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Latrodectus variolus

Common name: "Northern Black Widow"


Taxonomy: Originally described by Walckenaer, 1837

Kingdom: Animalia
Phylim: Arthropoda
Class: Arachnida
Order: Araneae
Suborder: Araneomorphae
Family: Therididae
Genus: Latrodectus
Species: variolus


Distribution:
 It is widely distributed from southern Canada, the eastern United States (east of Kansas, Oklahoma, and Texas) and south to northern Florida, it is more common in the northern part of its range. During the late spring mating season, it is common in Delaware,  New Jersey and Maryland. During late summer it is more common in Massachusetts, Connecticut and Michigan. It is found in southern Ontario, Canada in the late summer in small numbers.

Identification: L. variolus differs from the similar-looking species L. mactans by being a shiny black spider with skinny legs that has two distinct red marks for its "hour glass" pattern on the underside of its abdomen, and having three red spots along the upper side of the abdomen. L. mactans have the classic red hour glass pattern on the underside of its abdomen. The mature males are much smaller with abdominal markings that are more red-orange and either continuous or broken red-orange strip bordered by white down the dorsal midline of the abdomen. It also have several pairs of white stripes along the sides of the abdomen. Juvenile females can show a similar pattern of the mature males.

Web structure: Latrodectus species make an irregular web that is very strong with coarse silk usually near the ground in woodpiles, under stones, loose bark, in holes in the ground, around water faucets, around tree stumps, in garages, barns, outhouses and storage buildings. This species is not aggressive and will retreat in the presence of a human intruder. They only bite when bothered, pressed on, cornered or roughly handled (do not handle a widow spider!).

Egg sac: The sac is often guarded by the adult female L. variolus. It is pear-shaped, pale gray to yellow or tan, around 13-14 mm in length and 10-12 mm in diameter.

Egg sac production and offspring info: The average time from oviposition to emergence of the spiderlings (babies) is around 26 days. Spiderlings molt usually once, sometimes twice, before emerging from the egg sac. L. variolus females can produce up to six egg sacs from one mating. The first sac can contain up to 255 eggs and the last sac might have up to 30 eggs.

Size: Adult females are 9 to 11 mm and mature males are only 5.5 to 6 mm in length. L. variolus adult female are usually slightly larger than L. mactans females.

Longevity: Males take around 130 days to mature and can live post maturity for another 25 days. Females can live almost three years. Females mature around 7th or 8th instar.

Venom: Juveniles of both sexes and mature males can not bite to penetrate human skin. Sub-adult and adult females can. The venom attacks the nervous system. While the venom is powerful, the bite dispenses only a small amount of venom so fatalities are rare. Usually children under the age of seven, the elderly and/or anybody not in good health is more prone to have a bad symptons from the bite and even death resulting from the bite. Latrodectus species are not aggressive. Bites usually happen when the spider is pinched, pressed upon or started while guarding its egg sac.

Photo links:
Mature male L. variolus 
Adult female L. variolus

Adult female in web
Adult female with egg sac

References:

  • Howell, W.M. and R.L. Jenkins. 2004. Spiders of the Eastern United States: A Photographic Guide. Peason Eduction, Boston.

  • Kaston, B.J. 1978. How to Know the Spiders, 3rd edition. Wm. C. Brown Company, Dubuque, Iowa.

  • Vetter, R.S. and G.K. Isbister. 2008. Medical aspects of spider bites. Annual Review of Entomology 53: 409-29.
Commercial sale of Latrodectus species:

1) We will sell this species to adult, professional researchers in a minimum of 12 lots. See our Invertebrate researcher page by clicking HERE and our venomous species price list page by clicking HERE.

2) We will sell this species to private hobbyists ONLY if they fill out a venomous form which proves they are an adult and fully understand the responsibility and accountability of keeping venomous species. Inquire HERE for the venomous form to order. To order venomous species, go to our venomous species price list page by clicking HERE.