By Fred Santana, Ph.D., Sarasota County IPM Educator
When the subject of dangerous spiders comes up, the average person usually thinks about the black widow spider. Their shiny black body with a prominent red hourglass marking on the underside of the abdomen is an image that readily comes to mind.
DISTRIBUTION In Florida, however, there are three other venomous widow spiders (Southern black widow, northern black widow, and, the red widow) in addition to the brown widow. The most commonly encountered species of the group that people are finding around their homes and work place in Sarasota County is the brown widow spider, Latrodectus geometricus. In the mid to late nineties there seems to have been an outbreak of brown widow spiders. Since this article was first written in 2000, this spider has spread throughout Florida and people have reported sightings of it from Southern California, Colorado, Texas, Arkansas, Mississippi, Alabama, Georgia, and South Carolina. Complaints about its occurrence in cars and RVs indicate this spider will make it home in these sites. Cars, trucks, and RVs have probably helped to distribute this spider far and wide. It rapid expansion in Florida in the late 90s may have been the result of the milder winters. However, the most important factor in its expansion has probably been transportation by vehicles. The Extension Office continues to receive complaints asking how to rid them from in and under cars
APPEARANCE Because they vary from light tan to dark brown or almost black, with variable markings of black, white, yellow, orange, or brown on the back of their abdomens, brown widows are not as easy to recognize. The underside of the abdomen, if you can see it, contains the characteristic hourglass marking. Unlike the black widow, the hourglass is orange to yellow orange in color. The following photographs show the hourglass marking under the abdomen and the variety of color phases this spider exhibits.
Light tan abdomen with distinct markings
Light brown abdomen with distinct markings
Light tan abdomen with vivid markings
Brown widow with webbing
BITE RISK Although the bite of a widow spider is much feared, the widow spiders are generally non-aggressive and will retreat when disturbed. Bites usually occur when a spider becomes accidentally pressed against the skin of a person when putting on clothes or sticking their hands in recessed areas or dark corners. According to Dr. G.B. Edwards, an arachnologist with the Florida State Collection of Arthropods in Gainesville, the brown widow venom is twice as potent as black widow venom. However, they do not inject as much venom as a black widow, are very timid, and do not defend their web. The brown widow is also slightly smaller than the black widow.
HABITAT The brown widow builds its web in secluded, protected sites around our homes, often very near our presence. It has a fondness for buildings but will construct its web in all kinds of man-made structures, and even vegetation. Some typical sites include inside old tires, empty containers such as buckets and nursery pots, mail boxes, entry way corners, under eaves, stacked equipment, cluttered storage closets and garages, behind hurricane shutters, recessed hand grips of plastic garbage cans, undercarriages of motor homes, underneath outside chairs, branches of shrubs. The following photographs show some sites where brown widows have constructed their webs.
SANITATION (PREVENTIVE CONTROL) Sanitation is the most important strategy in reducing widow spiders infestations around the home. Routine cleaning is the best way to eliminate spiders and discourage their return. Gloves should be worn if you suspect widow spiders to be present. Reducing clutter makes an area less attractive to spiders. Inside a home or garage, a thorough cleaning with a vacuum cleaner is an effective way to removes spiders, their egg sacs, and webbing. When vacuuming, the vacuum bag should be removed when you are finished and placed in a sealed plastic bag for disposal. This should be followed by regular inspections to insure they have not returned. Outside the home, potential hiding places such as firewood, building materials, and other debris lying on the ground should be moved away from the building or disposed of. Any cracks, holes, or spaces around windows and doors should be sealed or fitted with weather stripping.
INSECTICIDAL CONTROL If a spider problem still exists after sanitation work, insecticides may have to be used. Direct contact with a non residual aerosol spray will remove live spiders when a vacuum is not available. Spot treatment applications of a residual insecticide to locations where spiders build their web sites can be helpful to prevent new spiders from becoming established. Although reduction of outdoor harborages and sealing of cracks and holes is the best approach to preventing spiders, insecticidal dust followed by sealing of cracks will reinforce exclusion. Where it is not feasible to vacuum, such as outdoors, an insecticidal dust can be very effective. Dr. Philip G. Koehler, University of Florida, reports that dusts cling to webs for long periods. When spiders reportedly chew their webs to recycle silk, they consume the toxicant and die. Where spiders are very numerous, a spot treatment of a residual insecticide to small areas can be effective. Perimeter sprays around the foundation may provide some relief but rapidly degrade due to sunlight, and do not minimize pesticide exposure to people and nontarget organisms.
Habitat – brown recluse is found in the United States from the east to the west coast, with predominance in the south.
Spider Identification – an adult spider is 1/4 to 3/4 inch in body – a dark violin shape is located on the top of the leg attachment region with the neck of the violin pointing backward toward the abdomen. Unlike most spiders that have 8 eyes, the brown recluse has 6 eyes arranged in pairs – one pair in front and a pair on either side.
CLICK HERE - FIRST AID – Brown Recluse Spider Bite
Only a small amount of venom can cause serious illness, as the poison attacks the nervous system. Systemic envenomisation usually results in headache, nausea, vomiting, abdominal pain, pyrexia and hypertension.
The pain around the bite area can be excruciating or it may go unnoticed. First aid and medical attention should be sought as soon as possible, if bitten. If you have heart condition or other heart problem, you may need hospitalization.
Spider Identification – the body of an adult black widow is about 1/2 inch long. The female black widow is normally shiny black, with a red hourglass marking on the underside of the abdomen. The marking may range in color from yellowish orange to red and its shape may range from an hourglass to a dot.
Habitat – prefers woodpiles, rubble piles, under stones, in hollow stumps, sheds and garages. Indoors it can be found in undisturbed, cluttered areas in basements and crawl spaces.
CLICK HERE - FIRST AID – Black Widow Spider Bite
Spider Identification – they are brown in color and the adults measure roughly 1/3 to 2/3 inch in body length and 2/3 to 2 inches in leg span. Their abdomens have several chevron shaped markings. Males are distinctively different from females in that they have two large palpi (mouth parts) that look like boxing gloves. Females tend to have a larger and rounder abdomen when compared to males.
Habitat – they can be found anywhere in Washington, Oregon, Idaho, Montana, Wyoming, Utah and Colorado. They rarely climb vertical surfaces and are uncommon above basements or ground level.
CLICK HERE - FIRST AID – Hobo Spider Bite
Spider Identification – are common outdoors and are occasionally found indoors. They are generally brownish or grayish with light and dark stripes near the head. They have long spinnerets and are moderate-sized (3/4 inch long). Grass spiders construct a large sheet web with a funnel they use as a retreat. These webs are commonly built on the ground, around steps, window wells, foundations, and low shrubs.
Habitat – These spiders are often called grass spiders because they construct their webs in tall grass, heavy ground cover and the branches of thick shrubs. Rarely will a funnel web spider be seen indoors, except for an occasional wandering male. They are found mostly in the Pacific Northwest states.
CLICK HERE - FIRST AID – Funnel Web Grass Spider Bite
Spider Identification – a medium to large spider of up to 1 and 1/2 inches in body length. The male Mouse Spider often has a bright red head and elongated fangs.
Habitat – Mouse spiders are ground dwellers with burrows of more than 3 feet deep. The male often wanders about during the day on open ground, especially after rain, in search of females.
CLICK HERE - FIRST AID – Mouse Spider Bite
Spider Identification – adults are about 1/2 inch in body length and of a dark brown to black velvet textured appearance.
Habitat – this spider spins a lacy, messy web and is prefers dry habitats in secluded locations. It is commonly found in window framing, under eaves, gutters, in brickwork, sheds, toilets and among rocks and bark. Electric lights attract their prey – moths, flies, mosquitoes and other insects.
CLICK HERE - FIRST AID – Black House Spider Bite
Spider Identification – an adult is 1/2 inch to more than 1 inch in body length – mottled gray to brown in color, with a distinct Union Jack impression on its back. The female carries it’s young on its back.
Habitat – this spider is a ground dweller, with a burrow retreat. It has a roving nocturnal lifestyle to hunt their prey and can move very rapidly when disturbed. Commonly found around the home, in garden areas with a silk lined burrow, sometimes with a lid or covered by leaf litter or grass woven with silk as a little fence around the rim of the burrow.
CLICK HERE - FIRST AID – Wolf Spider Bite
Spider Identification – an adult is about 1 and 1/2 inches in body length – brown to dark brown in color - heavily covered with fine hairs. The male has distinct boxing glove-shaped palps, that is, the two “sensory feelers” at front of its head.
Habitat – this spider is a ground dweller, with a burrow retreat lined with silk of up to 10 inches in depth and around 1 inch in width – prefers nesting in drier exposed locations – often has a wafer-like lid on the burrow entrance. Trap-Door Spiders are commonly found in the drier open ground areas around the home.
CLICK HERE - FIRST AID – Trap Door Spider Bite
Spider Identification – an adult is about 2/3 to more than 1 inch in body length – has a bulbous abdomen – often colorful – dark to light brown pattern. The common Golden Orb-Weaver Spider has a purplish bulbous abdomen with fine hairs.
Habitat – often found in summer in garden areas around the home – they spin a large circular web of 6 feet or more, often between buildings and shrubs, to snare flying insects, such as, flies and mosquitoes.
CLICK HERE - FIRST AID – Orb-Weaving Spider Bite
Spider Identification – adult 1/4″ to 1/2″ in body length – abdomen striped yellow and brown – as illustrated. The St Andrews Cross Spider usually sits, upside down, in the middle of its web forming a cross – as illustrated.
Habitat – this spider is a web-weaver usually found in summer in garden areas around the home. It is considered beneficial as it spins a large web to snare flying insects, such as flies and mosquitoes.
CLICK HERE - FIRST AID – St Andrews Cross Spider Bite
Spider Identification – an adult varies greatly around 1/2″ in body length – has long legs – the diameter of an adult including legs may reach 2″ – the first 2 pairs of legs are longer than rear two – it is hairy – buff to beige brown in color, with dark patches on the body.
Habitat – a hunter that prefers to live under the flaking bark of trees, under flat rocks and under eaves or within roof spaces of buildings. The Huntsman Spider often wanders into homes and is found perched on a wall. It is a shy, timid spider that can move sideways at lighting-fast speed when disturbed.
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