Field Guide to Venomous and Medically Important Invertebrates ...

There are several commercially available widow spider antivenoms. These antivenoms include
those for the black widows (L. mactans, L. indistinctus) of North America (Merck), the red-back
spider (L. hasselti) in Australia, and brown widow (L. geometricus) spiders of South Africa, the
Argentinian L. mactans, and the Mexican widow spider. European widow spider (L.
tredecimguttatus) antivenom is no longer produced. Although these antivenoms produce few
allergic responses, and they have been shown effective under laboratory conditions in addition to
having cross-reactivity between many species, they are seldom used. Treatments for
envenomation by black widows may include use of antivenom for high-risk patients, but muscle
relaxants such as calcium gluconate, magnesium sulfate, and diazepam are more commonly used
treatments. Historically, an effective treatment included use of muscle relaxants and an
intravenous solution of 10% calcium gluconate. Recommendations for pain control include
intravenous morphine sulfate for severe cases and aspirin and acetaminophen for milder
envenomations.
Brown recluse spiders
Brown recluse spiders (Loxosceles spp.), also known as fiddlebacks, are widely distributed
throughout the world with over 100 described species in the genus. Envenomation by some of
these species has well documented dangerous effects on people. Not all of the known species
have been shown to be dangerous, but it is possible that many pose a potential health threat to
people. Antivenoms are available for Loxosceles spp., but there is little evidence to support their
effectiveness, particularly against local effects. The known and potentially dangerous species of
Loxosceles are shown in Appendix 1.