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Spined Micrathena

Micrathena gracilis female

Micrathena gracilis female

(Micrathena gracilis)

Micrathena gracilis is commonly encountered in wooded locations, including landscaped residential and suburban locales. This spider is frequently overlooked because of its small size. But hikers would recall the strong silk dragline that it stretches across trails at about the eye level. It is found in most states east of the Rocky Mountains.

Description
The spined micrathena is a somewhat bizarre orbweaver. The females are typically black with white markings and have five pairs of black cones/spines/ conical tubercles encircling the lateral margins of the abdomen. The underside of the abdomen is cone shaped. There is great variability among these spiders. Many are mostly white and may have orange or brown spots. The more typical pattern and coloration found in Pennsylvania are represented in the photo. Males look quite different from females. They have elongated and more flattened abdomens that are blunted at the posterior. Females are 7.5 to 10 millimeters in length, while males are 4.5 to 5 millimeters long.

Life History/Behavior
This species overwinters in the egg stage. Males and females mature in early summer, and females can be found until October. Webs are built along flyways and trails that have bushes and vegetation spanning about 6 feet apart.

Medical Importance
This spider is not known to bite people and is probably not medically important.

Authored by: Steve Jacobs, Sr. Extension Associate
February 2015

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.

Bradley, R. A. 2013. Common Spiders of North America. University of California Press. 271 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.

Howell, W. M., and R. L. Jenkins. 2004. Spiders of the Eastern United States: A Photographic Guide. Pearson Education. 363 pp.

Isbister, G. K., and M. R. Gray. 2003. “Effects of envenoming by combfooted spiders of the genera Steatoda and Achaearanea (Family Theridiidae: Araneae) in Australia.” J. Toxicol. Clin. Toxicol. 41: 809–819.

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. 78(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.

McKeown, N., R. S. Vetter, and R. G. Hendrickson. 2014. “Verified spider bites in Oregon (USA) with the intent to assess hobo spider venom toxicity.” Toxicon 84: 51–55.

Ubick, D., P. Paquin, P. E. Cushing, and V. Roth, eds. 2005. Spiders of North America: An Identification Manual. American Arachnological Society. 377 pp.

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.

Vetter, R. S., and G.K. Isbister. 2008. “Medical aspects of spider bites.” Annu. Rev. Entomol. 53: 409–429.

 

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