateral eyes, and another pair of very thin lines located one on each side of the carapace. The abdomen is generally darker than the carapace and has a lighter median band, sometimes with a scalloped edge. The legs are frequently annulated, darker at the distal ends of the segments.

Life History/Behavior

The female deposits a lens-shaped, white egg sac in the late summer to fall. The eggs hatch in the spring and, after a series of molts, become adults in late summer. Although it is common to find these spiders entering structures in the fall, the adults do not overwinter.

As previously mentioned, the webs are found in many locations and serve as both a platform on which the spider captures prey and as a retreat in which the spiders can remain hidden. The grass spider web is not sticky but relies upon a network of threads above the sheet to divert or impede insect flight, causing them to fall onto the sheet, where they are captured by the rapidly running grass spider.

Medical Importance

There is no evidence that grass spider bites are medically important.

Authored by: Steve Jacobs, Sr. Extension Associate
March 2002, Revised 2006

References

Baerg, W. J. 1936. The Black Widow. Ark. Agr. Expt. Sta. Bul. 325. 34 pp.

Baerg, W. J. 1959. The Black Widow and Five Other Venomous Spiders in the United States. Ark. Agr. Expt. Sta. Bul. 608. 43 pp.

Breene, R. G., et al. 2003. Common Names of Arachnids. 5th ed. The American Arachnological Society Committee on Common Names of Arachnids. 42 pp.

Gertsch, W. J., and F. Ennik. 1983. “The spider genus Loxosceles in North America, Central America, and the West Indies (Araneae, Loxoscelidae).” Bul Amer Mus. Nat. Hist. 175: 24–360.

Herms, W. B., and M. T. James. 1961. Medical Entomology. 5th ed. The MacMillan Company, New York. 616 pp.

Kaston, B. J. 1948. “Spiders of Connecticut.” Conn. State Geol. Nat. Hist. Survey. Bull. 70. 874 pp.

Kaston, B. J. 1972. How to Know the Spiders. 3rd. ed. Wm. C. Brown Company, Dubuque, Iowa. 272 pp.

Levi, H. W. 1959. “The Spider Genus Latrodectus (Araneae, Theridiidae). Trans. Amer. Microscopical Soc. Vol. LXXVIII (1): 7–43.

Long, D., R. Snetsinger, and K. F. Helm. 1995. “Localized Pruritic Rash Due to Recurrent Spider Bites.” J. Geriatr. Dermatol. 3(6): 186–190.

Vetter, R. S., and P. Kirk Visscher. 1998. “Bites and Stings of Medically Important Venomous Arthropods.” International. J. Derm. 37: 481–496.

Vetter, R. S. et al. 2006. “Verified Bites By Yellow Sac Spiders (Genus Cheiracanthium) in the United States and Australia: Where Is The Necrosis?” Amer. J. Trop. Med. Hyg., 74(6) 1,043–1,048.