Animal Diversity Web

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. (Wright and Wright, 1957)

• Biogeographic Regions
• nearctic
  • 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). (Johns, 2000; Shaw and Camp­bell, 1974; Wright and Wright, 1957)

• Habitat Regions
• temperate
• terrestrial

• Terrestrial Biomes
• savanna or grassland

• Range elevation

  90 to 2400 m

  295.28 to 7874.02 ft

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. ("West­ern Hog­nose Snake", 2000; Allen, 1997; Johns, 2000; Shaw and Camp­bell, 1974; Wright and Wright, 1957)

• Range mass

  80 to 350 g

  2.82 to 12.33 oz

• Range length

  36 to 93 cm

  14.17 to 36.61 in

• Average length

  50 cm

  19.69 in

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. (Shaw and Camp­bell, 1974)

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. ("West­ern Hog­nose Snake", 2000; Johns, 2000)

• Mating System
• 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. (Johns, 2000)

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

• Breeding season

  Breeding occurs in Spring and Summer.

• Range number of offspring

  4 to 23

• Average number of offspring

  13

  AnAge

• Range gestation period

  52 to 64 days

• Average age at sexual or reproductive maturity (female)
  Sex: female

  730 days

  AnAge

• Average age at sexual or reproductive maturity (male)
  Sex: male

  730 days

  AnAge

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. (Shaw and Camp­bell, 1974; Wright and Wright, 1957)

• 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. (Allen, 1997; Rolling Hills Zoo, 2001-2002)

• Typical lifespan
  Status: wild

  9 to 19 years

• Typical lifespan
  Status: captivity

  15 to 20 years

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 Snake", 2000; Rolling Hills Zoo, 2001-2002; Wright and Wright, 1957)

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. ("West­ern Hog­nose Snake", 2000; Johns, 2000)

• Key Behaviors
• terricolous
• fossorial
• crepuscular
• hibernation
• 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. (Rolling Hills Zoo, 2001-2002)

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. ("West­ern Hog­nose Snake", 2000; Allen, 1997; Shaw and Camp­bell, 1974)

• Communication Channels
• visual
• tactile
• chemical

• Other Communication Modes
• pheromones

• Perception Channels
• visual
• infrared/heat
• tactile
• acoustic
• 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. (Shaw and Camp­bell, 1974; Wright and Wright, 1957)

• Primary Diet
• 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. ("West­ern Hog­nose Snake", 2000; Rolling Hills Zoo, 2001-2002; Shaw and Camp­bell, 1974; Wright and Wright, 1957; "West­ern Hog­nose Snake", 2000; Rolling Hills Zoo, 2001-2002; Shaw and Camp­bell, 1974; Wright and Wright, 1957; "West­ern Hog­nose Snake", 2000; Rolling Hills Zoo, 2001-2002; Shaw and Camp­bell, 1974; Wright and Wright, 1957)

• Anti-predator Adaptations
• aposematic

• Known Predators

  • hawks (Accipitridae)
  • raccoons (Procyon lotor)
  • eastern spotted skunks (Spilogale putorius)
  • domestic cats (Felis silvestris)
  • domestic dogs (Canis lupus familiaris)
  • humans (Homo sapiens)

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). (Allen, 1997)

• Positive Impacts
• pet trade
• controls pest population

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

West­ern hog­nose snakes are docile and gen­er­ally do not harm peo­ple. (Allen, 1997; Mor­ris, 1985)

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. ("West­ern Hog­nose Snake", 2000; Allen, 1997; Johns, 2000; Rolling Hills Zoo, 2001-2002)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Federal List

  No special status

• CITES

  No special status

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).

Con­trib­u­tors

Nancy Shef­ferly (ed­i­tor), An­i­mal Di­ver­sity Web.

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

Ref­er­ences

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

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.