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Heterodon

By Sarah Shassetz

Diversity

There are multiple species within the genus Heterodon. Heterodon platirhinos commonly known as eastern hognose snake, named for its geographic location. Heterodon nasicus commonly known as the western or plains hognose snake. Heterodon kennerlyi commonly known as the Mexican hognose snake with the specific epithet a patronym to Carl Kennerly who was a surgeon and expeditionist in North America and Mexico. Heterodon simus otherwise known as the southern hognose after its distribution throughout the southern United States. Hognose snakes are different from other snake taxa because of morphology and how they deter predators by playing dead. All species of Heterodon have upturned snouts and stout bodies that allow for to burrow in dirt and leaf litter. (Kroll, 1976; Kroll, 1997; Rouse, et al., 2011; Uetz, et al., 2019a)

Geographic Range

All species in the genus Heterodon are found throughout North America from Canada through Mexico. Heterodon platirhinos is located in southeast Canada and the southeastern United States (Florida, New York, Minissota, Texas, Oklahoma, Arkansas, Mississippi, Alabama, Georgia, South Carolina, North Carolina, Tennessee, Indiana, Kentucky, Ohio, Virgina, New Jersey, Maryland). Heterodon nasicus is also found throughout Canada (Manitoba, Alberta, Saskatchewan) and the midwest United States (Colorado, Kansas, New Mexico, Montana, North Dakota, South Dakota, Nebraska, Oklahoma, Texas, Illinois). Heterodon simus is found in the southern United States (Mississippi, Alabama, Georgia,Florida, South Carolina, North Carolina, Virgina) (Uetz et al. 2019). Heterodon simus is most abundant in the lower coastal plain. This species has not been found in Alabama in over 15 years with the last recorded observation being in 1970.

Heterodon kennerlyi is found in the southern United States (Arizona, Texas, New Mexico) and Northern Mexico (Coahuila, Aguascalientes, San Luis Potosí, Nuevo León, Tamaulipas, Durango, Jalisco). (Uetz, et al., 2019b; Uetz, et al., 2019c; Uetz, et al., 2019d; Uetz, et al., 2019a)

Habitat

Heterodon platirhinos individuals are commonly found in areas with warmer soil, usually near wetlands with low canopy cover, but high shrub density, rock cover, and ground debris. Heterodon platirhinos individuals are usually found near wetlands because it contains their main food source, amphibians. Developed lands are also a main habitat for the eastern hognose because of the increased solar radiation and therefore increased ground temperature Heterodon simus individuals are usually found in sandy upland habitats and are also commonly observed crossing roads near shrub forests and old fields. They are usually associated with sandy soils and sand bridges, and are commonly found in pine-oak forests in North Carolina. Heterodon simus has been found burrowing up to 30 cm below the ground surface which is common making field observation a challenge. (Goulet, et al., 2015; Uetz, et al., 2019a)

Systematic and Taxonomic History

The name nasicus is derived from the Latin "nasus" meaning nose, in reference to the upturned snout. The subspecific name kennerlyi is a patronym in honor of Army Surgeon C.B.R. Kennerly. (Uetz, et al., 2019c)

Physical Description

Snakes in the genus Heterodon are known for their upturned snouts. Compared to other snake taxa, Heterodon species are relatively slow moving and stout bodied (Rouse et al. 2011). Heterodon simus has the smallest body size compared to the other species, and it is usually a tan color with dark brown blotches along its back and sides. Adults range in length from 33 to 56 cm with a max recorded length of 61 cm. Females tend to be larger than males. (Rouse, et al., 2011; Tuberville, et al., 2000)

  • Sexual Dimorphism
  • female larger

Reproduction

Female Heterodon platirhinos have been observed mating with multiple males during a season. (Cunnington and Cebek, 2005)

Heterodon simus lays eggs in clutches of six to 14. Eggs laid in captivity have an incubation period of 60-75 days to hatch. Not much research has been done on incubation of wild hognose eggs.

Heterodon platirhinos have a mean nesting temperature between 23.4 and 26.1 degrees Celsius and have an observed incubation time between 49 to 63 days. They usually lay their eggs in old mammal burrows, under rocks, in sawdust piles, or in small soil depressions. Copulation of H. platirhinos has been observed in both spring and fall in the southern range of habitat. (Cunnington and Cebek, 2005)

Female Heterodon are extremely specific to where they lay their eggs because the eggs are very sensitive to temperature change. Offspring laid in warmer nests are more likely to be larger and more developed at birth allowing for better survival rate. (Cunnington and Cebek, 2005)

Lifespan/Longevity

The lifespan of Heterodon nasicus are naturally limited by predators such as hawks, badgers and coyotes. Humans are also a cause of death for the hognose snake because of things like roads, agricultural machinery, insecticides, and loss of habitat. Lots of snakes are killed on roads because of increased traffic and loss of habitat causing hognose snakes to come into contact with humans more often. Farming equipment also causes the death of hognose snakes while they are burrowed under the ground or hiding above ground. (Didiuk and Wright, 1998)

Behavior

When threatened by a perceived predator all species of Heterodon will hiss, puff and strike followed by an intense writhing behavior that ends with a belly up position with mouth open and tongue out with no easily observed breathing. This behavior is known as death feigning and it is considered a way to startle and deter predators.

All species of Heterodon have evolved multiple fangs in order to subdue prey; the front fangs are used to grab while the back row of fangs inject prey with venom.

Heterodon platirhinos enters hibernation in November and emerges in March and are observed to be the most active in spring and fall. The eastern hognose are diurnal and crepuscular and present triphasic activity during part of the year. Heterodon nasicus enters hibernation in October and emerges in May and has been observed to be the most active in late spring and fall. The western hognose are only diurnal and show diphasic activity. (Kroll, 1973; Kroll, 1976; Kroll, 1997)

Communication and Perception

Heterodon nasicus uses visual and olfactory cues in order to locate and catch frogs and lizards. While H. platirhinos relies mostly on olfactory cues. All hognose snakes have touch corpuscles on their head shields and sensory pores on their dorsal body scales. (Kroll, 1973; Kroll, 1976; Kroll, 1997)

Food Habits

Heterodon platirhinos individuals eat invertebrate insects, such as crickets, beetles, grasshoppers, ants, wasps, and bees. They also eat vertebrates such as salamanders, green frogs, cricket frogs, toads, tadpoles, eastern fence lizards, ribbon snakes, lined snakes, mice, rodents, and chipmunks. Toads make up 40% to 75% of their diet. Heterodon nasicus individuals are more likely to eat animals other than amphibians compared to the other species in the genus. In captivity Heterodon platirhinos may get liver disease when placed on a complete mice diet. (Edgren, 1955)

Predation

Not much is known about natural predators of hognose snakes but humans play a large role in deaths of these snakes. Humans kill hognose snakes in the wild fearing they are venomous or confusing them with rattlesnakes because of their similar scale patterns. Reports of predation in the wild are rare, but it is assumed that predators of Heterodon species include larger snakes of other species, birds, large spiders, and predatory mammals.

To avoid predation Heterodon species use a complex series of defense mechanisms. They wiggle their tail, hiss, and flatten their necks. If harassed further, they turn onto their backs in a motionless position usually with the mouth open, feigning death. They may also defecate and vomit to further avoid predation. This death-feigning behavior in hognose snakes has also been observed with the snake repeatedly biting itself. Western hognoses (Heterodon nasicus) are the most docile in the genus and are least likely to show this behavior. (Durso and Mullin, 2013; Edgren, 1955)

  • Known Predators
    • humans (Homo sapiens)
    • predatory birds
    • predatory mammals
    • large spiders

Ecosystem Roles

Heterodon species prey primarily on toads. There is a correlation between locations of large toad populations and habitats of hognose snakes. Hognose snakes also hibernate in small mammal burrows or burrows dug themselves which loosens the soil and also can provide other organisms shelter in the future. In captivity, it is possible for hognose snakes to be infected with snake mites (Ophionyssus natricis). (Thomasson and Boulin-Demers, 2015)

Commensal/Parasitic Species
  • snake mites (Ophionyssus natricis)

Economic Importance for Humans: Positive

Northern hognose snakes (Heterodon platirhinos) has recently entered the pet trade while western hognose snakes (Heterodon nasicus) are the most abundant species of hognose within the pet trade. This is because western hognose snakes are the smallest of the other species and they are more flexible in their diet allowing for them to eat mammals other than amphibians, which are not available year round. Every state has different restrictions on selling and trading hognose snakes. (Averill-Murray, 2006)

  • Positive Impacts
  • pet trade
  • controls pest population

Economic Importance for Humans: Negative

Heterodon nasicus individuals possess large venom glands behind the rear fangs which have been observed to have the effect of immobilizing and killing its prey. Heterodon platirhinos also has these venom glands but they are not enlarged and have been concluded to produce no symptoms in humans. Several accounts of Heterodon bites have been reported in literature varying with severity. Bites to humans have been observed to cause edema, swelling, tenderness, and discoloration. (Averill-Murray, 2006)

  • Negative Impacts
  • injures humans

Conservation Status

Heterodon nasicus is a species of least concern, with a widespread and stable population. Heterodon simus populations have seen a sharp decline in range and population and are classified as vulnerable by the IUCN, and a species of concern by the U.S. Fish and Wildlife Service. Lack of documentation on Heterodon simus has caused it not to be listed as endangered, but multiple states have classified it as S3 or “rare or uncommon in state.” Heterodon nasicus is currently on the “blue list” in Alberta, Canada which means it is at risk of population decline. (Didiuk and Wright, 1998; Stallins and Kelley, 2013; Tuberville, et al., 2000)

  • IUCN Red List [Link]
    Not Evaluated

Contributors

Sarah Shassetz (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

agricultural

living in landscapes dominated by human agriculture.

aposematic

having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

scrub forest

scrub forests develop in areas that experience dry seasons.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

soil aeration

digs and breaks up soil so air and water can get in

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

References

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The Southwestern Naturalist
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