Snake Food

Great Basin Gophersnake consumes baby bird

Bryan Hamilton

Snake Food
Have you ever wondered what snakes eat? Many people recognize that snakes are important controls on rodent populations but you may be surprised to learn how feeding strategies can vary between snake species. Food habits are an important component of a species’ ecology. Predators like snakes always occur in lesser numbers than their prey. For example the Utah Mountain Kingsnake, may feed primarily on relatively uncommon Western Skinks (Eumeces skiltonianus). This means that kingsnakes will be even less common than their already uncommon prey. The birth of many snake species occurs in synchrony with the birth and increased populations of their prey. Rattlesnake reproduction in the Great Basin is closely correlated with pinyon pine nut production. Two years following pine nut masts, rattlesnake reproduction peaks. Prey may also limit the distribution of their predators. Long-nosed snakes feed primarily on Great Basin Whiptails (Cnemidophorus tigris) and will not be found in habitats that do not also support whiptails.

There are many ways to learn what types of food an animal eats. Direct observation is simplest but because snakes are so secretive it is also the most difficult. As secretive predators feeding near the trophic peak of the food web, observing a snake feeding in the wild is a relatively rare occurrence. Count yourself as fortunate if you have observed a snake feeding in the wild. After feeding, snakes change their behavior. They seek warmer temperatures and tend to bask in the open more frequently. Often a snake that has recently fed will be tucked back into a hiding place with only a lump (the recently consumed prey) exposed to the sunlight. This often makes them easier to find and more vulnerable to predators themselves. Herpetologists can sometime induce a snake to regurgitate their fresh meal and then identify the meal. The most important way that herpetologists have studied the feeding ecology of snakes is through the dissection of preserved snake specimens. Many museums have large collections of snakes available for examination. The Monte L. Bean Museum of Life Sciences, Brigham Young University alone houses over 30,000 reptile and amphibian specimens. Such collections allow a large sample of snakes to be dissected. Even with these large samples relatively few food items are found. Snakes do not feed regularly and only about 10% of specimens examined contain food items. Through careful dissection and examination of stomach remains and fecal contents, a picture of the feeding ecology of a species emerges. Our understanding of snake feeding ecology is primarily based on studies of preserved specimens housed in universities such as BYU.

• The most common snake in the Great Basin is the Western Rattlesnake (Crotalus oreganus lutosus). Rattlesnakes are venomous, ambush predators. They typically set up in ambush along a rodent trail, with a characteristic S-shape in its neck. When a rodent approaches, the snake strikes, injects venom and releases the prey item. A few minutes later the snakes tongue flicking rate increases and it tracks the mouse’s trail via its sense of smell. Upon finding the now dead rodent the snake swallows it head first. The venom has two major advantages. It allows the snake to minimize contact with the potentially dangerous food item and begins digestion from the inside out. Great Basin Rattlesnakes undergo an ontogenetic change in food preferences as they mature from neonate to adult. Young rattlesnakes feed primarily on lizards (and small mice) while adults feed primarily on rodents (mice, woodrats, and chipmunks).
  
• Another common Great Basin snake is the Great Basin Gophersnake (Pituophis catenifer deserticola). Gophersnakes are known locally as “blowsnake” for the characteristic noise they make when disturbed. Gophersnakes feed on a wide variety of prey, but are notorious nest raiders, invading underground rodent nests and arboreal tree nests and feeding on the young nestlings. They will also feed on larger birds and rodents which they kill by constriction.
  
• Striped Whipsnakes (Masticophis taeniatus), known locally as “racers”, feed primarily on diurnal lizards. They are active foragers with binocular vision and they use their quickness to catch lizards. Whipsnakes also consume rodents and snakes, with several documented cases of cannibalism.
  
• Wandering Gartersnakes (Thamnophis elegans) are known locally as “watersnake” for their preferred habitat, springs, streams, and wetlands. Gartersnakes often feed on fish, amphibians, and small invertebrates such as worms, with larger individuals occasionally feeding on mice and birds.
  
• The Long-nosed Snake (Rhinocheilus lecontei) is a true feeding specialist. Approximately half of its diet is comprised of whiptail lizards, with reptile eggs and small mammals making up the remainder of its diet.
  
• Nightsnakes (Hypsiglena torquata) feed almost exclusively on small lizards (sagebrush and side-blotched lizards) and reptile eggs. Nightsnakes are venomous to their prey but are harmless to humans as they are unable to inject venom into humans.
  
• The distribution of the Racers (Coluber constrictor) in the vicinity of Great Basin National Park is limited to northern Spring Valley. Contrary to its scientific name racers are not constrictors. Racers are opportunistic predators and feed on insects (crickets), snakes, lizards, and rodents.
  
• Utah Mountain Kingsnakes (Lampropeltis pyromelana infralabialis) are infrequently encountered in the Great Basin. They feed on lizards and rodents, and less frequently on small snakes.
  
• The Ringneck Snake (Diadophis punctatus) is the rarest snake in the Great Basin. Because of the lack of records of this species its food habits in the Great Basin are unknown. In other western portions of its range, ringnecks feed primarily on lizards and are mildly venomous, but like the nightsnake, harmless to humans.

The feeding habits of many snake species vary widely geographically. For example racers in Virginia feed primarily on snakes while racers in the Great Basin feed primarily on crickets. Little data has been presented on the feeding ecology of snakes in the Great Basin. To address this data gap, Resource Management biologists are actively examining the feeding ecology of snakes in the Great Basin in cooperation with the Monte L. Bean Museum of Life Sciences and BYU.

The food habits of snakes are an interesting and important component of the overall ecology of the Great Basin. I can count on two hands the number of times I have observed a snake in the wild feeding. Count yourself as fortunate if you have observed this rare and spectacular event in the natural world.

Written in 2005 by Bryan Hamilton, Great Basin National Park.