Several times each year someone asks in class about the relative danger of an envenomation from a small versus a large crotaline (aka pit viper). Some people are insistent that smaller snakes are more dangerous. This idea has always felt counterintuitive to me. The explanations seem fanciful at best. Usually, people argue that larger (and therefore older) snakes possess some sort of volume control. They argue that larger snakes hold back venom against humans because we are not food for them. These larger snakes want to warn us with a strike but preserve venom for when it matters, like a meal. I have been unable to find any science and none of the experts that I have spoken with can give a definitive answer one way or the other. With the publication of a recent study, perhaps this theory will disappear.
This past December the Annals of Emergency Medicine published an article by Herbert and Hayes (2009; Volume 54 #6: p 831) in which they argue that a protective layer of denim over the skin may help to decrease the severity of an envenomation from a defensive strike by a southern Pacific rattlesnake. (I leave you to view the details and decide for yourselves.) In their study, after provoking a test snake, they presented it a latex glove filled with warm water, one time bare and another time covered with a denim glove. After a bite, they measured the venom in the water within the latex glove and, when used, on the denim glove. The order of the trials were randomized and occurred 2 weeks apart. They found that the amounts of venom measured were consistently and significantly greater from the larger (greater than 66 cm in length) versus the smaller (less than 55cm) snakes.
In the discussion section, they point out the volume differences as well as information from other sources that argue against the smaller is more dangerous theory. Included are the facts that larger snakes are more likely to strike and that their strikes are more accurate. Large snakes have longer fangs with larger hollow spaces allowing for deeper penetration and more venom flow. They cite references (that I did not check) that claim that larger snakes cause more serious envenomations. Herbert and Hayes state:
Thus, the more effective antipredator deterrent of bites from larger snakes may explain why they resort to biting more readily than smaller snakes.
And maybe Homo sapiens don’t learn to stand back.
Although the results from this study do not definitively answer the question about size it does lend some scientific basis for debunking an unfounded belief. Practically, of course, it does not really matter. The anticipated problem of a venomous snake bite is an envenomation. There is no good way to predict beforehand who will be envenomated, and if so, how bad it will be. We treat what we see. By the way, some skin covering, like denim, seems better than none.
In my own testing using live mice, I found that drop per drop younger snakes venom is more potent. That is why the larger snakes inject more. Using equal amounts of crotalus adamanteus venom that death was substantially quicker using venom from younger specimens. My hypothesis is with every meal, the animal grows larger and produces more venom to fill the void, but, it is dilluted in potency.
Has anyone ever published such findings?? Or should I repeat my tests for publication??
In general, adult venomous snakes, with their longer fangs and larger amounts of venom to inject are going to deliver more dangerous bites than their young. There have been studies [I know of one involving Crotalus atrox] that have suggested that neonates may have slightly more potent venom, mg for mg. Some young pit vipers begin life feeding on reptile and amphibian prey, and have neurotoxic components in their venom, which becomes more haemotoxic as the snake matures to prey upon homeothermic animals. It has been determined, however, that some 20% of snakebites to humans are “dry” bites, thus suggesting that snakes do selectively inject venom. For people who work with venomous snakes, I would say that the primary reason smaller snakes can be more dangerous is that they are often seriously underestimated. In some 40 years of working with snakes, I can say that young snakes are often much more defensive, nervous and quicker to strike than adults. Ultimately though, if it had to happen, I’d rather take a nip from a neonate eastern diamondback than a large adult!