by Greg Mayer
When Jerry posted about an olive python in Australia eating a wallaby, I appended some notes on snake feeding and pythons as pets. I concluded my comments by recommending two books for further reading on snakes, Harry Greene’s Snakes: The Evolution of Mystery in Nature, and Carl Ernst & George Zug’s Snakes in Question. While both are indeed very good, I noticed as I added the references that both were now over 15 years old, and wondered if perhaps I had missed some more recent contribution in the area of overviews of snake biology for a general audience. Well, it turns out I had, Harvey Lillywhite‘s new (2014) How Snakes Work from Oxford University Press. I got hold of a copy yesterday and have begun reading, and can recommend it as an addition to your snake reading list.
The book is written for a non-specialist audience, and is well illustrated with color and black & white photos, and line drawings. It is especially strong on physiological aspects of snake biology, and examples and photos are frequently drawn from the author’s own extensive work on snakes, so there’s a lot on marine snakes and Florida cottonmouths (Agkistrodon piscivorus conanti). (The author is a professor of biology at the University of Florida.)
The book provides some interesting further information about two issues I mentioned in my comments: how long does it take to digest prey, and how often do snakes need to eat. With regard to digestion, Lillywhite notes that in pythons digestion, or physiological processes related to it, can go on for 8-20 days. As I also stressed, rates vary considerably depending on temperature. He also notes that some snakes retain feces in the lower gut considerably after digestion is completed, recording a Gaboon adder (Bitis gabonica) that went 420 days between defecations!
As regards how often snakes need to eat, Lillywhite reports that even small snakes can go for long times between feedings, and that from considerations of energy balance a temperate zone garter snake can get by on one decent frog a year. This, of course, would not be something the snake would ordinarily do, since such a diet does not allow for growth, or, most important evolutionarily, reproduction. He notes that some rattlesnakes (which are not really big snakes) can survive up to two years without eating.
The most fascinating tidbit for me was his mention of carrion feeding in snakes. Snakes (and most lizards) are noted for the fact that they eat only live prey– a lizard will starve if surrounded by fresh, dead insects, and captive snakes can be difficult to teach to eat things like dead mice. Carrion feeding has been known in some snakes for awhile, but I’ve never seen it, and had never seen a picture of it till in this book. Here’s one of the Florida cottonmouths he studies eating a rather dead fish.
Carrion feeding seems to be important in the insular populations studied by Lillywhite, where the snakes gather under bird rookeries which have numerous dead and dying fish (dropped or regurgitated by the birds) underneath them.
Ernst, C.H. & G.R. Zug. 1996. Snakes in Question. Smithsonian Institution Press, Washington, DC.
Greene, H.W. 1997. Snakes: The Evolution of Mystery in Nature. University of California Press, Berkeley.
Lillywhite, H.B. 2014. How Snakes Work. Oxford University Press, Oxford.