Spined Micrathena

Araneidae—Orbweavers

(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, although hikers may be familiar with the strong silk dragline it produces that stretches across trails at about eye level. It is found in most states east of the Rocky Mountains.

Description

The spined micrathena is a distinctively shaped 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 the color of these spiders. While many are mostly white and may have orange or brown spots, typically most are black with white markings. Males look quite different from females. They are brown and 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.

References

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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.

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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.