Randy Jacobs, M.D. Patient Education

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Spider Bites

Brown Recluse, Black Widow, and Tarantula




Many different kinds of spiders live around homes and buildings. The vast majority are harmless, and in fact are beneficial, because they prey upon flies, crickets and other insects. One spider in the USA which is potentially dangerous is the brown recluse. The BROWN RECLUSE is more of a tan than the image shows, with a violin- shaped black mark on the front section of its body. The female's body is about 1/2 inch long and her legs about another 1 inch long, so she will be about a 2 1/2 inch spread. The male is smaller. Some people are hardly bothered by the bite, but others may suffer a severe rotting of flesh in the area of the sting and the rotting is difficult to stop. The sore starts out as a painful little pimple and has been known to become quite large over a long period of time and the poison can also cause kidney failure, so be sure to get medical help immediately. The RECLUSE is not really a recluse because where there is one, there may be more. They hide out in old wooden buildings, in stored clothing, in dresser drawers, in attics and in shoes. Scorpions do too, so it might be a good idea to always check out your shoes before putting your feet in them! Fortunately, this spider is relatively uncommon, and has markings that the lay person can use to distinguish it from other non-threatening species.

 Description and Habits

The brown recluse is about 1/4 to 1/2 inches in body length (most adults are about the size of a United States dime to a US quarter with legs extended). Coloration ranges from tan to dark brown, with the abdomen often darker than the rest of the body. The feature that most distinguishes the brown recluse from many other harmless spiders is a somewhat darker violin-shaped marking on top of the leg-bearing section of the body. The neck of the violin "silhouette" points towards the rear (abdomen) of the spider. Brown recluse spiders also have 3 pairs of eyes (arranged in 3 groups of two) rather than 4 pairs for most other spiders. This diagnostic feature requires use of at least a 10X hand lens. The brown recluse roams at night seeking its prey. During the day, it hides in dark niches and corners, where it may spin a poorly organized, irregular web. Eggs are deposited in 1/2 inch long off-white silken egg sacs, often appearing flattened beneath and convex above. It is shy and will try to run from a threatening situation but will bite if cornered. People are sometimes bitten while they are asleep because they roll onto a brown recluse spider while it is hunting in the bed. More often the victim is bitten while putting on a shoe or piece of clothing which a spider has selected for its daytime hiding place.


 Medical Significance

The bite of the brown recluse is usually painless until 3 to 8 hours later when it may become red, swollen, and tender. Later the area around the bite site may develop into an ulcerous sore from 1/2 to 10 inches in diameter. Healing often requires a month or longer, and the victim may be left with a deep scar. Prompt medical attention can reduce the extent of ulceration and alleviate other complications that may develop. It should be noted that not all brown recluse bites result in ulcerations or scarring. Spider bites are difficult to diagnose, even by physicians. Anyone bitten by a spider which is believed to be a brown recluse should try to collect the specimen and bring it to a qualified individual for identification. Positive identification by an expert will help the physician decide on the appropriate course of treatment.



Eliminating an infestation of brown recluse spiders involves two basic principles: First, involves altering the environment in and around a building to make it less attractive to spiders. Second involves finding and destroying as many spiders as possible. The following measures can be used to control all spiders, including the brown recluse. 1. Routine, thorough house cleaning is the best way to eliminate spiders and discourage their return. A vacuum cleaner or broom effectively removes spiders, webs, and egg sacs. 2. Spiders prefer quiet, undisturbed areas such as closets, garages, basements, and attics. Reducing clutter in these areas makes them less attractive to spiders. 3. Large numbers of spiders often congregate outdoors around the perimeter of structures. Migration indoors can be reduced by moving firewood, building materials, and debris away from the foundation. Shrubs, vines and tree limbs should be clipped back from the side of the building. 4. Install tight-fitting window screens and door sweeps to exclude spiders and other insects. Inspect and clean behind outdoor window shutters. 5. Consider installing yellow or sodium vapor light bulbs at outside entrances. These lights are less attractive than mercury vapor, fluorescent, or incandescent bulbs to night-flying insects which, in turn, attract spiders. 6. To further reduce spider entry from outdoors, insecticides can be applied as a "barrier treatment" around the base of the foundation. Pay particular attention to door thresholds, garage and crawl space entrances, including foundation vents. Sevin (carbaryl), Ficam (bendiocarb), Dursban (chlorpyrifos), or any of the synthetic pyrethroids are effective, but may need to be reapplied periodically throughout the summer. Wettable powder or microencapsulated, "slow-release" formulations are most effective. Longer-lasting liquid formulations of Dursban can be purchased by homeowners through some lawn and garden shops. The brown recluse may be found living indoors or outdoors. Thorough inspection of cracks, corners, and other dark, undisturbed areas with a bright flashlight will help determine the location and extent of infestation. Indoors, pay particular attention to basements, attics, crawl spaces, closets, under/behind beds and furniture, inside shoes, boxes of stored items, and between hanging clothing. Brown recluse spiders also may be found living above suspended ceilings, behind baseboards, and inside ductwork or registers. Another way to detect infestations in these areas is to install glueboards or sticky traps. These devices, designed to capture mice and cockroaches, can be purchased at grocery or farm supply stores. Placed flush along walls and in corners, glueboards and sticky traps are useful monitoring tools and will also capture large numbers of spiders. Brown recluse spiders also live outdoors in barns, utility sheds, woodpiles, and underneath lumber, rocks, and accumulated debris. To avoid being bitten, wear work gloves when inspecting inside boxes or when moving stored items. Removal of unnecessary clutter is especially helpful in making areas unattractive to these pests. Indoor infestations of brown recluse spiders also warrant treatment with insecticides. Insecticides should be applied into areas where spiders are living, making an attempt to contact as many spiders and webs as possible with the treatment. Spot treatment with synthetic pyrethroids such as Tempo (cyfluthrin) or Demon (cypermethrin) are especially effective. Most household insecticides with spiders listed on the label (e.g. Raid Max) will also kill spiders provided the spider is treated directly. In inaccessible or cluttered areas such as attics and storage sheds, total-release foggers or aerosols containing resmethrin or synergized pyrethrins will have a better chance of contacting spiders that are hidden. Severe infestations of brown recluse spiders require specialized skills, persistence and equipment to eradicate. In these situations, it would be prudent to call a professional pest control operator.

Black Widow

The BLACK WIDOW female is known for its red hourglass-shaped design on the bottom of its black tummy shown here, about 1/2 inch body and long legs. The body is like a shiny patten-leather ..I guess one would call it an exoskeleton.(?) The male is smaller and usually doesn't bite. There seems to be no localized symptoms when bitten, but the venom is a neurotoxin and affects the nerve functions throughout the body . Since there is little symptoms at the bite location, it is sometimes difficult to diagnose the nerve symptoms if you don't actually see the spider. There can be pain one to eight hours after the bite, heavy sweating, nausea and stomach cramps. A muscle relaxant is standard emergency room treatment. The black widow likes to hide under sticks and rocks or logs, and the seats in old outdoor toilets. She really is a widow, as when she mates with her male, she kills him and consumes his fluids. So... She becomes a widow and usually alone. Most black widows occur outdoors and are not aggressive unless confined or disturbed. Females are more likely to bite when guarding an egg sac. Reports indicate that mortality from bites is the result of 1% or less of the cases, usually occurring in very young or very old individuals. With healthy people, recovery is usually complete in 2-5 days. However, this spider is considered the most venomous spider in North America. Adult black widow spiders have shiny, jet black, rounded, globular abdomens with 2 reddish or yellowish triangles on the underside that form a characteristic hourglass marking. Adult female northern widow spiders are shiny black or brown-black with 2 reddish triangles on the underside, resembling a split hourglass. These spiders are about 1/2 inch long, not including the legs (about 1-1/2 inches when legs are spread). Adult males are harmless, about half the female's size, with smaller bodies, longer legs and usually have yellow and red bands and spots over the back as do the immature stages. Newly hatched spiderlings are predominately white or yellowish-white, gradually acquiring more black and varying amounts of red and white with each molt. Juveniles of both sexes resemble the male and are harmless.


Over the past few years, tarantulas have become acceptable pets now widely sold, traded and kept in houses, apartments, schools and dormitories. Occasionally, these very large, hairy spiders escape within a dwelling causing alarm and panic among those fearing spiders. Actually, most tarantulas are docile, non-aggressive and rarely bite. Bites are not considered dangerous and cause little lasting pain. Bites are no more painful than a bee sting, and its symptoms should be treated similarly. Some have a dense covering of special hairs on the abdomen, which, when dislodged, cause skin irritation. This irritation is mechanical rather than chemical in nature. The name tarantula has unfortunately become associated with several spider families, but most often is applied to the ones called the hairy mygalmorphs. Tarantulas have been much publicized in horror shows in movie houses and television shows due to their forbidding hairy appearance. The largest tarantulas are tropical with a body length of 3-1/2 inches and a leg span of 9-1/2 inches. The largest United States' species has a body length of 2 inches and leg span of about 6 inches. These spiders are stout-bodied and covered with hollow, needle-like barbed hairs, especially on the abdomen. When disturbed, the hind legs are used to scrape off and throw very fine (fiberglass-like) abdominal hairs in the direction of danger, resulting in a remaining bald spot. A bald spot may also occur on the abdomen prior to the shedding of the skin. Hairs may cause a skin rash, allergic reaction and possibly anaphylactic (severe and sometimes fatal) shock to certain individuals. A CDC report shows that in 1994, there were 9,418 spider bites reported in the U.S. with 82 (0.9%) of them being attributed to tarantulas. Spider bites are not required to be reported by law and these numbers are from people calling poison control centers for advice, so the actual number may be higher. While there is little or no documented medical evidence regarding the medical significance of tarantula bites, all tarantulas are venomous and their bite can cause local and systemic reactions. If you plan on keeping and especially handling tarantulas you should be familiar with some basic first aid procedures in the unlikely event of a bite. Reactions to venom will vary from person to person and are affected by a number of factors including the amount of venom injected, the size and general health of the victim, and the toxicity of the venom. It is estimated that 5% of people will have an allergic reaction to (any) venom and of that group a small percentage will develop anaphylactic shock. Localized Reactions: Following a tarantula bite expect, at the very least, to see some local reactions: Localized pain, Redness, Swelling, and Skin wheal at the bite site. Immediate treatment should be to wash the area with soap and water and apply cool compresses to the site. A paste made from baking soda and water and applied to the site may help decrease the severity of the local reaction. Topical cortisone or Benadryl creams may also alleviate some of the irritation. You should also observe for signs of an allergic and/or anaphylactic reaction. If you haven't had a tetanus shot in the past 5 years, contact your primary care doctor to decide whether you should receive an update. If you haven't had a tetanus in the past 10 years, now is a good time to get one. Suctioning style snake bite kits are considered ineffective at withdrawing venom from a site and under no circumstances should you attempt to suck venom out with your mouth. Over the next week or so be sure to keep the area clean and apply an antibiotic ointment such as Bacitracin, Neosporin or Polysporin and watch for infection. Common Signs of Infection The site becomes red and warm to the touch. Red streaks appear near the site. Pain or yellowish discharge comes from the site. Fever, chills, body aches. Bumps in the armpits or groin. Allergic Reactions: Allergic reactions and anaphylactic shock are primarily caused by the release of immunoglobulin E (IgE). This antibody mediates the body's allergic response by attaching to the body's mast cells, which stimulates the release of histamine and heparin. Histamine has many effects on the body including bronchoconstriction, vasodilation and increased gastric motility. While uncomfortable, these reactions serve to accelerate the deactivation and elimination of the allergen. The signs and symptoms of an allergic reaction include: Headache is a common complaint as are anxiety and restlessness. A rash or urticaria (hives) along with a warm or itchy feeling caused by dilation and increased permeability of the capillaries. Sneezing, coughing and/or wheezing are early signs that can potentially progress to neck and throat tightness. The gastrointestinal system responds aggressively to the release of histamine. Nausea, vomiting, diarrhea and abdominal cramps are all attempts by the body to rid itself of the offending toxin. Wash the bite with soap and water, and apply cool compresses. Minor reactions generally respond well to over-the-counter antihistamines such as diphenhydramine (Benadryl) and will usually resolve anywhere from a couple of days to more than a week. If you experience any chest tightness, difficulty breathing or a lot of hives, you should be evaluated by a physician. The physician may opt to give epinephrine 1:1000 which decreases the capillary permeability and opens the airways. Steroids may also be prescribed for long term maintenance. Steroids decrease inflammation by suppressing the body's immune response. If you have an allergic reaction, there is roughly a 60% chance of a similar or worse reaction if bitten again. Anaphylactic Shock: Anaphylaxis can best be described as a runaway allergic reaction. In an anaphylactic reaction the person's airway can be rapidly obstructed by swelling, the blood pressure can drop sharply and convulsions or cardiac arrest may ensue. This is a true medical emergency and the person must be transported to a hospital immediately, preferably by ambulance. DIAL 9-1-1, or the number used to activate your local emergency medical service. Treat the local reaction as discussed above. Keep the affected extremity lower than the level of the heart. You might also apply a constricting band between the bite and the person's heart. This should only be a bit tighter than a watch band to decrease the flow of lymph. Do not apply an arterial tourniquet! Persons predisposed to anaphylaxis may be wearing a medic alert bracelet or necklace and may carry a kit containing epinephrine 1:1000. The person and family members should be trained in the indications for and use of the kit. If someone is allergic to bee and wasp stings it's a safe bet that they will also have an adverse reaction from tarantula venom.