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Approach to the patient with a suspected spider bite: An overview

Richard S Vetter, MS
David L Swanson, MD
Section Editors
Daniel F Danzl, MD
Stephen J Traub, MD
Deputy Editor
James F Wiley, II, MD, MPH


Spider bites are rare medical events. Of the thousands of spider species that exist around the world, only a handful causes problems in humans [1]. There are a variety of more common disorders that can mimic a spider bite, some of which represent a far greater threat to the patient if not recognized and treated appropriately.

Thus, accurate diagnosis is the initial goal of the clinician evaluating a patient with a lesion that might represent a spider bite. Discerning among the various conditions in the differential diagnosis of a spider bite requires familiarity with these disorders, as well as a basic understanding of the distribution and behavior of medically important spiders.

The spiders of medical importance, an overview of the clinical manifestations of their bites, and diagnosis and differential diagnosis of spider bites will be reviewed here. The assessment and management of spider bites caused by recluse and widow spiders are discussed separately. (See "Bites of recluse spiders" and "Clinical manifestations and diagnosis of widow spider bites", section on 'Clinical manifestations' and "Management of widow spider bites".)


Spiders are arachnids (a group of arthropods), which have four pairs of legs, similar to scorpions, mites, and ticks (figure 1). They use sharp fangs at the end of their chelicerae to bite prey (typically insects, other arthropods, or small vertebrates) and inject venom.

Most spiders pose no threat to humans. The venom of most spiders has little or no effect on mammalian tissues [2,3]. In addition, only a few species have cheliceral muscles powerful enough to penetrate human skin, and most of these spiders bite humans only in rare and extreme circumstances (eg, as they are being fatally crushed between skin and some object).

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Literature review current through: Nov 2017. | This topic last updated: Jul 12, 2016.
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