The Brown Widow

Scientific Name:  Latrodectus geometricus

Size:  The average size of mature, female Brown Widow spiders is approximately .5 inch, with a leg span of 1.5 to 2 inches. Mature, male Brown Widow spiders are much smaller – Approx. 1/3 the size of the female.

Description:  Brown Widow spiders are typically tan to medium brown in color. In some instances, they can be significantly lighter, almost cream colored, while in others they can be much darker brown, almost appearing black. They have the typical widow hourglass marking on the underside of their abdomen, and most of the time this hourglass appears to be orange, sometimes yellow, on the Brown Widow instead of the red color typically found on the related black widow species. The top of Brown Widow's abdomen can vary greatly in the way it is marked. Typically it has red or white spots running down the middle of its back. Sometimes it will also have black and white markings patterned down the sides of the abdomen. The legs of the Brown Widow are typically banded with yellow/brown and black, as can be seen in the photos below, although I have found that this banding is very hard to see unless the spider is in bright lighting. When not in bright lighting, the legs appear dark brown or black.

Description Note: Female Brown widow spiders are gray to brown in color with white and black markings on the top surface of their bulbous abdomens.  The hourglass marking on the under surface of the abdomen is yellow to orange, and the legs have dark bands. 

Male Brown Widows: In contrast to the female, retains the coloration of the juvenile. After it matures, it stops eating, and its abdomen shrinks, because its only task at that point is to mate. The male still retains its one longitudinal stripe and set of three diagonal flank stripes on each side the abdomen. The males are much smaller than the females in body length although sometimes their legs are almost as long as the adult female.

Caution:  This species is found in urban areas and may be encountered around the home including: under roof eves, under railings on porches, in abandoned cars, under unused flowerpots, in piles of firewood, and under outdoor chairs.

Range:  The Brown Widow is an introduced species in the United States, and was once only found in central and southern Florida. It has since rapidly expanded its territory and is now found in every southern state in the United States. Outside of the United States, it is believed to live in most tropical areas of the world.   Its habitat ranges from British Columbia to Mexico and throughout the Rocky Mountains to the western portions of the Great Plains.
 

Important Notes:  As with all widow spiders, only the female of the species is considered dangerous. The much smaller male is considered harmless. Brown Widow spiders are nocturnal, which means they are active during the nighttime. They spend most of their time hanging "upside down" in their web, which often makes the hourglass marking immediately visible. Brown Widow spiders are very common around residential areas and often build webs on outdoor patios, patio furniture, outdoor grills, sheds, undersides of decks, and in garages.

Brown Widow spiders are typically not aggressive, and bite as a defensive measure when they are attacked or feel threatened. They will often retreat into hiding, but are more protective of their web when there are egg sacs present.

The Web:  The web of the Brown Widow does not resemble the typical spider's web, such as the garden spider's web, that is often associated with spiders. It instead resembles a cobweb, constructed of very strong white silk. The web will often be constructed under rocks or logs, in sheds, barns, or in large cracks and crevices, where it will be dark and the web will be protected from the weather. The Brown Widow, being common around residential areas, will also build it's web under outdoor patio furniture, grills, pottery, and other stationary items that could provide shelter.

The web doesn’t have a very recognizable pattern although it does have vertical support threads above and below the central areas where the spider sits while it waits for prey at night. The lower support threads also alert the widow to the presence of a prey item blundering into the web. In most cases the widow spider will seek a retreat near the ground as the home base for her web, which connects to the retreat, allowing the spider to emerge to catch both flying and crawling prey at night. However, some spiders will make a retreat well above ground level, such as in the eave of a house, and then drop down 10 or more feet before building their web. Widow spiders come out at dusk. After making improvements to their existing web, they take up a position in the middle, their underside facing upward, to wait for prey. Any large disturbance of the web that indicates something larger than a prey item causes the spider to quickly move toward the safety of its retreat. The silk of a mature widow is very strong; running a finger through the web that a large spider has made results in an audible ripping sound. During World War II, black and brown widow silk was used to make crosshairs for gun sights.

Eggs:  The egg sac of the Brown Widow is very unique and is an excellent identifying feature. As seen in the photos below, the egg sacs are a creamy-tan color. What makes them unique is the many "spikes" that appear on the egg sac. When baby brown widow spiderlings emerge from their egg sac, they have tan legs and tan cephalothorax, the body part to which the legs attach, while the abdomen is mostly white with a few black spots. As the spider grows, the background coloration of the abdomen becomes olive gray, and there is a longitudinal white stripe on the top of the abdomen and three diagonal stripes on the flanks with a small black dot at the uppermost portion of each diagonal stripe. Like all spiders, as the spiderlings grow larger, they molt in order to shed their restrictive exoskeleton. With successive molts in females, the white stripes become thinner, the olive gray darkens toward brown, and eventually the spider acquires its well-known light to dark drown coloration. Some mature females retain one or two conspicuous, indented white lines on the front surface of the abdomen that look like a corporal’s chevrons. In the youngest spiders, the space where the hourglass develops starts off being a whitish shield. As the spider grows and goes through several molts, the color of this shield turns from white to yellow to orange to red and changes from a shield with thick middle to a hourglass with a thin, tapered middle.

Habits:  The mature female of the brown widow spider is from 1 inch to 1 ½ inches long (with legs extended) and can live 1 to 2 years.  In her lifetime, she can lay 10 to 20 eggs sacs with each sac containing approximately 250 eggs.  The egg sac of the brown widow spider is white to tan in color and is covered with pointed projections, much like the seed of a sandspur.   The egg sac is ½ inch in diameter and is found attached to the web of the female.  The egg sac of the black widow, which is similar in color, has a smooth surface.

Young spiders known as spiderlings hatch in approximately 14 to 21 days but remain inside the egg sac for 4 days to one month.  After this time they emerge from the egg sac, molt and begin eating but remain in the nest area for several weeks. Eventually, spiderlings move away from the nest area by “ballooning”: a silk line released by each spiderling into the wind and the spiderling is carried off.  Females molt 6 to 9 times before reaching maturity, while the male brown widow molts 3 to 6 times before reaching maturity.  Males are much smaller than the female (1/2 to 3/4 inch long, with legs extended), do not live as long as the female, and have not been recorded to bite. All widow spiders are shy and will try to flee rather than bite a human.  Cases of widow bites occur when a spider is pressed against the skin of a person (when putting on clothes or shoes) or when a hand is reached into dark areas where the spider is present. It has been reported that the venom of the brown widow is as toxic as the black widow spider, but they are less likely to bite and do not defend their webs as vigorously as black widows.

Control:  As with black widow spiders, brown widow spider control requires sanitation and elimination of nesting sites.  Inside the house, garage, and porch, brown widow spiders, their egg sacs, and webbing should be removed with a vacuum cleaner.  After cleaning, the bag should immediately be removed, placed in a sealed plastic bag, and disposed of in outdoor trash bins.  As an added precaution, bags containing spiders and egg sacs can be placed in a chest freezer for several hours.  Regular inspections and routine cleaning (wearing gloves) of the areas the spiders have been previously found should occur in and around the home. Areas with excess clutter should be eliminated, as this will discourage spiders from nesting.  Empty containers outside the home (flowerpots, buckets) and firewood should be moved away from the house or removed.  Cracks, holes, and spaces around doors and windows should be sealed.  If spiders remain after sanitation and elimination of nesting areas, insecticides may be required.  Treatment with aerosol sprays containing insecticides labeled for spiders will kill spiders when directly applied to them.  Spot treatment with insecticidal dusts in cracks and crevices where spiders build their webs may also help with control.

Medical Aspects

The bite of the brown widow is much milder than the western black widow. In one study in Africa, where the brown widow might have originated, the most common symptoms in 15 verified bites were that the bite hurt when it happened, and it left a red mark; none of these patients developed the typical dynamic symptoms of black widow envenomation. However, there is one American record of a verified bite where the patient developed more severe symptoms and required hospitalization. Although its venom is as potent as black widow venom, drop for drop, the brown widow probably doesn’t inject very much venom during a bite, making it much less dangerous than the native black widow spider.

The False Widow Spider: The false black and brown widow, (Steatoda grossa), is not a true widow spider; however, it is in the same family, Theridiidae, as the widow spiders and easily can be confused with them. It shares the same rounded-abdomen body form and web-making traits. It is slightly smaller than a mature western black widow spider, is chocolate brown, and never has red coloration on its belly. The false widow is a European immigrant that has become extremely common in Pacific Coast homes from San Diego to British Columbia. It doesn’t seem to need as much food as the black widow, so the spiders are more likely found inside cupboards and underneath refrigerators or cabinets. False widows make an egg sac that looks like a cotton ball with indistinct margins. Unlike black or brown widow spiders, baby false black widow spiderlings are dark like their mothers when they emerge. Because they are more common in homes, they frequently are involved in bite incidents. They have mild venom and cause symptoms similar to a mild black widow spider bite. When black widow antivenom mistakenly has been used on false black widow bites, it appeared to eliminate the venom effects.

MANAGEMENT

One of the easiest ways to minimize encounters with widow spiders is to reduce clutter around your home, which deprives them of places to make retreats. However, it is impractical to eliminate them completely by removing all clutter. Regularly vacuuming or sweeping windows, corners of rooms, storage areas, basements, and other seldom-used areas helps remove spiders and their webs. Vacuuming spiders can be an effective control technique, because their soft bodies usually don’t survive this process. In the garage, keep items such as gardening clothes and gloves in bags closed with zipper locks or twist ties. Store seasonal items such as winter clothes or Christmas decorations in boxes that you can tape shut and can place off the floor and away from walls in order to exclude spiders. When cleaning up clutter in garages and other storage areas, be sure to wear gloves to avoid accidental bites. Areas of concern include children’s pedal-powered toy vehicles made of molded plastic that have open spaces facing downward where spiders can crawl in. Picnic tables and other large pieces of furniture where you place your fingers underneath to lift also can be a source of exposure.

Spiders can enter houses and other structures through cracks and other openings. To prevent spiders from coming indoors, seal cracks in the foundation and other parts of the building and gaps around windows and doors. Good screening not only will keep out many spiders but also will discourage them by keeping out the insects they eat. However, baby black widows have no problem crawling through regular window screen mesh. Be careful that you don’t carry spiders indoors on items such as plants, firewood, and boxes. Stack woodpiles away from your house, and never pick up pieces of wood unless you are wearing gloves. Eliminate places for spiders to hide and build their webs by keeping the area next to the foundation free of trash, leaf litter, and accumulations of other materials. Removing ivy and other heavy vegetation growing around foundations and trimming plant growth away from your home and other structures will discourage spiders, in general, from taking up residence near the structure and then moving indoors.

Outdoor lighting attracts insects, which in turn attracts spiders. If possible, keep lighting fixtures off structures and away from windows and doorways. Sweep, mop, hose, or vacuum webs and spiders off buildings regularly. Insecticides won’t provide long-term control, so generally you shouldn’t use them against spiders outdoors. Because widow spiders are nocturnal, a nonchemical method of eradication is to search for them at night with a flashlight and kill them with a shoe or rolled up newspaper. If you are concerned about wildlife and feel comfortable doing so, you can remove individual spiders from indoor areas by placing a jar over them and slipping a piece of paper underneath to seal off the opening when you lift the jar up. Release the spider about 100 feet from your home into a natural area.

One aspect that makes controlling widow spiders difficult is that they, like many spiders, exhibit a behavior called ballooning. When the spiderlings are very small, on warm days when there is an updraft they climb to the top of a fence post or piece of vegetation, raise their abdomens into the air, and release a small filament of silk. When the updraft currents overtake the forces of gravity, the spiderling is carried into the air to another location. This may only be a few feet away, or it could be miles. Ballooning spiderlings have been captured at 10,000 feet from the ground and 200 miles offshore. Because spiderlings will be dropping down on your property continually, eliminating them will be a task that needs to be done repetitively throughout the year.

And finally, the Chemical Control Option: Typically pesticide control of spiders is difficult. Various insecticides are registered for control of spiders including pyrethrins, resmethrin, allethrin, or combinations of these products; however, they usually aren’t very effective. Sprays work only if you apply them directly to the spider or their web, since the spray residual does not have a long-lasting effect. This means a spider can walk over a sprayed surface a few days—and in many cases, a few hours—after treatment and not be affected. Sprays won’t affect egg sacs, and if you apply them to the outside perimeter of a structure, they won’t keep spiders from moving in. Control by spraying is only temporary unless accompanied by housekeeping. It is just as easy and much less toxic to crush the spider with a rolled up newspaper or your shoe or to vacuum it up. Removing harborage sites such as clutter, woodpiles, or heavy ground cover is essential for reducing widow spider populations. Sticky traps offer a non-insecticidal way to remove spiders from your home as long as you can place the traps where pets and curious children can’t tamper with them.

Note:  This is the fifth in a series that I am doing on Spiders, enjoy - Bird