elapids will remain attached and "chew'' on their victim to

inject the venom. Although this makes it more difficult fur

these snakes to deliver a clinically significant amount of

venom, it also makes it more difficult to clinically assess a

patient with a potential bite, as there may not be bite or fang

marks in a patient who has had a potentially life-threatening

envenomation.

..... Spiders

Like snakes, there are 2 major groups of spiders that cause

medically significant envenomations in North America: the

black widow (genus Latrodectus) and the brown recluse

(genus Loxosceles). It is difficult to estimate the true incidence of spider bites, because the history of a bite is often ­

times unreliable, with many patients and physicians

reasoning that a rash, abscess, or cellulitis originated from a

spider bite when no spider was seen. Additionally, with the

CHAPTER 65

Figure 65-2. North American cora l snake.

Reproduced with permission from Knoop K}/

Stock LB/ Storrow AB/ et of. The Atlas of

Emergency Medicine. 3rd ed. New York:

McGraw-Hill Medical/ 2009. Figure 1 6.30.

Photo contributor: Steven Holt MD.

possible exception of the female black widow spider, the

general public has difficulty distinguishing medically rele ­

vant spiders from those that are generally benign. That

being said, bites from brown recluse and black widow

spiders can be deadly in extreme circumstances and can

unquestionably cause substantial morbidity and pain.

There are 5 species of black widow spiders found in

the United States. These spiders are medium-sized, typically black colored, and have species-specific ventral

markings. The female Latrodectus mactans has the characteristic red hourglass ventral marking and has a larger

body and fangs than her male counterpart, making the

female more likely to cause envenomation (Figure 65-3 ).

The clinical effects of a black widow spider envenomation

in humans are thought to be caused by the neurotoxin

a-latrotoxin.

There are 2 major species of recluse spiders found in

the United States: the Loxosceles reclusa (brown recluse)

and Loxosceles deserta (desert recluse). The brown recluse

is found primarily in the southern and midwestern United

States, and the desert recluse's range is in the southwestern

portion of the country. North American recluse spiders

are brown to gray-colored with dark dorsal markings

that have a violin pattern, giving it its other names, fiddle ­

back or violin spider (Figure 65-4) . The toxin in recluse

spider bites is complex, but is thought to contain

proinflammatory and necrosis-inducing substances

similar to phospholipase D and hyaluronidase.

CLINICAL PRESENTATION

� Snakes

The severity of a crotaline envenomation depends on

multiple factors, including the amount of venom delivered, the potency of the venom, and the location of the

venom (anatomically and by depth), as well as clinical

Figure 65-3. Black widow spider,