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 parafilmcovered 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.

LLU Discipline





Graduate School

First Advisor

William K. Hayes

Second Advisor

Ronald L. Carter

Third Advisor

David L. Cowles

Degree Name

Master of Science (MS)

Degree Level


Year Degree Awarded


Date (Title Page)




Library of Congress/MESH Subject Headings

Snake Bites; Snake Venoms; Agkistrodon; Crotalus.



Page Count

vi; 59

Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


Loma Linda University Electronic Theses and Dissertations

Collection Website



Loma Linda University. Del E. Webb Memorial Library. University Archives

Included in

Biology Commons