The bad news is that some spiders do bite people, and these bites can be dangerous. The good news is that spider bites are actually quite rare events. A recent summary of reported spider bites in the United States between 1989 and 1993 included fewer than 5,000 incidents per year. Only about 10% of other spider bites had serious consequences. These numbers seem small when compared to the over 800,000 dog bites that required stitches each year (source: Centers for Disease Control). During the study period, dog bites were responsible for 20 deaths per year, and auto-deer collisions were associated with 130 annual deaths. You might be surprised to learn that there were no spider-bite related fatalities during that four-year period.
Worried patients arrive at the hospital saying “I don’t know what bit me but it hurts so much it must have been a spider…” and unfortunately doctors are sometimes willing to accept this premise. In reality, many injuries that are reported as spider bites are actually caused by other small animals (fleas, lice, mosquitoes, biting flies, ant bites and stings, etc.). One national study of 600 cases of suspected spider bites established that roughly 80% were not actually caused by spiders. A particularly famous headline story involved a group of injuries associated with orchard workers in Florida. The workers’ sores were first thought to be the result of spider bites, but they turned out to be secondary infections following spine punctures from working on the trees.
The problem of misdiagnosis of spider bites is widespread. One reason is the rapid rise of skin infections caused by a particularly nasty form of antibiotic-resistant bacterium. This condition is called MRSA (short for Methicillin-resistant Staphylococcus aureus). This strain of bacteria is now widespread in many public places, particularly hospitals and gyms. The infections result in a spreading necrotic sore that superficially resembles severe reactions to the bites of brown recluse spiders. Combined with the widely held belief that recluse bites are common, it has caused misdiagnoses to spike. This is more than a PR problem for spiders; it is a serious medical problem. Misdiagnosis can lead to delayed or even inappropriate medical treatment. Misdiagnosis of MRSA infections can even lead to death. Until the true cause of a wound is discovered and treated, the patient suffers and the problem worsens. More information about the problem of misdiagnosis as spider bites is provided here.
Spider bites are most serious when the victim is very young or aged. Particularly sensitive persons of any age may also have an adverse reaction to animal bites. Many of us know someone who is very sensitive to bee or wasp stings. The bite of a normally harmless spider might be a serious problem for such a person. The venoms of spiders are the result of spiders’ adaptation to its predatory habits. The venom is generally most effective at killing their natural prey, usually an insect. Dangerous spider venoms usually act against the nervous system (neurotoxic) or the blood (hemotoxic), but humans are often unaffected by spider venom because of our large size and different physiology.