Heterodon nasicus

Geographic Range

The geographic range of western hognose snakes, Heterodon nasicus , extends from southern Canada to northern Mexico. Its range is bordered to the west by Colorado and Wyoming, and in the east by Illinois.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Heterodon nasicus is found at elevations of 90 to 2400 m. It is found in shortgrass prairie, dry rocky lands, and coastal islands (Johns, 2000). It prefers areas that are for the most part dry and sandy. According to Wright (1957, p. 299) H. nasicus is "Distinctly a prairie species, almost every writer refers it to sandy tracts such as sandy hills, sand dunes, sandy flood plains, sandy prairies, sandy areas, and sandy fine loam." The reason for its preference of sandy areas is that it is a snake that likes to burrow into the soil, mainly to search for food (Wright, 1957; Shaw and Camplbell, 1974).

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland

Physical Description

In comparison to other snakes, H. nasicus is small to medium in size, with an average length of about 50 centimeters, and a weight between 80 and 350 g. The dorsal side these snakes is grayish brown or a light olive green with approximately 40 dorsal spots that are a darker shade of olive green. ventrum is mainly white, but is black underneath the tail. The head is lighter in color than the body, but is strongly marked with dark brown bands across the top and behind the eyes. Each snake has 23 rows of dorsal scales. Perhaps the most distinguishing characteristic of H. nasicus is its upturned nose, which is uses for digging and burrowing.

Development

As soon as young western hognose snakes hatch they are fully developed, but just smaller in size at about 14 to 18 centimeters. Within hours the young are fully capable of actively searching out prey.

Reproduction

These snakes are described as polygamous. Females will breed with more than one male throughout the course of the breeding season to ensure fertilization, but apparently males also will breed with multiple females. When a female sheds her skin, a chemical is released. Males pick up this scent and actively search for the females. If the female is receptive upon discovery the two will copulate.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

The mating season for H. nasicus occurs between the months of June and August, as males actively seek out females to breed with. Females lay from 4 to 23 eggs between June and August. Once the eggs have been fertilized they are buried in the sand and hatch in 52 to 64 days.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
• oviparous oviparous

After having buried its eggs, H. nasicus invests no parental care into its young. This is why it is important that the young are fully developed upon hatching.

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning
  • protecting
    • female

Lifespan/Longevity

Heterodon nasicus has a life expectancy of around fourteen years in the wild. For the most part this is average in comparison to other snake species.

Behavior

Heterodon nasicus hibernates each year from September to March. It awakens in March at the beginning of the mating season. These snakes are solitary except for the duration of the mating season. They are also crepuscular, which means that they are most active in the early morning and in the late evening. When not active, these snakes attempt to find a burrow created by a small mammal to retreat into. Such a retreat helps them regulate their body temperature, as well as giving them a place to rest. As part of their thermorgulatory behavior, these snakes regularly move to areas that are either warmer or cooler to raise or lower body temperature.

Western hognose snakes have an impressive bluffing display when threatened. They rear back, flattening their heads, take deep breaths which inflate their size, and make very loud hissing sounds. They will strike at objects, but typically have their mouths closed. They are not known to bite, even in self defense. Heterodon nasicus will feign death when this bluffing behavior fails to ward off an enemy. In this case, the snake turns belly up. This behavior is apparently induced by parasympathetic arousal or adrenal medullary function.

• Key Behaviors
• terricolous
• fossorial fossorial
• crepuscular crepuscular
• hibernation hibernation
• solitary solitary

Home Range

The home range size of these snakes has not been reported. However, it is reported that they are not territorial, and that multiple adults will reside in the same area.

Communication and Perception

Heterodon nasicus is a species that lives a solitary lifestyle, and the only time that it needs to communicate with other members of its species is during mating season. This communication occurs when the male snakes pick up a chemical scent that the female produces as she sheds her skin, signaling that she is ready for a mate. Males will track the female by the scent.

Some communication occurs with other species. This communication involves visual signals, noises, and sometimes tactile cues. When western hognose snakes encounter a potential predator, they will at first hiss, and flatten their heads and necks to make themselves appear larger. If this fails to ward off the predator, the snake may strike--although it does not bite, apparently, this movement is threatening. If this fails, the snake will feign death in hopes that the predator will lose interest.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• infrared/heat infrared/heat
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Heterodon nasicus searchs for its prey, often by using its upturned nose to dig holes in the ground while looking for toads burrowed into the sand. Toads are the main food item of H. nasicus , and can make up nearly 80 percent of its diet in certain regions. When in the mouths of the snakes, toads will swell in order to make themselves too big to swallow. In order to counter this, H. nasicus has its bigger teeth in the back of its mouth, allowing these snakes to puncture the toads if they try to inflate. Another adaption on the snakes' part is an enlarged adrenal gland, which functions in negating the toxins found in the toads' skin. The enlarged adrenal gland can produce enough adrenalin to counteract the digitaloid (which slows down the predator's heart until the point of death) released by the toads as a means of denfense.

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates

• Animal Foods
• mammals
• amphibians
• reptiles
• eggs

Predation

Heterodon nasicus has two main anti-predator adaptations, both of whihc are behavioral. The first line of defense for this snake is to make itself appear larger by making its head and neck flatter. This flattening is accompanied by extremely loud hissing and blowing, whihc apparently makes the individual seem enraged and dangerous. If this defense fails to ward off a predator, the snake will shift into phase two of its defense. This begins with the snake spasming uncontrollably, and then rolling over on its back, lying motionless. Western hognose snakes will feign death in order to make a predator lose interest. When an indivudual perceives an absence of danger, it will resume its activities.

• Anti-predator Adaptations
• aposematic aposematic

Ecosystem Roles

Heterodon nasicus does play an important role in its ecosystem by keeping toad populations from exploding. It is one of the few species that has the ability to cope with the toads' poison, so it is possible that the removal of this species could in fact alter that particular ecosystem.

Economic Importance for Humans: Positive

Its mild temperament makes H. nasicus an ideal pet snake, because it is extremely docile and rarely bites. Once handled by humans enough, the snakes are calm and there is little or no danger of them biting. This snake has an extremely mild venom, and so does not pose a health risk to humans even if a human manages to get bitten.

In addition to their importance in the pet trade, these snakes help people by controlling toad populations. Without these snakes, the toad population could rise high enough so that the toads would infringe upon human establishments. Domestic animals eating toads might be harmed by their toxins (Allen, 1997).

• Positive Impacts
• pet trade pet trade
• controls pest population

Economic Importance for Humans: Negative

Western hognose snakes are docile and generally do not harm people.

Conservation Status

Heterodon nasicus is not given national status as endangered or threatened. However, because of habitat destruction, the numbers of H. nasicus have declined by a considerable amount in certain regions, and as a result western hognose snakes are listed as threatened or even endangered in some of the states in which they reside. These states include Iowa and Illinois. Numerous human developments have pushed western hognose snakes from their sandy habitat into more wooded areas, where it is ill-equipped for survival. In these states there are programs to help save these snakes' habitats. In the southern states, such as Texas and New Mexico, western hognose snakes are quite common. In these areas there is no shortage of the sandy areas which are optimal for these snakes, so they are able to thrive.

Other Comments

Various people have questioned whether or not this snake is actually venomous. However, an article published by Michael A. Morris describes the effects that the bite of H. nasicus had on him. He experienced swelling and tenderness of the bitten are for two days, and came to the conclusion that the snake does have venom with hemotoxic effects (Morris 1985).

Additional Links

Encyclopedia of Life

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Matthew Kerns (author), University of Michigan-Ann Arbor, Kerry Yurewicz (editor), University of Michigan-Ann Arbor.

References

Allen, S. 1997. "Western Hognose Snake" (On-line). Colorado Herpetologial Society. Accessed November 27, 2004 at http://www.coloherp.org/careshts/snakes/hognose.php .

Johns, N. 2000. "Western Hognose Snake" (On-line). Accessed March 22, 2002 at http://www.rw.ttu.edu/sp_accounts/hognose_snake/Default.htm .

LeClere, J. "Iowa Herpetology (Western Hognose Snake)" (On-line). Accessed March 21, 2002 at http://www.herpnet.net/Iowa-Herpetology/reptiles/snakes/western_hognose_snake.html .

Morris, M. 1985. Envenomation From the Bite of Heterodon Nasicus (Serpentes: Colubridae). Herpetologica , 41: 361-363.

Rolling Hills Zoo, 2001-2002. "Rolling Hills Refuge" (On-line). Western Hognose. Accessed March 21, 2002 at http://www.rhrwildlife.com/theanimals/h/hognosewestern/ .

Shaw, C., S. Campbell. 1974. Snakes of the American West . New York and Toronto: Alfred A. Knopf, Inc, and simultaneously by Random House of Canada Limited.

Wright, A., A. Wright. 1957. Handbook of Snakes . Ithaca, New York: Comstock Publishing Associates.

2000. "Western Hognose Snake" (On-line). Arizona-Sonora Desert Museum. Accessed November 27, 2004 at http://www.desertmuseum.org/books/hognose_snake.html .