UGA researchers studying defensive behaviors of venomous snakes

Athens, Ga. – Researchers from the University of Georgia Savannah River Ecology Laboratory and Stetson University have studied the defensive behaviors of venomous snakes for years. A new report in the journal Copeia expands this work. Pygmy rattlesnakes, common in the Southeast, frequently bite humans who may equate their smaller scale with little danger. Xavier Glaudas put on his gloves – literally – to put these mighty mites to the test.

Habitat destruction and fragmentation combined with development of outdoor recreation has resulted in increased incidences between humans and animals, according to Glaudas. As venomous snakes are among the few species of animals that pose a direct threat to humans, many have received a reputation for aggression. Rattlesnakes especially are considered by the general public to be vicious.

“Snakes are responsible for approximately 30,000-40,000 human deaths worldwide per year,” said Glaudus.

Central Florida has a large population of pygmy rattlesnakes and this allowed Glaudas and fellow researchers Terence Farrell and Peter May from Stetson University in Florida to obtain a large sample size for their study – 336 individuals. They looked at many factors, including location, body size, sex, reproductive condition of mature females, initial posture and whether the snake had either recently eaten or shed its skin. The goal of the study was to determine if the pygmy rattler deserves its aggressive reputation.

Two to three times a week Glaudas, Farrell and May went snake-hunting in woodlands surrounded by a freshwater marsh in Volusia, Fla. Upon finding a snake, one of the team would approach the snake and gently tap it on the snout with a gloved hand. The snakes’ reactions were recorded: Did they flee, rattle or strike? Prior studies indicated that a human hand elicits high levels of what Glaudas called “antipredator behavior.”

“Most of the tested snakes did not react to our approach and test,” said Glaudas. “Of the 336 different snakes tested over the course of this study, 255, or almost 76 percent, did not strike or flee when threatened. They usually remained in the position where found and did not visibly respond to our stimuli.”

Another 54 (16.1 percent) snakes fled, 13 (3.9 percent) struck and fled and 14 (4.1 percent) struck and held their ground. Striking behavior appeared to be affected only by the initial posture of the snake: uncoiled snakes struck more often than those that were coiled (17 percent to 5 percent). Fleeing behavior was affected by sex and whether the snake was about to shed, as well as its initial posture. Females, those about to shed and uncoiled snakes were most likely to flee.

Glaudas said that based on this study he believes this species is not highly aggressive. Also, he believes his findings support previous studies that suggest that venom is primarily an offensive weapon used to subdue and predigest prey rather than a defensive weapon. “Presumably, the costs of defensive striking generally outweigh the benefits for venomous snakes,” he concluded.