Department of Earth and Biological Sciences
Faculty: William K. Hayes
Laboratory of behavioral ecology and conservation
Shelton S. Herbert (PhD, in progress)
"Factors influencing venom expenditure during defensive bites by viperid and elapid snakes."
Shelton S. Herbert (MS, 1998)
"Factors influencing venom expenditure during defensive bites by cottonmouths (Agkistrodon piscivorus) and rattlesnakes (Crotalus viridis, Crotalus atrox)."
Contact
Department of Earth and Biological Sciences
Loma Linda University
Loma Linda, CA 92350 USA
Phone: (909) 558-4300, extension 48909 or 558-4530
Fax: (909) 558-0259
Email: sheltonherbert@netscape.net
"Scott" with research subject. This Northern Pacific Rattlesnake (Crotalus oreganus) was a cheerful contributor to Scott's master's thesis research. Photograph: William K. Hayes.
Scott completed his Master's degree in my lab and decided to stick around for more misery. His M.S. thesis examined factors influencing venom expenditure during defensive bites by rattlesnakes and cottonmouths. You can read a summary of his findings below. He has continued along a similar line of inquiry for his Ph.D. work. However, he has expanded the coverage of study to include other viperid species and cobras, working with Jim Harrison at the Kentucky Reptile Zoo. Among his more interesting findings, his data suggest that rattlesnakes inject approximately two-thirds less venom when striking a human limb protected by blue jeans (denim). Pretty cool, huh? It makes me think twice about wearing shorts when entering rattlesnake habitat...
We all appreciate Scott for some of his other hobbies and interests. We depend on his technological expertise to keep the lab computers up and running. He also helps others find the best electronics purchases, stocks the lab with snacks and drinks, and enjoys photography and target shooting. Several local colleges appreciate the contract teaching he regularly takes on. To learn more about his studies, go to Research on Venom Expenditure and Strike Behavior of Snakes.
MS thesis abstract
Although the quantity of venom expended when biting is an important aspect of the natural history of snakes, little is known regarding the quantities of venom expended during bites. Recent studies have shown that rattlesnakes appear capable of selectively allocating their venom reserves during predatory strikes, metering more venom into certain prey types and less into others. Despite much speculation, the quantities of venom expended during defensive bites are poorly understood. The purpose of this study was to examine the factors that influence venom expenditure during defensive bites by cottonmouths (Agkistrodon piscivorus), western rattlesnakes (Crotalus viridis) and western diamondbacks (C. atrox). Defensive bites were elicited by models of human limbs (warm saline-filled gloves) and by voluntary venom extractions into a parafilm-covered beaker. Biting behavior of the snakes was analyzed via slow-motion videotape review. The mass of venom expended by snakes was measured by protein assay.
The amount of venom expended during defensive bites was positively correlated with snout-vent length of the snake. Agkistrodon piscivorus and C. viridis expended similar quantities of venom in the laboratory, but C. atrox tested under less-controlled field conditions expended somewhat less venom. Different body temperatures had no discernable effect on biting or venom delivery. Venom expenditure was also proportional to the duration of fang contact during the bite. Consequently, bites of brief duration may constrain delivery of venom during a bite and therefore contribute to the occasional occurrence of ‘dry bites’ in human snakebite victims. Quantities of venom expended in the laboratory studies were substantially greater than amounts reported previously for predatory bites of mice. Because the duration of fang contact was similar for defensive and predatory bites, it appears that snakes have the intrinsic ability to meter their venom, allocating more during defensive bites and less during predatory bites.
Herbert, Shelton S. 1998. Factors influencing venom expenditure during defensive bites by cottonmouths (Agkistrodon piscivorus) and rattlesnakes (Crotalus viridis, Crotalus atrox). Unpubl. MS Thesis, Loma Linda University, Loma Linda, California. vi + 59 pp.