An approach to spider bites. Erroneous attribution of dermonecrotic lesions to brown recluse or hobo spider bites in Canada.

OBJECTIVE To dispel prevalent myths surrounding diagnosis of dermonecrotic and associated conditions supposedly resulting from bites of brown recluse, hobo, or other spiders in Canada.

SOURCES OF INFORMATION Worldwide, spider bites are regularly misdiagnosed as the etiologic agents in human dermonecrosis mainly as a result of inaccurate, erroneous, or hyperbolic popular and professional literature based on inference, circumstantial evidence, inferior clinical trials, and misunderstanding of the facts regarding spider-bite envenomation.

MAIN MESSAGE A working diagnosis of "spider bite" or publishing a case history should be considered only when a spider is caught in the act of biting or otherwise reliably associated with a lesion. Accurate identification of the spider could be critical for correct diagnosis and subsequent treatment.

CONCLUSION Brown recluse spiders are not found in Canada. Hobo spiders have not been reliably implicated in dermonecrosis. Worldwide, spider-bite envenomation is an unlikely cause of dermonecrosis. Canadian physicians should give priority consideration to other, more likely, causes.