Brown Recluse

The Brown Recluse, Loxosceles reclusa, is without question the most infamous spider in the United States. Frequently maligned as the cause of serious necrotic wounds, and often confused with many harmless species, its reputation is inflated far beyond reality.

Identification

Also known as the “fiddleback” and “violin spider,” Loxosceles reclusa is usually marked distinctively on the carapace. This dark, violin-shaped marking may be vague, or even absent; and many other spiders have similar contrasting patterns. The only way to positively distinguish Loxosceles species is by their eyes. Brown spiders have only six eyes, compared to the usual eight eyes most spiders have. This sextet of ocular organs is arranged in a triangular pattern of three pairs. Understandably, most people don’t want to get close enough to a spider to see its eyes, but that is what is necessary to confirm an identification. Many other spiders are similarly colored, and of similar size. Recluse spiders attain a body length of 5-13 millimeters, with a legspan up to 30-40 millimeters.

Geographic Range

The Brown Recluse is native only to the central and southeast U.S., from Texas to northern Georgia, southeast Nebraska, southwest Ohio, and states in between. There are twelve other species of Loxosceles in North America, two of which are accidental introductions from other parts of the world. The Chilean Recluse, L. laeta, is found in only a few old, historical buildings in greater Los Angeles. The Mediterranean Recluse, L. rufescens, has turned up in many large urban areas, but is again usually restricted to a few highly localized populations. The remaining ten Loxosceles species are confined to the southwest U.S., from south Texas to southeast California and southern Nevada, and are found outdoors more often than in dwellings and other structures. While it is possible for any of the brown spiders to be transported outside their normal geographic range via commerce or travel, the Brown Recluse is less likely to spread than the foreign species.

Bites

The medical significance of the Brown Recluse has been sensationalized by the media and the internet. Various websites display graphic images of the most extreme cases of envenomation, if the pictures even represent spider bites at all. Yes, the venom of Loxosceles is cytotoxic (destroys tissues), and can produce necrotic wounds in some bite victims. However, many other maladies can express similar symptoms. MRSA (Methicillin-resistant Staphylococcus aureus) is one of these. More to the point, spider bites in general are a rare phenomenon. They are simply overdiagnosed. You owe it to yourself to read this article by Dr. Richard Vetter, and insist that your physician rule out those other potential causes if you ever present what you believe is a “spider bite.”

Should you ever present with a suspected or confirmed spider bite, run, don’t walk, away from any physician who applies electric shock to “deactivate the enzymes in the venom.” This is not a practice endorsed by any respected body of doctors, yet I personally know one bite victim in a rural area who received such “treatment” back in the year 2000.

Precautions

It is relatively easy to avoid the prospect of a spider bite by taking simple precautions, such as those outlined in this article from Spiders.us. Simply never put your hands in places you can’t see. Do be careful moving items that have been stored for lengthy periods without disturbance, especially clothes and linens, as spiders frequently hide in garments and blankets. One of the specimens depicted here was in the folds of a blanket that was taken out of storage in a home in Leavenworth, Kansas.

Natural History

The Brown Recluse earns its name for its shy nature. They hide in narrow cracks and crevices, under stones or other objects, from which they spin a thin, haphazard, vaguely sheet-like web. Sometimes they wander out of their snares, especially at night. They are surprisingly tolerant of others of their kind, so large populations may occupy a small area. The family living in one home in Kansas City, Kansas collected 2,055 specimens in only six months. No one in the household was ever bitten, either. Individual recluse spiders in captivity live 2-3 years.

Conclusions

You should really not fear the Brown Recluse, but do give it respect. Exercise caution in places that you do not visit frequently, like the storage shed, cellar, deep recesses of the garage, and similar structures. Do not assume that every spider you see is a recluse. Male spiders of nearly all species, including those normally confined to webs, will wander in search of mates and may stray indoors in their quest for love. Should you really be concerned, take the specimen to an entomologist or arachnologist at a university, natural history museum, or even the public health department to have it properly identified.

Sources: Bradley, Richard A. 2013. Common Spiders of North America. Berkeley: University of California Press. 271 pp.
Forks, Thomas P. 2000. “Brown Recluse Spider Bites,” J. Am. Board Fam. Med. 13(6): 415-423.
Kaston, B.J. 1978. How to Know the Spiders (3rd edition). Dubuque, Iowa: Wm. C. Brown Company Publishers. 272 pp.
Vetter, Rick. 2004. “Causes of Necrotic Wounds other than Brown Recluse Spider Bites,” UCR Spiders Site. University of California-Riverside
Ubick, D., P. Paquin, P.E. Cushing, and V. Roth (eds.). 2005. Spiders of North America: an identification manual. American Arachnological Society. 377 pp.

"Is it poisonous?"

Hardly a day goes by when I am not asked some version of this question. Maybe it is phrased “Is it dangerous?” or “Is it venomous?” This illustrates just how paranoid we have become of other life forms on this planet. Let’s clarify the definition of each of these terms, and the relative risks involved with each.

Most of the time, people use the terms “poisonous” and “venomous” interchangeably. What they usually want to know whether a given spider, scorpion, or insect is venomous. Venomous animals possess toxins that they deliver to a victim by biting or stinging. Nearly all spiders are venomous, as that is how they kill their prey. Only a handful of spiders are dangerously venomous to the average, healthy human being. Here in North America, the only spiders confirmed to be potentially dangerous are widows (genus Latrodectus), and brown spiders (genus Loxosceles). This is not to say that the bite from *any* spider cannot spark an allergic reaction in someone hypersensitive to venoms.

Western Black Widow (female)

What is generally exaggerated is the risk of being bitten by a spider. The likelihood of being envenomated by a spider is quite miniscule, especially if you take simple precautions like those suggested in this article at Spiders.us.

Some venomous insects can come as a surprise to the uninformed or uninitiated. Several caterpillar species, for example, have stinging spines or hairs that can cause excruciating pain, at least in some people. Be careful not to touch hairy or spiny caterpillars.

Flannel Moth caterpillar

Ironically, tarantulas in the genus Aphonopelma will kick tiny, barbed hairs off of their abdomen instead of biting in self-defense. The hairs become airborne and, if inhaled or otherwise contact mucous membranes, cause severe irritation or even allergic reactions. Some people who handle tarantulas, or even the molted exoskeleton, may pay for the experience with contact dermatitis.

Wheel Bug adult

Many species of ants other than fire ants are capable of stinging, as can “velvet ants,” wasps in which the female gender is wingless and may resemble a large, hairy, brightly-colored ant. Assassin bugs like the Wheel Bug, and aquatic bugs like giant water bugs (aka “toe-biters”), backswimmers, and water scorpions, have a venomous bite to immobilize prey, but they can bite in self-defense, too. I can speak from experience that it is not pleasant.

Giant Centipede

Centipedes, fast-moving, snake-like arthropods with “too many legs,” are venomous, their first pair of legs modified into fangs they use to subdue their prey or defend themselves. Scorpions, arachnids related to spiders have a venomous stinger at the end of their telson (“tail”), but only the “bark scorpion,” Centruroides sculpturatus, is dangerously venomous. It occurs only in Arizona, western New Mexico, southern Nevada and Utah, and extreme southeast California.

The term poisonous means that an organism is toxic if ingested (swallowed). A startling number of insect species actually are poisonous and it pays to learn which ones, especially if you have curious toddlers prone to putting things in their mouths. Fireflies are very poisonous, as their bodies contain lucibufagins, toxins closely related to the toxins in toads.

Blister Beetle, one of many species

Blister beetles (image above) are aptly-named, for when molested they ooze a liquid substance containing cantharidin, an irritant that can raise blisters on sensitive skin. Even worse, if eaten, they can be lethal. Ranchers must be careful that blister beetles are not accidentally baled in hay. Horses that swallow beetles along with hay can die.

Millipedes, slow-moving, worm-like arthropods with lots of legs, are vegetarians, but most can defend themselves with harsh chemical secretions. Some species, like the one shown below, ooze cyanide compounds to repel potential predators. Others produce substances that can stain, or even burn, the skin.

Flat-backed Millipede

Luckily, many venomous and poisonous insects and spiders are aposematic. That is, they are marked with bright, contrasting “warning colors” such as black and yellow, orange, or white. There are many completely harmless insects that mimic those dangerous species, but when in doubt it pays to avoid handling brightly-colored animals.

While I do want people to find fascination in insects, spiders, and other invertebrates, I also want the public to stay safe and healthy. Be careful out there.

Spider Scare in the News

Last week a news story broke about a potentially dangerous neotropical (New World tropics) spider that stowed away in a crate of bananas from Latin America and ended up in a grocery store in Tulsa, Oklahoma. Credit the media for sticking with the story and getting it right for a change, successfully quelling what could have been needless widespread public hysteria.

Two experts in the case contradicted each other’s identification of the arachnid, and because the specimen was dispatched, there was no way to verify its identity. There are several species in the spider family Ctenidae, collectively known as “wandering spiders” because they do not spin webs to catch prey. Their large size and often aggressive behavior is enough to intimidate a person, regardless of how venomous they may be. The genus Phoneutria includes at least some species that can, rarely, deliver a lethal bite. Species in the harmless genus Cupiennius, however, can be easily mistaken for their deadlier cousins.

Richard S. Vetter and Stefan Hillebrecht addressed this dilemma in the cover story of the summer, 2008 issue of American Entomologist, a journal of the American Entomological Society. The bottom line from the article is that without close examination of a specimen, it is unlikely that an individual spider can be correctly identified. The better news is that fatalities from bites of Phoneutria are very rare, even for “at risk” populations such as the elderly and infants. It is largely one’s immune system response, rather than the toxicity of venom, that determines whether a bite will result in no reaction, a mild response, or a severe trauma.

Many of the reader response comments on the Yahoo version of the story centered on the perceived failure of our government inspection services. Dangerously venomous tropical spiders do not routinely infiltrate our nation, however, and the large volume of foreign shipments to the U.S. precludes comprehensive inspections. It is the price we pay for a “free market” where goods pass unfettered across borders. Collectively, through our demand for tropical fruits and houseplants, we consumers have determined that risks like spiders are an acceptable hazard.