Spider Fears, Spider Bite Diagnoses
(or Misdiagnoses)*, and
the Hobo Spider Controversy:
Are hobo spiders as dangerous as we think they are?
Spiders generally carry a severely negative connotation with most people, whether that is general unease, dislike, fear of its bite, or extreme arachnophobia. Our opinion of spiders has a very interesting, variable, and multi-faceted history. While many cultures (past and present) see spiders as symbols of good luck or mischief, a more modern (or Western) view of spiders tends to vilify them. This tendency may have stemmed from the Middle Ages, when spiders were often accused of causing illness, including the Great Plagues (Davey 17).
Many people dislike spiders because they are venomous creatures. While nearly all spider bites are benign to humans, either having no effect or minor effect (like swelling or itching), there are some spider species of medical concern. The most notable species of concern in North America are black widows (spiders from the genus Latrodectus) and the brown recluse, Loxosceles reclusa. There are about four species of Latrodectus spiders in North America, but the only species found in Idaho is the western black widow, Latrodectus hesperus. Female black widows are the conpsicuous larger ones with the very identifiable red hourglass; they are the spiders of medical significance (the male's venom is not as dangerous). Brown recluses are not found in Idaho, only the southeastern United States.
Arch Baker. Female brown recluse. Photograph. n.d. Loxosceles reclusa (Brown Recluse). Spiders.us. Web. 4 April 2014.
Davefoc. Male western black widow. Photograph. 2008. Lactrodectus hesperus. Wikipedia. Web. 4 April 2014.
Random fact: Western black widows exhibit sexual dimorphism. The genders differ in size and coloration.
The medical literature for bites attributed to certain spiders—including the hobo spider—is frankly quite inadequate when examined more closely. Many necrotic lesions that appear on the skin are attributed to spider bites, often off of presumption and biases resulting from the poor clinical reports. This becomes particularly problematic when the method of diagnosis of the spider bite is considered. Many of the spider bites were diagnosed without any definitive evidence of a spider biting the patient (Sun 3).
Misdiagnosis (wrongful diagnosis implicating a spider) is particularly dangerous because it would lead to improper treatment of a more serious underlying condition. Necrotic skin lesions are produced by a plethora of other conditions including (but not limited to) bacteria or fungal infections such as MRSA (Methicillin-resistant Staphylococcus aureus), basal cell carcinoma, or anthrax (Vetter & Isbister 607).
Darwin Vest's initial research implicating the hobo spider as a cause of necrotic skin lesions is of interest because it was not definitive evidence, yet the medical community and the public still ran with it. My research (so far) is leading to the probable conclusion that hobo spiders are not medically significant spiders.
A notable fact is that hobo spiders are endemic to western Europe. They are seen as medically significant spiders in North America but not in its native Europe when there has been no change in their venom components between the endemic and nonendemic populations (Vetter & Isbister 606).
The only known verified hobo spider bite that has caused a necrotic skin lesion was in a woman with a history of phlebitis (this disease commonly causes ulcerations) (Vetter & Isbister 606). "It is thus not clear what role the spider played; it may have just exacerbated her previously existing condition" (Sun 5).
Hobo spider bites have often been seen to be implicated circumstantially (consistent with many spider bite diagnoses). In a study by Darwin Vest, twenty-two cases of suspsected "necrotic arachnidism" implicated hobo spiders just because the said spiders were found in the homes of sixteen out of twenty two patients (Vetter & Isbister 605). Out of these twenty-two cases, only four had a confirmed bite (a spider was seen biting the patient) and none of them had the spider submitted for identification by an expert arachnologist. A spider bite cannot be verified unless the spider is seen biting the patient, captured, then sent to an expert arachnologist for correct identification.
So far, when closely examined, the evidence that hobo spiders are medically significant is rather sketchy. However, there needs to be much more comprehensive research done to come to definitive conclusions.
If you want a more thorough explanation of this probable false implication of hobo spiders, it can be found in my Unit 1 piece:
*This page is not meant to substitute for medical advice or diagnosis. If you have a spider bite or some other symptom(s), please talk to your medical practitioner. While most spider bites are benign, there can be rare, but legitimately serious cases. If you have been bitten by a spider, try to catch the spider so it can identified by an expert arachnologist.