Bug Proof Your Home from Venomous Spiders

Pest Management In and Around Structures September 10, 2015 Print Friendly and PDF

Door threshold.

Spiders are predators that feed on insects and other arthropods. Most often they are quite beneficial to our environment, and are harmless. In the United States,  about 6,000 species have been identified and only two groups occasionally are harmful to humans. Recluse and widow spiders have been associated with significant pathology and very rare reports of death.

First we are going to talk about the types of venomous spiders that you might encounter in the North America, then you can follow these tips to help keep these venomous spiders outside in nature and out of the spaces that we work, live and play. In the case of a spider bite, contact a physician or your state Poison and Drug Information Center as soon as possible for advice and assistance. If possible, collect the spider to aid diagnosis and correct treatment procedures.

The Recluse Spider

The recluse spiders (Loxosceles spp.) are often mistakenly referred to as brown recluse spiders; the brown recluse actually refers only to one species. Adult recluse spiders are brown in color and the body is about a half an inch long. Their legs are long and delicately covered with short, dark hairs. The leg span is about 1 1/2 – 2 inches as adults.

Distinguishing characteristics include three pairs of eyes arranged in a semicircle on the top of the cephalothorax (combined head and abdomen) and a violin-shaped marking immediately behind the eyes in some species. This marking also gives them the name “fiddleback” or “violin spider” although the violin marking is faint or missing in some southwestern species.

Most recluse spiders are found living in large numbers in human structures. Males, females and even spiderlings are capable of venomous bites occasionally creating a disease state now known as necrotic arachnidism.

The bite itself is often unnoticed and the severity of the reaction varies greatly between individuals. In the rarely-exhibited case of necrotic arachnidism, the bitten area becomes painful, swollen and blistered within hours. This site will evolve into what has classically been described as a bulls-eye lesion with a dark center (dead skin) outlined by white and set on a red and inflamed background. It is several weeks before the blackened area falls away, leaving a pit of scar tissue. On rare occasions, the response involves a large amount of tissue destruction and a serious life-threatening systemic reaction.  Medical care for most recluse bites is simply rest, cold compresses and neutral position of the patient.  More extreme reactions may require surgery.

Brown recluse spider.
Brown Recluse Spider

The Black Widow

Ventral view of a black widow spider.

The common “black widow” spider specifically refers to the eastern species Latrodectus mactans. Our widow species Latrodectus hesperus is however very similar in appearance to the true black widow. The female is  toxic and males much less so due to their small size and weak jaw musculature. Females are shiny black and about 1.5 inches long. The famous characteristic mark is the reddish hourglass shape on the underside of her abdomen.

Like the recluse spider, the bite itself is not terribly painful, but local pain does follow very shortly after. The venom can cause abdominal pain similar to appendicitis as well as pain to muscles and the soles of the feet. Other symptoms include alternating salivation and dry-mouth, paralysis of the diaphragm, profuse sweating and swollen eyelids. Most healthy people recover rapidly in two to five days but the rare fatalities that occur are due to heart and lung failure.

If bitten, clean the site well with soap and water. Apply a cool compress over the bite location and keep the affected limb elevated to about heart level. Ibuprofen or acetaminophen may be taken to relieve minor symptoms.

Female black widow spider.
Black Widow Spider

 

Tarantula

Black widow spider female.Tarantula spiders belong to the family Theraphosidae. They are our largest spiders. The males can reach a length of 2 to 2 ½ inches and the female 4 inches. These spiders feed on arthropods and small vertebrates such as mice, lizards and snakes. Females can live as long as 20 years. All species are nocturnal, living in burrows that they construct. During our late summer months, the males are seen moving through the desert in search of mates. Tarantulas are usually very timid and secretive but when threatened they can bite. They have large fangs that can cause pain. Their venom is usually harmless to humans. Another method of defense is using the hind legs to rub hairs off the top of the abdomen. This cloud of fine hairs can be irritating to the eyes and mucus membranes so be careful when handling these spiders.

11 Tips to Help You Bug Proof Your Home From Spiders

  1. Perform routine, thorough house cleaning, particularly storage areas (closets, basements, attics, etc.) and behind outside shutters. Regular dusting and clutter reduction removes hiding places. Pay particular attention to doors, windows, vents and along foundations.
  2. Reduce clutter in garages, attics, and basements.
  3. Reduce clutter in storage cupboards; do not place your hands where you cannot see what you are picking up.
  4. Trim weeds around the building foundation and remove firewood, building materials, and debris to discourage insects and spiders from living next to a structure. Reduction of heavy dense vegetation will help reduce spider populations.
  5. Install tight-fitting window screens and door screens.
  6. Consider installing yellow or sodium vapor light bulbs outside entrances because these lights are less attractive to insects and thus draw fewer spiders to the area.
  7. Follow the guidelines for general exclusion e.g., sealing cracks, fitting door sweeps and eliminating other possible entry points to prevent spiders from moving indoors.
  8. Use a vacuum to remove webs, unwanted spiders and egg sacs on a continuous basis.
  9. Learn to recognize recluse and widow spiders and instruct other members of the household.
  10. Do not collect wood from woodpiles out-of-doors without wearing gloves. Place wood from outside directly on fires. Do not store indoors.
  11. Chemical control need only be considered if there are a number of bites reported in the area and occupants are at risk. The widow spider is resistant to many insecticides so check the label. However, recluse spiders and widow spiders can simply be vacuumed. A small amount of boric acid crystals can be vacuumed up prior to cleaning out spiders and webbing. To be extra careful, remove the vacuumed bag and discard in an outside garbage container immediately after vacuuming.

 

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.