Western Widow Spider Fact Sheet No. 5.605 Insect Series|Home and Garden by W.S. Cranshaw* The “widow” spiders are a group of brown or gray and banded. Male widows Quick Facts related spiders in the genus Latrodectus. may have the characteristic hourglass Several species occur in the United States, pattern, but coloration is often more orange • Widow spiders rarely, if ever, but the western widow, Latrodectus hesperus, and sometimes yellow. When mature, they bite when not within a web. is the overwhelmingly dominant species have large knob-like structures (pedipalps) Bites may be more likely if throughout Colorado. (The “true” black originating from the cephalothorax, or first the female is tending an egg widow, Latrodectus mactans, is more body segment. Aside from this last feature sac in the web, which she will common in eastern and southern areas of the (conspicuous pedipalps) they are similar in defend. country.) appearance to immature females. Widow spiders build sticky irregular • Widow spiders produce a mesh-type webs, typical of other spiders toxin that affects the nervous Identification in the cobweb spider family (Theridiidae). system. Muscle and chest Mature females of the western widow Widow spiders often live in ready-made pain or tightness are some of spider are generally round in form with a holes in dark, undisturbed sites. Therefore, the most common reactions bulbous abdomen. They usually reach a widow spiders are most often found in to the widow toxin. length of 1/4 to 1/3 inch. Adult females are abandoned rodent burrows, loose stone or distinctively shiny and dark colored, generally wood piles, or the corners of rooms, garages, • Widow spiders prefer to nest black or occasionally dark-brown. and outbuildings. They do not produce the near the ground, in dark, The distinguishing feature of all widows undisturbed areas. Outdoor (Latrodectus spp.) is the presence of a red nest sites include holes or red-orange “hourglass” pattern on the produced by small animals or underside of the abdomen. However, this around construction openings pattern can be highly variable with the and wood piles. western widow. The pattern may appear as two unconnected spots, as a roughly rectangular area, or be so faint as to be barely visible. The color of the “hourglass” may fade or intensify in color during the life of any individual widow spider. The immature stages of both sexes and adult male widow spiders may have red or red-orange or yellow spots and stripes on the top of their abdomen. Immature females can be colored gray or pale brown, with banding Figure 1: Western widow female in web. patterns. Darker coloration increases as they get older. The presence of an “hourglass” pattern on the underside of the abdomen occurs throughout their development. Males of the western widow are one- half to one-third the size of females, and they have a more elongate body form. (The body of the males typically range from 1/8 ©Colorado State University to 1/4-inch in length.) They are not usually Extension. 8/07. Revised 1/13. black in overall color, instead appearing light www.ext.colostate.edu

*W. Cranshaw, Colorado State University Extension entomology specialist and professor, bioagricultural sciences and pest management. 1/2013 Figure 2: Western widow male. symmetrical web typical of orb weaving small silk strands that allow them to catch spiders (Araneidae) or the distinctive dense wind currents and be carried in the air. and funnel patterned web of the common If young spiders find a suitable spot funnelweb spiders (Agelenidae). they begin to produce a web; however, the Spiders of Similar Appearance. majority die before successfully producing a Thecombination of the dark black web. Survivors feed on insects that become color, the irregular web shape, and the trapped in the web. They grow, molting distinctive spherical abdomen are useful several times, with females typically characteristics for separating widow spiders becoming mature in about 4 to 6 months. from other spider species. However, related, Males develop more rapidly because but harmless, combfooted/cob web spiders they go through fewer developmental produce similar webs and are often the stages (instars) and molt fewer times most common spiders found in homes. than the females. Developmental rates These harmless cobweb spiders are the are greatly influenced by temperature same general shape as widow spiders, but and the availability of food. In laboratory are smaller and are either mottled brown conditions, mature females can live over a Figure 3: Underside of female western widow. or are dark brown or black with a white year after becoming mature. Males typically band around the front of the abdomen. At live only a few weeks. Under optimum quick glance one can confuse these with conditions, widow spiders can live two immature black widows, but they invariably years or more. The normal life cycle is lack the underside hourglass pattern or one year. bright coloring of the immature and male Black widows survive winter as either widow spiders. mature or immature forms. During cold Cobweb spiders that are most easily weather, spider development outdoors confused with widows are in the genus ceases and the spiders seek refuge under Steatoda. These cob web spiders are stones or other cover. Black widows similarly black and have the same enlarged can develop year-round indoors and abdomen as widow spiders. However, many move into homes by autumn for they lack the orange-red hourglass on the winter protection. underside of the abdomen, have prominent white markings on the top of the abdomen, and often have a white band around the Mating anterior edge of the abdomen. Although females of many spider species, including widow spiders, occasionally feed on males if the female Life History and Habits is hungry, this cannibalistic behavior Eggs of widow spiders are laid in an is not the norm despite the common Figure 4: Male and female widow spider. egg sac, attached to the web of the mother. misconception. Egg sacs produced by the western widow Male spiders wander and seek females are pear shaped and light whitish yellow for mating. When a female is encountered, to brown. About 200 eggs may be laid the male cautiously approaches the female, per egg sac. Under favorable conditions, periodically vibrating the web in a species- females may produce several egg sacs in specific manner. If the female is receptive, their lifetime. she will respond to the male’s signals by Eggs hatch in the egg sac about 2 weeks sending her own vibrational signals. The after they are laid. The newly hatched male then approaches the female and may spiders, known as “spiderlings,” remain in engage in contact courtship behavior. In the sac for several days and molt inside the successful matings, the male may finally egg sac. After this first molt, they leave the reach the female in about 30 minutes. sac by cutting an opening with their fangs. However, aggressive females, those that Spiderlings may remain clustered near the are particularly hungry, may charge the female in or near her web until the yolk approaching male and cause him to delay leftover from the egg stage is completely or abandon his attempt. digested. At that time, they disperse and Once touching the female, courtship Figure 5: Male widow mating with female. leave the egg sac, often by a process called begins as a tapping of the legs. The male “ballooning.” Ballooning spiderlings release then inseminates the female with sperm stored in his palps. At any time during the mating process, the female may interrupt Widow spiders produce a toxin that the family to learn about black widows and attack the male. However, males are affects the nervous system (neurotoxin). so that they can be readily identified and rarely attacked and eaten if the female is Muscle and chest pain or tightness are avoided. It is also a good idea to wear gloves well fed. Under natural conditions, the some of the most common reactions to the and a long-sleeved shirt when working in males often live around the periphery of the widow toxin. The pain may also spread to spider infested areas. female web and may feed on food that she the abdomen, producing stomach cramping Insecticides can be useful for adult has captured. These males may live longer and nausea. Other general symptoms spider control but are not particularly than those not associated with a female’s include restlessness, anxiety, breathing and effective against the eggsacs. Physical web. If eaten by the female, the male speech difficulty, and sweating. Swelling search and removal of widows is the most spider provides a good source of nutrients, may be noticed in extremities and eyelids, effective treatment. Insecticides can be used particularly proteins, which are used to help but rarely at the bite site. A sense of burning to reduce spider migrations into homes by produce and mature eggs. in the soles of the feet is often noted. spraying around the exterior foundation Widow spiders get their common Often there is a general sense of and lower story windows. This should be name because they are shiny black when discomfort shortly after the bite, and acute done before cold weather forces spiders full grown, and black is a traditional color symptoms increase in severity during the (and many insects) into homes to seek of mourning. first day. Symptoms usually decline after 2 shelter. However, the benefit from such to 3 days but some may continue for several treatment will be short-lived. weeks up to a month after the bite. Presently, various pyrethroid Widow Bites Other mammals vary in their reaction insecticides (bifenthrin, cyfluthrin, All members of the genus Latrodectus to widow toxin. For example, horses are permethrin, tetramethrin) are sold for are potentially harmful to humans. highly susceptible whereas rabbits are more general control of spiders around a home. However, the western widow is not resistant. Cats may be sensitive to a widow These have some residual effectiveness of aggressive and bites are very infrequent bite while dogs reportedly suffer only several weeks, particularly if not exposed even when large numbers of spiders occupy mild symptoms. to light and moisture. For control of the an area. The adult female spiders usually western widow these should be applied remain in their webs unless forced out by to specific areas most likely frequented by adverse temperatures or destruction of their Management widows – dark, undisturbed sites where web. They do not forage for food and the Many insects prey on widow spiders flying insect prey may occasionally pass. insects they eat are caught in the webs and including mud dauber wasps, other spider- However, physical removal or killing of eaten at the site. Widow spiders rarely, if hunting wasps, and other spiders. A species the adults and crushing or freezing eggsacs ever, bite when not within a web. Bites may of frit fly (Chloropidae) and parasitic (leave in the freezer for several weeks) are be more likely if the female is tending an wasps develop on the eggs of the spider. more effective treatments. egg sac in the web, which she will defend. Small rodents may feed on black widows, A large number of controls are Widow bites are nearly always from although the sticky silk that the spider sometimes promoted for control of spiders, female widows. Male widows, are less likely produces often discourages these predators. including widows. These include various to be encountered than females. Being Periodically check areas in and around chemical repellents (e.g., mock orange, smaller than the females, they have smaller the home where widows may likely occur. garlic) or ultrasonic frequencies – neither venom glands and smaller fangs; thus, it is Widow spiders prefer to nest near the of which spiders perceive or respond unlikely that males, even if encountered, ground, in dark, undisturbed areas. Nest to. Because of their complete lack of could penetrate the skin of an adult human. sites are often near holes produced by small demonstrated effectiveness, the promotion Even female spiders are timid and not likely animals or around construction openings for sale of such products is considered to bite unless seriously provoked. Most and wood piles. Low shrubs are also fraudulent and illegal under Colorado law. bites occur when people inadvertently press common sites for widows. Indoors, widows down on a spider resting under a rock, similarly occur in dark, undisturbed under wood in a wood pile, or, in the days sites such as behind furniture or under of outdoor privies, when people used the desks. Undisturbed basement areas and facilities and did not see a spider resting crawl spaces of homes are also commonly on or near the seat. Widow spiders have to colonized by widow spiders. be provoked in a highly specific manner in When discovered they can be most order to induce them to bite a human. effectively destroyed by crushing or Widows, and other spiders, bite using vacuuming the web and spider, using a pair of fangs on their jaws, or chelicerae. protective methods (e.g., wear heavy, The bite can go unnoticed, although it most leather gloves). Spiders can also be often produces an immediate sharp, pin- discouraged by increasing the lighting of prick pain. A slight swelling and redness darkened corners, such as by appropriate may soon develop at the bite site. furniture arrangement or the use of Colorado State University, U.S. Department of artificial lighting. Encourage everyone in Agriculture and Colorado counties cooperating. CSU Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.