Threat Or Scapegoat?

Although some spiders are risks to public health, most spiders that occur in the U.S. are benign and pose more of a psychological and emotional threat than medical risk.

Spiders are often considered a public health concern. The much-maligned culprit is rarely seen inflicting a bite and it is basically impossible to prove spider participation as the cause of the malady. Although some spiders are threats to public health, most spiders that occur in the U.S. are benign and pose more of a psychological and emotional threat than medical.

A century ago, it was thought ludricrous that a small black spider with a red hourglass was able to sicken a large human, much less be deadly. With increased knowledge, it appears that we have become more aware of the health risks of spiders to the point of now overemphasizing their involvement as the explanation for mysterious wounds or conditions. Part of this is fueled by arachnophobia and the nocturnal and "nefarious" manner in which spiders make a living (sucking bodily fluids out of their prey).

In this article, I will first discuss spiders that are or have been implicated as medically important. Second, I will expound upon some of my research regarding alleged spider bites and the many conditions that are misdiagnosed as such. What I have found is that although it is almost universally accepted that spiders are everywhere inflicting bites, much of this information is based on unsubstantiated myths and presumptive medical reporting. As Mark Twain said, "The trouble with the world is not that people know too little, but that they know so many things that ain’t so."

BLACK WIDOW SPIDERS. The infamous black widow belongs to the genus Latrodectus. They are primarily tropical and worldwide; many species are feared by humans. Many spiders have the generalized pattern of shiny black body coloration with accents of red. The American species typically have only a predominant ventral red hourglass, whereas the Australian species also has a conspicuous dorsal longitudinal red stripe. The Mediterranean species has 13 red dorsal spots and no hourglass. Coloration makes most species easy to identify, however, immatures and males are usually striped with white and identification is more difficult. There are five species in the United States — three are widely distributed while one is a benign African immigrant established in Florida.

Black widows are nocturnal. Bites occur when a human traps the spider against flesh, e.g., people carrying firewood, moving possessions, putting on rarely worn clothing like work boots and gardening clothes. Currently, most widow bites occur on the extremities of the body, however, before indoor plumbing, significant numbers of bites occurred in outhouses.

The bite of a black widow is similar to a pinprick; the venom affects the nerve-muscle junction resulting in intense pain, rigid stomach muscles and localized sweating. At the bite site, there may be a small red mark or red streaks leading away from the wound. Most bites resolve in a few days. Antivenin is available but, in the U.S., is used only in extreme cases because of potential fatal allergic reaction to its horse serum basis. Although about 5 percent of untreated bite victims died from black widow bites in earlier times, black widow-induced fatalities are now unheard of.

RECLUSE SPIDERS. The brown recluse was not considered poisonous until 1957. In the ensuing four decades, it has become so well known that it is now often blamed as the cause of necrotic flesh wounds from states that have never supported populations of the spider and where verified finds are extremely rare.

The brown recluse is the most widely spread Loxosceles species in North America (southeastern Nebraska south to Texas, east to southwestern Ohio and Georgia). It is a common house spider in its endemic region and hence is a genuine health concern; its association with humans actually increases its populations. It is not uncommon to find hundreds of these potentially dangerous spiders living in one structure and it is difficult to eliminate them from households that have them. Despite the hyperbole surrounding them, brown recluses are rarely found outside their native range. Five additional Loxosceles species have significant distributions in the southwestern U.S. deserts. In contrast to the urban pest status of the brown recluse, the southwestern Loxosceles species appear to only be found in homes that are surrounded by native landscaping and are rare in typical urban homes.

Pinprick-like bites from recluse spiders occur most often when someone traps the spider against flesh. Despite the hyperbolic news coverage that ensues following a horrific recluse bite, it is almost never pointed out that brown recluse bites can vary from no reaction to a mild red wound to the terrifying rotting flesh wound. Ninety percent of all brown recluse bites heal without serious scarring. Current therapy is RICE (Rest, Ice, slight Compression, Elevation). Antiquated medical advice removed wound tissue but excision actually made the wound worse in many cases. It is rarely advised today, except in severe cases.

Despite the recluse’s reputation and the number of circumstantial deaths attributed to it, medical toxicologists who are recluse venom experts point out that there has not been one proven fatality due to a brown recluse in the United States. Although recluse spiders are relatively easy to identify by their pattern of six eyes, the public (and to a lesser extent, the medical community) is quick to misidentify any brown arachnid as a brown recluse, which reinforces the spider’s erroneous infamy.

The public (and the medical community) is convinced that brown recluses live throughout the U.S. and cause necrotic wounds everywhere. But, arachnologists and PCOs know that these spiders are not everywhere. This often causes confrontations between those who know spiders and those who think they know spiders.

HOBO SPIDERS. Since the late 1980s, the hobo spider, Tegenaria agrestis, has been implicated as a source of necrotic wounds in the Pacific Northwest (PNW). This European immigrant is currently found from British Columbia south into Oregon and east into Montana and northern Utah. They are reported to cause wounds similar to brown recluse bites and before hobo spiders were implicated, brown recluses were blamed for the wounds even though no recluses could be found in the PNW.

The hobo spider is a large, leggy spider that occasionally gets into homes where bites supposedly occur. However, on the PNW coast, the benign and similar-looking gigantic house spider, Tegenaria gigantea, is more common and confused as a hobo spider. Although it is now assumed that the hobo spider is poisonous, ongoing yet-to-be-published research is challenging this. A venom toxicologist was not able to experimentally duplicate the conclusions of the initial experiment implicating the hobo spider as the cause of necrosis in test animals. Therefore, the question of hobo toxicity may face an interesting reexamination in the next few years to determine its role in necrotic wounds.

YELLOW SAC SPIDERS. Yellow sac spiders (genus Cheiracanthium) also have been implicated as a health concern because they can supposedly leave mildly necrotic wounds, although often the only symptoms in verified bites are numbness and a tingling feeling. Bites from these spiders are painful at inception. Although there are two yellow sac spiders species in the United States, the most common species is a European native that is found coast to coast and is a common urban house spider.

INNOCENT SCAPEGOATS? Although research has made great strides along the lines of understanding the mechanism of medically important spider venoms and the treatment of their effects, spiders are often blamed for wounds they do not cause. The black widow is rarely involved in misdiagnoses because it is readily identifiable and the effects of its venom are diagnostic. However, because there are dozens of conditions that can cause mysterious skin eruptions, recluse, hobo and yellow sac spiders are often implicated as the causative agents of these afflictions.

In the last decade, I have been investigating both literature and incidences of medically important spider bites; my findings are that much of our assumed "knowledge" regarding spider bites is based on circumstantial evidence, poorly reported medical case histories and misdiagnoses of other conditions.

For example, in endemic recluse areas, about 10 percent of recluse bite victims bring to the doctor a recluse spider caught in the act of biting or from the vicinity of the envenomation locale.

I have heard of several hundred California "brown recluse bite" diagnoses, which is no doubt a fraction of those that are made. If these diagnoses were correct, then hundreds of brown recluses would be turned in to California doctors annually and PCOs should be able to find thousands. In reality, only one brown recluse is found every five years or so in the state and it is a single interception from interstate commerce. From conversations with arachnologists and PCOs from western, northern and eastern seaboard states outside the native range of the brown recluse, the same scenarios of misdiagnoses and erroneous public assuredness of the recluse’s presence occurs in their states as well.

From non-endemic recluse areas, "brown recluse bites" have turned out to be Lyme disease, infections of bacteria, fungus and virus, low-grade disease that can lead to fatal lymphomas, diabetic ulcers, skin conditions associated with underlying physiological diseases, poison ivy or oak, chemical burns, etc., as well as a multitude of blood-feeding arthropods (mites, ticks, bedbugs, kissing bugs, fleas). What also is starting to come to light is that verified spider bites result in wounds that are not caused by the spider’s venom but instead by bacteria or fungus inoculated during fang puncture, which may help to explain some of the paradox associated with hobo or yellow sac spiders or any spider that can pierce human skin. Physicians need to exert more scrutiny in their diagnoses because some of these misdiagnosed conditions can lead to irreversible damage or death.

In its native range, the brown recluse should be considered a health concern and a valid pest control issue. However, in non-native recluse areas, a public health dilemma exists for PCOs. Say a homeowner is diagnosed by a doctor as having a brown recluse bite. The "bite" victim requests insecticide treatment for brown recluses. The PCO knows that brown recluses do not live in the area and tries to educate the customer. The "bite" victim typically will believe the medical professional rather than the PCO who knows more about spiders than the doctor. The PCO is now faced with the prospect of refusing to spray unnecessarily or spray for non-existent spiders, which may not eliminate the actual cause of the victim’s "bites." At this point, the pest management professional could lose a contract due to assumed incompetence or worse, be sued for negligence.

CONCLUSION. Spiders are a legitimate health concern for some parts of the country. However, because of all the hyperbole, arachnophobia and sensationalistic "knowledge" surrounding spider bites, there are many untruths that need to be separated from reality; PCOs are often forced to deal with psychological aspects as well as arachnological ones to perform their vocation. The author is studying distribution of both recluse and hobo spiders and would like to receive specimens from PCOs who think they have either of these species, especially from northern California and Nevada. Send specimens to Rick Vetter, Entomology, University of California Riverside, Riverside, CA 92521. Please include collection information with specimens.

Editor’s note: In March PCT, Rick Vetter asked PCOs to send him brown recluse and hobo spiders for a research project. Do not send alcohol unless you follow the regulations for mailing flammable liquids. It may be better to preserve the spider in alcohol for a week and transfer it to a leakproof container filled with water the day of shipping (mark the package "package contains water.") Dead spiders can be sent also if carefully packaged, however, it will be more difficult to identify them when desiccated.

The author is a research associate at University of California, Riverside. He can be reached at rvetter@pctonline.com.