It would be hard to design a better rodent-killing tool than Mother Nature accomplished with the snake.
Dozens of species – from timber rattlesnakes (Crotalus horridus) who ambush squirrels and chipmunks, to mole snakes (Pseudaspis cana) who hunt voles in their burrows – sustain themselves by eating rodents and other small mammals.
But while snakes are rightly renowned for the pest-control services they provide, this reputation does them a disservice.
Rats and mice aren’t the only critters on their menus.
Snakes are a cosmopolitan group, and the diversity found across this nearly-3,000-species-strong clade is truly remarkable. Some snakes are large, some are small; some snakes live underground, others in the trees. Some snakes have legs (wait, what?), yet most do not. Some snakes kill their prey with venom; others use brawn.
Their diets exhibit similar diversity.
Rodents are certainly prominent in the diets of many snake species, but they are completely absent from the diets of others.
Gray-banded kingsnakes (Lampropeltis alterna) primarily hunt lizards, while Santa Catalina Island rattlesnakes (Crotalus catalinensis) feed almost exclusively on birds. Eastern hognose snakes (Heterodon platirhinos) are frog and toad specialists, while diamondback water snakes (Nerodia rhombifer) are piscivores with a predilection for catfish. Other species, such as the infamous king cobra (Ophiophagus hannah) of South Asia, subsist almost entirely on other snakes.
These types of things – rodents, lizards, birds, frogs, fish and snakes – probably make up the vast majority of the diets of the vast majority of snake species. They are the bread and butter of the “average serpent,” were such a thing to exist.
But what about those snakes who stray from the mean? What other species show up in the diets of snakes?
As it turns out, pretty much all of them.
Take insects, for example.
Insects are not commonly thought of as snake prey, yet racers (Coluber spp.) and copperheads (Agkistrodon contortrix) consume roaches, caterpillars and beetles when the opportunity arises. Researchers have also found bits of exoskeleton in the scat of green tree pythons (Morelia viridis).
However, these particular examples reflect the generalist nature of these species (particularly the racers and copperheads – green tree pythons primarily feed upon reptiles and rodents). They eat bugs during chance encounters, when other prey is unavailable or during periodic plenties. They grow large enough to consume typical snake prey and they make their living doing so.
But many species are much too small to consume mice or frogs. These snakes feed on insects and other invertebrates out of necessity.
Blind snakes of the families Typhlopidae and Leptotyphlopidae, for example, are some of the smallest snakes in the world. Six-inches-long and sightless, blind snakes primarily consume ants and termites, but they will eat just about any tiny arthropods they encounter.
Insects are not, however, the only invertebrates to appear in the diets of some snakes. Several small, terrestrial species consume earthworms, but ringneck snakes (Diadophis punctatus), garter snakes (Thamnophis spp.) and – wait for it – worm snakes (Carphophis amoenus) are particularly fond of them. Sticking with the soft and slimy theme, a handful of other snake species find slugs to be perfectly palatable. Some consume slugs opportunistically, but red-bellied snakes (Storeria occipitomaculata) deliberately seek them out.
While worms, slugs and caterpillars are relatively defenseless prey, for whom detection by a predator typically spells their doom, snakes have shown that even the most well armored animals on the planet can wind up looking down the business end of a hungry serpent.
Many animals rely on shells to protect themselves from predators, but no shell is perfect.
Snails are better protected than their slug cousins are, but they still appear on the menu of several snakes. These snail-eating specialists prowl the tropical forests of Asia and South America, using their specialized jaws to extract snails from their shells. In fact, an interesting arms race is currently taking place in these forests: The snakes have jaws that have evolved to extract snails whose shells coil in a clockwise direction. However, through a genetic mutation, some snails produce shells that coil in a counterclockwise direction, which renders them immune to the attacks of these snakes.
It doesn’t stop with snails — snakes have derived methods for eating all sorts of protected prey. Not even turtles are completely safe from snakes.
Anacondas (Eunectes sp.) and water snakes (Nerodia spp.) feed on aquatic terrapins, while indigo snakes (Drymarchon couperi), coachwhips (Masticophis flagellum) and racers feed on terrestrial turtles. Eastern kingsnakes (Lampropeltis getula) take it a step farther, and eat small turtles and their eggs (sometimes, particularly fresh eggs).
African snakes of the genus Dasypeltis, subsist almost entirely on bird eggs, while scarlet snakes (Cemophora coccinea) spend their lives searching for lizard eggs.
Of course, other snake species have an entirely different problem. Rather than having to devise methods for consuming shelled prey, they must devise methods for capture large prey.
Very large prey.
Snakes are gape-limited predators. Incapable of ripping, tearing or chewing their prey, they can only ingest prey small enough to be swallowed whole. Fortunately, snakes feature remarkable jaws, which allow them to swallow prey larger than their own heads.
It bears mentioning that snakes do not, as the animal-oriented infotainment cable networks would have you believe, dislocate their jaws. Instead, their jaws are constructed differently from those of most other vertebrates.
To oversimplify it: Typical vertebrate jaws feature and upper jaw, lower jaw and a single articulation point. By contrast, snakes jaws are comprised of an upper jaw, a lower jaw and a bone called the quadrate separating the two. This means that snakes posses two joints in their jaws, rather than the single joint you, dogs, cats and rhinoceroses possess.
Here, let herpetologist, snake-educator extraordinaire and author of my favorite book about snakes, Harry Greene explain:
(Aside: I performed thousands of educational presentations like this during my time as an environmental educator, and I frequently included a similar bit about snake jaws. I mean really similar – darn near verbatim. The arm-jaw analogy is an old bit that lots of educators use, but I thought I was the only one doing the cheeseburger bit. This is particularly strange, as I don’t like burgers at all – they’re just a good example for kids.
Nevertheless, I have been doing that routine since the late nineties, yet I only saw this video about 20 minutes ago.
Now, let’s be clear about the implications of this: Harry Greene has forgotten more about both snakes and teaching than I will ever know, and he has never even heard my name. Accordingly, it is simply impossible that he stole the cheeseburger routine from me. Therefore, the only conclusion we can possibly draw from this is that I stole it from him. From the future.)
The end result is that many snakes regularly consume food representing one-half of their body weight or more. There are even a small number of documented cases in which snakes have consumed prey with greater mass than their own. Such feats of consumption are nothing less than spectacular, and they become especially impressive when you consider what this means for the biggest species.
Green anacondas (Eunectes murinus) – the world’s largest snakes – find capybaras (Hydrochoerus hydrochaeris) – the world’s largest rodents – to be the perfectly sized for snacking. Bear in mind that capybaras are ridiculously large animals by rodent standards; big individuals often weigh more than 130 pounds.
A variety of other large animals, including deer, pigs, gazelles and other hefty mammals are commonly consumed by reticulated pythons (Python reticulatus), African rock pythons (Python sebae), Indian rock pythons (Python molurus) and other large constrictors. However, hooved prey is not solely the domain of boas, pythons and their kin; Gaboon vipers (Bitis gabonica), who usually measure less than 6 feet in length, prey upon royal antelopes (Neotragus pygmaeus).
Mammals aren’t the only large animals that find themselves looking up at snakes on the food chain. Even crocodilians – formidable, armored animals who sit brazenly atop most food chains – are often consumed by large constrictors.
The tendency for large snakes to eat large prey can be particularly problematic when a species expands its range. For example, Burmese pythons (Python bivittatus) have colonized portions of southern Florida, and they have been recording eating an array of large animals, including white-tailed deer (Odocoileus virginianus) and American alligators (Alligator mississippiensis).
Do any snake species eat bats?
Yup. Most rodent-eating snakes with climbing skills probably catch the occasional bat, but Puerto Rican boas (Epicrates inornatus) are particularly adept at snagging them in midflight.
What about frog eggs?
Giant aquatic salamanders?
In fact, turtle-headed sea snakes (Emydocephalus annulatus) subsist entirely on fish eggs. This specialized diet has even manifested in a drastic reduction of the species’ venom apparatus – their fangs have shrunk to about 1 millimeter in length, making it very difficult for them to inject venom effectively.
What about crayfish?
Why else would glossy crayfish snakes (Regina rigida) have chisel-shaped teeth? For that matter, why do you think they are called glossy crayfish snakes?
Alright smart ass, what about freshly molted crayfish?
Yes, some snakes eat monkeys.
What about, uh, bigger primates? Especially fur-less primates with opposable thumbs and language?
Yes. While it is undoubtedly rare, large snakes have consumed larger primates (including humans and our recent ancestors) from time to time throughout the thousands of years the two have lived alongside each other.
I could continue listing one obscure prey item after another, but you get the point. As a group, snakes eat just about everything.
These myriad examples not only help to correct the perception that snakes are little more than nature’s rodent control, but they also help demonstrate the dietary diversity of the group. This diversity isn’t only represented by the varied diets of different species. Some snakes are incredible generalists, for whom, dietary flexibility is the name of the game.
We touched on generalists earlier, sighting copperheads and racers as examples. But we’ll conclude today with one of the world’s grandest generalists (and one of my favorite species): the cottonmouth (Agkistrodon piscivorous).
Big, bold, baddies of backwater swamps and streams, cottonmouths eat what they want. Fish, frogs, snakes, rats, ducks and baby gators are all fair game, but like most generalists, they are great at exploiting whatever is abundant in their particular location.
The cottonmouths of Florida’s Seahorse Key have capitalized on just such a food source.
Seahorse Key is a popular nesting spot for many sea birds. They fly in and build nests in the island’s trees, where they lay eggs and raise young. To feed their offspring, the adult sea birds capture and swallow fish, before flying back to their nests. Once there, the adults regurgitate the now-vomit-covered fish, upon which the chicks feed.
Occasionally one of these vomit-covered fish falls to the ground.
Enter the cottonmouth.
These cottonmouths, who must have the most unrefined palates on the planet, often feed upon the dropped fish. In fact, this food source is so reliable that cottonmouths on the key regularly patrol the areas under the nests, specifically seeking out vomit-covered fish. At times, they even consume vomit-covered sticks, mistaking them for their more usual prey.
The idea that snakes primarily eat mice and rats probably reflects the efforts of environmental educators seeking to dissolve irrational fears about snakes, and highlight the roles snakes play in wild ecosystems. While these are worthy goals, the “snakes eat rodents” mantra fails to recognize the diversity of snakes and the array of roles they play in natural habitats.
So celebrate the rodent-eating abilities of snakes, but also celebrate the predatory pressure they apply to fish, frogs, bugs, worms, monkeys, birds, bats, snails, goats and eggs, as well.