|Urban Knowledge Master|
Brown widow spider
Lactrodectus mactans (Fabricius), Southern black widow
Lactrodectus hesperus (Chamberlin and Ivie), Western black widow
Julian R. Yates III
Extension Urban Entomologist
College of Tropical Agriculture and Human Resources
University of Hawaii at Manoa
Insects, smaller spiders, sow bugs, centipedes, etc.
L. mactans: Eastern North America, eastern Mexico, and the West Indies; L. Hesperus: Oklahoma, Kansas, and middle Texas throughout the southwestern states; L. geometricus: world wide in the tropical zone.
The potency of the black widow venom is well documented. Since the mouthparts (chelicerae) of the male are very small they are reputed to never bite. All encounters with man and animals can be attributed to the female. The bite of the western black widow has been described to cause a initial pain comparable to the prick of a needle and leaves two red puncture marks caused by the two fangs. This is followed by sharp pain which may lessen or persist for a number of hours. The pain moves from the site of the wound and settles in the abdomen and legs. Other ensuing neurological symptoms include nausea, vomiting, faintness, dizziness, tremors, loss of muscle tone, shock, speech disturbances, and general motor paralysis of various kinds. Anyone that suspects being bitten by a widow spider should seek immediate medical attention. Antivenon (Lyovac) is available for treatment. Death due to widow venom is rare and in untreated patients symptoms rarely persist for more than two days. Recorded deaths in older people were most probably due to complications and/or secondary infections originating at the wound site.
The brown widow spider is the one encountered by most people. And because of the presence of the "hour glass" marking on the ventral side of the spider's abdomen, the brown widow is often mistaken for one of the two black widow spiders. All three species have a black cephalothorax (united head and thorax), dark colored abdomen and long slender legs. Close examination of the brown widow spider shows that the base coloration is more correctly described as a dark brown or mahogany. In addition, the top surface of the abdomen has a distinct pattern of markings. The characteristic that most clearly differentiates the brown widow spider from the two black widows is the surface texture of the egg case. The brown widow egg case is textured and rough in appearance, due to the tufts of silk that are incorporated during the formation of the case. The surface of the black widow egg case is smooth. These egg cases can easily be spoted within the web, most often within the tunnel section where the female spider lives.
The eggs sacs can be constructed by the females in one to three hours and are approximately 1 cm in diameter. Each female can produce 10 to 20 of these sacs during a lifetime, and each sac may contain 200 to 250 eggs. The eggs hatch within the sac in about two weeks.
The spiderlings undergo their first molt three to four days thence. In approximately 10 days they emerge from the sac through one to three holes that are about 1 mm in diameter. The spiderlings remain in the nest area for several weeks (135-240 days) where they undergo six to nine molts before reaching maturity. Female black widows can live 850 to 950 days when food is readily available.
The brown widow spider is the most abundant and is commonly found in urban areas. It may be found indoors; however, favorite outdoor hiding places include the crawl space beneath homes and amongst piles of stored lumber, hollow tile blocks, abandoned vehicles, storage sheds, and stored items on shelves. Within the home, the brown widow may be found beneath tables and desks, behind shutters, in the angles of doors and windows, in the folds of clothing, in shoes, and under objects in dark, little-disturbed areas. The black widow spiders are less common and are generally associated with arid areas (western black widow) and higher elevations (southern black widow). Both can be found in crawl spaces, under rocks, in tiny voids, and in utility ducts.
Second instar spiderlings remain near sac but soon after climb to a high point where they spin silk threads and float out on the breeze. This method of "ballooning" provides a general dispersal of these spiders. They are shy and will tend to avoid contact with humans. Females are not aggressive, make no effort to attack, and prefer to retreat and lie perfectly still. When confronted or provoked, however, they will bite and inject a neurotoxic venom.
Their webs are usually about 30 cm in diameter.
Mechanical removal or destruction of these pests is the most satisfactory method of control. These spiders are delicate and can be easily injured or killed with a broom or stick. A vacuum cleaner can also be used to remove adult spiders and their egg cases. If this method is chosen, the vacuum cleaner bag should be removed and secured in a plastic bag for disposal. This will prevent the spiders or spiderlings from crawling out of the cleaner. Storing things neatly and the disposal of rubbish will discourage the formation of webs and nests both inside and outside the home. Periodic inspection of crawl spaces will also help to reduce populations of this pest.
A parasite, Baeus lactrodecti Dozier (Hymenoptera:Scelionidae), was introduced into Hawaii in 1939. This parasite will attack the eggs of L. mactans.
Spider control can be achieved by eliminating or by treating harborage sites with spot applications of an approved insecticide.
Ebeling, W. 1978. Urban Entomology. Division of Agricultural Sciences, University of California, Berkeley.
Funasaki, G. Y., Lai, Po-Yung, et. al. 1988. A review of biological control introductions in Hawaii: 1890 to 1985. Proc. Hawaiian Ent. Soc. 28:105-160.
Gertsch, W. J. 1979. American Spiders. Second edition. Van Nostrand Reinhold Company Inc.
Pinter, L. 1981. Widow spiders in Hawaii. PACDIV NAVFACENGCOM. U.S. Navy. Honolulu. Unpublished report.
Smith, Eric H. and Richard C. Whitman. 1992. NPCA Field Guide to Structural Pests. NPCA.