Eastern Hog-nosed Snake (Heterodon platirhinos) COSEWIC assessment and update status report: chapter 6

• Previous page
• Table of contents
• Next page

Biology

Feeding

Eastern Hog-nosed Snakes appear to hunt mainly by olfaction, and feed on toads, frogs, or lizards (Platt 1969). Although these prey as well as insects, other amphibians, molluscs, birds, crustaceans, turtles, earthworms, and spiders (Hamilton and Pollack 1956, Mills and Yeomans 1993) have been recorded as part of the diet of H. platirhinos in the U.S., adult snakes in the wild in Canada are only known to feed on toads (Bufo americanus andB. fowleri) (J. Rouse and G. Cunnington pers. comms.). Juveniles feed upon smaller prey such as juvenile toads, Redback Salamanders (Plethodon cinereus), Spring Peepers (Pseudacris crucifer), or invertebrates (Michener and Lazell 1989). It is also unclear as to whether some of the aforementioned invertebrate prey items were secondarily ingested, or whether the difference between the Canadian populations of Eastern Hog-nosed Snakes and the ones from the U.S. is due to differing prey availability or preference. Captive H. platirhinos only reluctantly feed on, and usually have to be force-fed, any food other than live toads (Schueler 1997). However, in some cases, a good feeding response to other species (e.g. mice) can be induced by rubbing them with a toad (S. Gillingwater pers. comm.).

Observations of H. platirhinos feeding in the wild in Ontario have been recently recorded and described. It has been observed that once the snake has found the scent trail of a toad and has visually located it, it essentially charges at its prey as quickly as it can with a gaping mouth. If the snake successfully catches the toad, it often also has debris in its mouth, such as bits of twigs and leaves (G. Cunnington pers. comm.). If a toad inflates itself during the feeding process the snake can deflate it by piercing it with its rear fangs, which can also deliver mildly venomous secretions from the Duvernoy’s glands (Young 1992). The Eastern Hog-nosed Snake has been described as an awkward, slow, clumsy feeder, and therefore may have difficulty catching faster prey such as frogs and small mammals (G. Cunnington pers. comm.). The apparent tolerance of the Eastern Hog-nosed Snake to the toxins in toads has not been investigated, but it may confer protection to the snake from its own predators (Greene, 1997).

Life cycle and reproduction

According to Harding (1997), H. platirhinos reaches maturity at 2-3 years of age and has been known to live to 11 years in captivity, although these observations are from specimens in the U.S.  Since Ontario represents the northern portion of this species’ range, age at maturity for snakes in Canada may be as high as 4-5 years of age (Seburn 2005). Generation time can be estimated as Gen Time=age 50% maturity + 1/M where M = natural mortality rate. Thus, GT= 4 + 1/0.40 = 6.5 years.

In a study conducted in 2005 in Wasaga Beach Provincial Park, most sightings of copulation occurred between August 7^th and September 17^th, although one mating pair was seen copulating as early as May 14^th (Cunnington and Cebek 2005). According to the same study, males actively seek out females and follow them for hours while engaging in courtship behaviour; the males rub themselves along the female’s body and if the female is receptive, the mating pair may be linked in copulation for up to 3 days. During September, one female was seen mating with 5 of her 9 suitors with copulations occurring 1-6 days apart. Mating was also observed between August 7^th and September 18^th in a population located near Parry Sound (Rouse 2006). In this population located on the Canadian Shield, most copulations observed occurred at the end of August and in September, although copulations have also been recorded in the spring in other areas (Harding, 1997; S. Gillingwater pers. comm.), particularly in the U.S.A.

The Eastern Hog-nosed Snake is oviparous; females lay eggs in nests up to 20 cm below the surface in sandy soil (Platt 1969, Cunnington and Cebek 2005), or under driftwood, partially buried in sand (S. Gillingwater pers. obs.). Oviposition can occur anytime during a 2-3 week period beginning in late June (Cunnington and Cebek 2005, J. Rouse pers. comm.). In Canada, at the northern portion of the species’ range, females may be required to excavate nests in locations that provide enough sunlight to ensure proper thermal conditions for incubation of the eggs (Cunnington and Cebek 2005). Therefore, females carefully choose oviposition sites by probing the ground with the tip of their rostra and often abandon excavation sites if improper conditions are encountered (Cunnington and Cebek 2005). Communal nesting has been reported only once for this species (in Wasaga Beach P.P., Cunnington and Cebek 2005). As Magnusson and Lima (1984) point out, communal nesting in snakes may be a consequence of a limited number of suitable oviposition sites, and cued by chemical cues produced by conspecifics that indicate a suitable site. Although the number of observed communal nests is small, this seems a likely explanation in the Wasaga region because there is little suitable oviposition habitat found in Wasaga Beach Provincial Park (only 1.3% of the total available area). Hog-nosed Snakes on the Canadian Shield sometimes lay eggs in sandy nests but have also been observed to nest in cavities under rocks (J. Rouse pers. comm.). In addition, the Eastern Hog-nosed Snake shows high nest site fidelity from year to year (observations from Wasaga Beach Provincial Park, G. Cunnington pers. comm.). In one case, however, where an old agricultural field was restored (in south Walsingham), potentially as many as 20 Eastern Hog-nosed Snakes nested over the span of 2 days in June of 2006 (M. Gartshore pers. comm.), apparently attracted by freshly tilled sandy soil.

The clutch size for this species, in all its range except for Ontario, averages 19-23 eggs (Schueler 1997). Data from natural nests in Ontario come from only four nests from Wasaga Beach Provincial Park, numbering 7, 12, 27, and 28 eggs (Cunnington and Cebek 2005), and a small number of nests from Parry Sound, numbering between 17 and 37 eggs (J. Rouse pers. comm.). The average number of eggs from 10 Ontario clutches laid in captivity, however, averaged 35.5 with half the clutches numbering 40 or more eggs (Schueler 1997). Also, the snake from Parry Sound that laid 37 eggs did so prior to release, after spending 3 days in captivity. The large difference between the number of eggs from clutches in natural settings and ones laid in captivity is unexplained and not discussed in the literature. One possible explanation is that these snakes lay more than one clutch in the wild and that the conditions of captivity force or induce them to lay all their eggs in one place (K. Beriault, pers. hypothesis).

There is little information available regarding hatching success of eggs of H. platirhinos in Ontario. The only study that measured this found that hatching success of three nests in the wild was 33.3%, 57.1%, and 74.1%, and hatching success of a nest incubated in a laboratory was 85.7% (Cunnington and Cebek 2005). The hatching success of the eggs of the female that laid her clutch in a bag was 100%; these eggs were also incubated in the laboratory. The average number of days to hatching of nests in the wild is 58 (n=3, Cunnington and Cebek 2005), and hatching occurs in late August and early September.

Eastern Hog-nosed Snakes probably don’t hibernate communally, may or may not excavate their hibernation site depending on the availability of appropriate pre-made sites such as burrows (Plummer 2002), and may or may not exhibit hibernation site fidelity. Also, hibernation sites may be a natural source of mortality if the ambient temperature falls below the freezing level as snakes had body temperatures approximating the temperature of the hibernaculum (Plummer 2002). In one Ontario study, the species hibernated from October to April (Cunnington 2004a).

Predation

Eastern Hog-nosed Snakes probably experience high mortality from predation presumably because they are active predators and are naturally a highly vagile species. Predation rates have been estimated at 40% of the adult population per year (Cunnington 2006; J. Rouse pers. comm.). The major predators on the nests are mustelids, foxes, and other medium-sized mammals such as raccoons. Raptors and wild turkeys (see Fig. 6) are also predators of juveniles and adults. Pet and feral cats and dogs are also likely predators (S. Gillingwater pers. comm.) although in some locations humans are responsible for many snake deaths.

Eastern Hog-nosed Snakes have developed an unusual adaptation to predation which consists of complex defensive behaviour. When approached by a predator this snake has a tendency to inflate its neck to a cobra-like hood, hiss, and strike, usually with mouth closed, eventually defecate and cover itself with foul-smelling (as opposed to the sweet type) excrement, roll onto its back (see Figure 6), open its mouth with its tongue flopping out, and possibly even exude blood from its mouth and\or cloaca (Harding 1997). This seems to be a poor strategy, and certainly is if humans are the threat. However, it is possible that the toxins ingested from the snake’s diet of toads provides protection either as toxin or by providing olfactory cues that repel predators from toads (R. Brooks pers. comm.). This is a strategy analogous to that used by some molluscs that incorporate the stinging threads (nematocysts) of their cnidarian prey for their own defence.

Physiology

The average incubation temperature of the three nests from Wasaga Beach P.P. was 24.8 °C with one nest having both the lowest and highest recorded temperatures  (13.0 °C and 37.8 °C; n=3, Cunnington and Cebek 2005). The female equipped with a temperature-sensitive transmitter had an average body temperature of 30.5 °C (±1.0 °C) throughout oviposition.

Eastern Hog-nosed Snakes probably use grass habitat and sand pits, more than they do forest and wetlands (Rouse 2006), to regulate their body temperature as well as to find suitable prey.

Interspecific interactions

There is no literature on the interaction of H. platirhinos with organisms other than toads, but unidentified parasites have been seen in the mouthes of some individuals and they can also be infested by mites (S. Gillingwater pers. obs.). In addition, Eastern Hog-nosed Snakes have been seen under cover material with Five-lined Skinks (Eumeces fasciatus) at Rondeau P.P. and will share underground networks of tunnels with mice and foxsnakes (Elaphe gloydi) at Long Point P.P. (S. Gillingwater pers. obs.). Eastern Hog-nosed Snakes historically occurred at all sites along Lake Erie in Ontario where Fowler’s Toad, Bufo fowleri, was found (Schueler 1997). At Point Pelee and Pelee Island, where Fowler’s Toad has apparently disappeared (Green 1989), the Eastern Hog-nosed Snake populations have also vanished even though Bufo americanus remains common (Schueler 1997).

It has been hypothesized that the snakes’ spatial and temporal distribution in the various types of habitats (riparian, forest uplands, etc.) can be explained by the seasonal movement of their only source of food, toads (G. Cunnington pers. comm.). If this interaction exists and if it is further examined, it may provide insight as to the best approach for the conservation of H. platirhinos. 

Adaptability

Eastern Hog-nosed Snakes survive in a variety of habitats, although these areas are always found near open sand pits (J. Rouse pers. comm.). They also seem to persist in urban areas, although populations in these areas suffer high rates of mortality and have a male-biased sex ratio (G. Cunnington pers. comm.). The data indicate that this species experiences an annual adult mortality rate of 40% (Rouse, 2006, J. Rouse pers. comm.; Cunnington, 2006, G. Cunnington pers. comm.), similar to a rate of 50% reported by Plummer and Mills (2000) for an American population. In Wasaga Beach P.P., 38% of mortality is human-caused (G. Cunnington pers. comm.).