SPECIES ACCOUNT. Eastern Milksnake / Couleuvre tachetée (Lampropeltis triangulum triangulum)
Department of Biology, Queen’s University, Kingston, ON Canada K7L 3N6
Taxonomy: Class: Reptilia. Order: Serpentes. Family: Colubridae. Genus: Lampropeltis. Species: Lampropeltis triangulum triangulum (Lacépède, 1788). (Lampropeltis means “shiny shield” (Tyning 1990) in reference to the smooth unkeeled dorsal scales (Logier 1958); triangulum comes from the Latin triangulus, meaning “triangle” and refers to the shape of the first blotch on the head of the Eastern Milksnake (Williams 1994). The common name comes from the false belief that milksnakes would enter barns at night and milk cows; however their jaw and needle-like teeth are unsuitable for sucking (Ernst and Barbour 1989).
Description: The Eastern Milksnake (Figure 1) is a slender medium-sized snake, up to 92 cm snout-vent length (Row and Blouin-Demers 2006a), with large brown or reddish brown dorsal blotches on a grey or tan (sometimes pinkish) background (Harding 1997). The blotches, ranging from 24-54 in number (Williams 1994), are outlined in black, and alternate with 1 or 2 rows of smaller dark blotches running down each side (Harding 1997). The ventral surface has a black rectangular checkerboard pattern on a grey, tan, or white background (Conant and Collins 1991, Christie 1997). Juvenile Milksnakes have brighter red or maroon coloured blotches on a pale grey background (Harding 1997; see Figure 2). Dyrkacz (1977) found that the colour of hatchlings maintained in captivity darkened with age. The scales are smooth and there are 19-23 scale rows at midbody (Harding 1997). The anal plate is not divided (Ernst and Barbour 1989), an attribute that can be used to distinguish the Milksnake from nominally similar species. The body of the Eastern Milksnake remains approximately the same diameter for its entire length (see Froom 1972). Its head is slightly pointed (Ernst and Barbour 1989) and only a little wider than the neck (Harding 1997). A light V- or Y-shaped blotch near the back of the head is a characteristic feature (Ernst and Barbour 1989), but as in other Milksnake subspecies, this patch is sometimes only a light ring around the neck (Conant and Collins 1991). There are no reliable external characteristics to distinguish male Eastern Milksnakes from females (Harding 1997). Like many snakes, sexually mature males usually have longer snout-vent lengths than females (Fitch and Fleet 1970). However, Fitch and Fleet (1970) found that the tail length of 64 male Milksnakes averaged 14.8% of the snout-vent length and this was not significantly different from the value of 14.5% of 49 females. In addition, no ontogenetic trend was found in relative tail length in Kansas Milksnakes (Fitch and Fleet 1970). The tails of females tend to taper quickly posteriorly, whereas males have tails that are thicker at the base, where the hemipenes are housed, before tapering towards the tip (Harding 1997). Sex may also be determined by probing the base of the tail for the presence of hemipenes.
Eastern Milksnakes are often confused with juvenile Racers, juvenile Black Ratsnakes, and Eastern and Western Foxsnakes. However, they can be distinguished readily in the hand because all the latter species have divided anal plates. In addition, Watersnakes may be confused with Eastern Milksnakes; however these have distinctly keeled scales, unlike the smooth unkeeled scales of the Eastern Milksnake (Harding 1997).
Distribution: Lampropeltis triangulum is one of the most widely distributed New World snakes and is found in North, Central, and South America (Lamond 1994). The Eastern Milksnake is the most northerly of 9 subspecies of milksnake found in North America and is the only Canadian subspecies (Bider and Matte 1996). In Canada, the Eastern Milksnake is found in Ontario and Quebec only. It is widespread in Ontario (Figure 3) and is locally common in some parts of southern Ontario (Fischer 2002). Populations of the species range as far north as Lake Nipissing and Sault Ste. Marie (Lamond 1994) and can also be found in most of the Great Lakes region but the species is missing in the northern and western watersheds of Lake Superior (Harding 1997).
In Quebec, the Eastern Milksnake ranges from the Ontario/Quebec border to Yamaska, southwest of Lac St. Pierre. However, records from Yamaska date back to 1874 so we do not know whether the population persists or has been extirpated due to urbanization (Froom, 1972). There has been only one record in the Quebec City area since 1958 (Bider and Matte 1996). The Quebec range is much more limited than that of Ontario and recent sightings only reaffirm their existence in the delineated distribution (Bider and Matte 1996).
Habitat: Milksnakes are commonly found in various habitat types such as rocky hillsides, bogs, marsh and swamp borders (Ernst and Barbour 1989), open prairies (Tyning 1990), and pastures and fallow farmland (Lamond 1994). It is a secretive subspecies and is most often found hiding under logs, rocks, or in the bark of old stumps rather than out in the open (Ernst and Barbour 1989). Some authors report that, in Ontario, Milksnakes occur most often in heavily forested areas (Lamond 1994). However, a recent radiotelemetric study of Milksnakes in eastern Ontario by Row and Blouin-Demers (2006a) suggests that Milksnakes preferentially occupy open and edge habitats as these provide characteristics that aid in thermoregulation (e.g solar radiation and a wide range of environmental temperatures). Open areas and edges also offer the opportunity for snakes to move between basking and shelter (Row and Blouin-Demers 2006b). Milksnakes do not often bask in direct sunlight but gain heat from under an object that is in direct sunlight, such as flat rocks, logs, stumps, boards, and strips of sheet metal (Fitch and Fleet 1970). In addition, Milksnakes prefer locations close to large rocks and boulders which serve as retreats for cooling and protection from predators (Row and Blouin-Demers 2006a). The preference for open habitat does not appear to change seasonally, even though the thermal quality of such habitats is higher in the summer than in spring and fall (Row and Blouin-Demers 2006b). Appropriate cover is required during the nesting and hibernating seasons. Eggs are often laid in rotting logs (Lamond 1994), compost, (Tyning 1990), mammal burrows (Ernst and Barbour 1989), or under suitable cover (Williams 1988). For hibernation, Milksnakes require a moist site to prevent desiccation over the winter and a temperature ranging from 4°-6°C (Fischer 2002). In Canada, they often hibernate in rock crevices (Tyning 1990) and even in basements of older homes in more populated areas where hibernacula have been lost due to habitat destruction (Johnson 1989).
Ecology: Mating season begins in early spring before dispersal from winter hibernation sites, lasting until late May and June (Harding 1997), with most copulations occurring in May (Ernst and Barbour 1989). Males can search for mates by following a scent trail left by females. During courtship, the male presses his chin against his mate’s back and coils his body around hers so as to bring their cloacas in contact, so that he can insert one of his hemipenes there. The male may also grasp the female’s neck in his jaws during copulation.
Milksnakes are oviparous with an incubation period of 30-40 days (Ernst and Barbour 1989). Females tend to lay their eggs in late June or early July (Harding 1997) and are often found in aggregations of several gravid females during the nesting season (Henderson et al. 1980). Females lay a maximum of one clutch a year, although Tryon (1984) reported that some female Milksnakes in captivity may produce more than one clutch annually. In fact, in the wild, individual female Milksnakes may actually reproduce no more often than every two years (Tyning 1990). The average clutch size of the Eastern Milksnake is 8-11 eggs, though it can range from 3-20 eggs (Lamond 1994). Ernst and Barbour (1989) reported that the number of eggs laid is directly correlated with the female’s body length. Eggs often adhere together forming clusters and hatch in late August or September, following an incubation period of approximately 6-9 weeks (Harding 1997). Hatchlings cut their way out of the eggs using an eggtooth on the tip of their snouts (Tyning 1990).
Sexual maturity in Milksnakes is reached around the third or fourth year after hatching (Harding 1997). Life spans for wild Milksnakes are estimated to be 7-10 years (Harding 1997). In their study of the natural history of Kansas Milksnakes, Fitch and Fleet (1970) found that the oldest snakes were 6-10 years old. One captive female Milksnake at a Philadelphia zoo survived an additional 21 years after being caught (Ernst and Barbour 1989).
According to Dyrkacz (1977), there is little growth between the time of hatching and emergence from hibernation in the spring, probably because the onset of colder weather inhibits surface activity and feeding (P. Gregory, pers. comm.). Dyrkacz (1977) found that Milksnake hatchlings collected in the spring in Illinois measured 25.2 cm TL (total length) and this is close to the average 24.8 cm TL upon hatching and 26.0 cm TL at one month after hatching.
Through most of its range, the active season of the Eastern Milksnake lasts from mid-April to late October or November (Harding 1997) although it may vary with latitude. In the southern part of its range around the Queen’s University Biological Station (QUBS), Eastern Milksnakes tend to be active between early May and early October (Row and Blouin-Demers 2006c). Milksnakes tend to remain underground or under cover much of the time and are largely nocturnal, especially during the warm summer months (Harding 1997). Dyrkacz (1977) found that most Milksnakes were undercover either early in the morning (0700-0900 hrs) or late in the afternoon (1800-2000 hrs); only one adult was found active during the day at 1000 hrs. Milksnakes have been found to share cover elements with other snake species such as Common Gartersnakes (Thamnophis sirtalis) and Northern Watersnakes (Nerodia sipedon) in southern Ontario (Gregory 2004). However, they were never found sharing cover objects with DeKay’s Brownsnake (Storeria dekayi), possibly because Milksnakes often feed on Brownsnakes in this region. Milksnakes hibernate, often communally, from late October or November to early April (Harding 1997).
There are few data on movements and dispersal of the Eastern Milksnake in Canada. Using the minimum convex polygon method of estimating home range sizes, Row and Blouin-Demers (2006c) found that the home range size of Eastern Milksnakes at QUBS ranged from 5.01 to 29.05 ha. One study by Fitch and Fleet (1970) on Kansas Milksnakes found that the home range covered approximately 20 hectares, assuming a circular shape. In the spring and fall, Milksnakes are often found in more upland areas than during the summer. It is presumed that they are moving to and from hibernating sites at these times of the year (Ernst and Barbour 1989).
Row and Blouin-Demers (2006b) found that the movement and thermoregulatory behaviour of eastern Ontario Milksnakes varied significantly across seasons. Snakes were found basking most in spring, travelling most in summer, and concealed most in the fall. By spending more time basking and less time travelling in the cooler spring, Milksnakes were able to achieve higher body temperatures. In the summer, less time is required for thermoregulation, allowing them more opportunity to forage, which requires longer movements.
The narrow body and small and delicate head and jaws of the Eastern Milksnake are not adapted for eating bulky prey (Fitch and Fleet 1970). Small mammals such as mice, voles, young rats, and shrews make up 70% of a Milksnake’s diet. The rest of the diet is comprised of other snakes, lizards, birds, and reptile and bird eggs (Harding 1997). Brown (1979) analyzed the stomach contents of 19 milksnakes (13 from Michigan and 6 from New York). Mammals made up 79.2% of the total food volume. Bird remains were found in only three stomachs and comprised 12.7% of the food volume. Reptiles ranked third, making up only 8.1% of the total food volume. Smaller prey are seized and swallowed alive, but larger animals are killed by constriction (Harding 1997).
The main predators of the Eastern Milksnake are larger mammals such as raccoons, coyotes, foxes, skunks, and opossums (in the south), as well as owls and hawks (Harding 1997). When it comes to defense, the Eastern Milksnake prefers flight to confrontation (Harding 1997). However, if threatened, it may vibrate its tail (Ernst and Barbour 1989) and take on a defensive pose with its head raised in the air and strike (Bider and Matte 1996). Some Milksnakes may bite and are difficult to remove as they bite hard and “chew” (P. Gregory pers. comm.). The sound of the vibrating tail against dry leaves or other objects is very similar to that made by a rattlesnake (Christie 1997). As such, it is presumed that this behaviour protects the Eastern Milksnake from potential predators by mimicking the sound of a rattlesnake (Lamond 1994). Some individuals may also spray musk or cloacal contents when disturbed or coil its body and attempt to hide its head under the coils (Ernst and Barbour 1989).
Conservation Status (from the Natural Heritage Information Centre):
Although the Eastern Milksnake appears to be common and apparently secure, there are several factors that may impact its persistence in Ontario and Quebec. These threats include habitat loss due to urbanization, road building, and habitat modification, land use practices such as forestry and agriculture, persecution (as they are often mistaken for venomous snakes), predation (especially by feral and domestic cats and dogs), and mortality on roads (Fischer 2002).
GRANK (global rank across the entire range): G5 = globally secure – very common; demonstrably secure under present conditions. GRANK DATE: 1996-10-30.
NRANK (national rank): N5 = nationally secure.
SRANK (provincial or sub-national level): S3 = widespread, abundant and apparently secure but with cause for long-term concern.
Ontario General Status: SECURE Ontario General Status Date: 01-Nov-99
Committee on the Status of Endangered Wildlife in Canada (COSEWIC): SC = special concern – due to the lack of data to support the claim that the Milksnake is secure, this is the recommendation until surveys are conducted that provide evidence to state otherwise.
There is currently very little information about the life history or population status of the Eastern Milksnake in Canada. Additional information on current and historical Eastern Milksnake habitat is required to determine whether or not it has changed – if indeed there exist sufficient historical data to do this. We still require basic population studies as none have been carried out thus far and several areas have not been surveyed (Fischer 2002); monitoring programs would help us to estimate population sizes, densities, and temporal population trends. Given that as many as 25 subspecies have been identified over the entire species’ range, a detailed phylogenetic and phylogeographic study would clarify affinities and genealogical distinctiveness of these forms. In addition, detailed gene flow studies might help in understanding dispersal patterns and the scale at which population differentiation occurs, given the retiring nature of this species.
In a study by Row and Blouin-Demers (2006a) on Milksnakes at QUBS, habitat use was strongly linked to thermal quality because the environmental conditions were thermally challenging in this northern locale. It would be interesting to conduct a study on habitat selection in relation to thermal quality in an environment that is less thermally challenging to determine how other factors, like food and predation risk, might shape behaviour. Finally, it would be worth undertaking a more comprehensive examination of how reproductive state, season, and level of disturbance influence habitat selection at multiple spatial scales (Row and Blouin-Demers 2006a).
Literature & Further Reading
- Bider, R.J. and S. Matte. 1996. The Atlas of Amphibians and Reptiles of Quebec. St. Lawrence Valley Natural Society, Sainte-Anne-de-Bellevue, Quebec and Ministère de l’Environnement et de la Faune, Direction de la faune et des habitats, Quebec. 429 pp.
- Brown, E.E. 1979. Stray food records from New York and Michigan snakes. American Midland Naturalist. 102: 200-203.
- Christie, P. 1997. Reptiles and Amphibians of Prince Edward County Ontario. Natural Heritage/Natural History Inc., Toronto, Ontario. 143 pp.
- Conant, R. and J.T. Collins. 1991. A Field Guide to Reptiles and Amphibians of Eastern and Central North America, Third Edition. Houghton Mifflin Company, Boston, Massachusetts. 366 pp.
- Dyrkacz S. 1977. The natural history of the Eastern milk snake (Reptilia, Serpentes, Colubridae) in a disturbed environment. Journal of Herpetology. 11: 155-159.
- Ernst, C.H. and R.W. Barbour. 1989. Snakes of Eastern North America. George Mason University Press, Fairfax, Virginia. 282pp.
- Fischer, L. 2002. COSEWIC Assessment and status report on the milk snake Lampropeltis triangulum in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 29pp.
- Fitch H.S. and R.R. Fleet. 1970. Natural history of the milk snake (Lampropeltis triangulum) in Northeastern Kansas. Herpetologica. 26: 387-396.
- Froom, B. 1972. The Snakes of Canada. McClelland and Stewart Limited, Toronto. 128 pp.
- Greene, H.W. 1997. Snakes The Evolution of Mystery in Nature. University of California Press. Berkeley.
- Gregory, P.T. 2004. Analysis of patterns of aggregation under cover objects in an assemblage of six species of snakes. Herpetologica 60:178-186.
- Harding, J.H. 1997. Amphibians and Reptiles of the Great Lakes Region. The University of Michigan Press. 378 pp.
- Johnson, B. 1989. Familiar Amphibians and Reptiles of Ontario. Natural Heritage/Natural History Inc. 168 pp.
- Lamond, W. G. 1994. The Reptiles and Amphibians of the Hamilton Area – an Historical Summary and the Results of the Hamilton Herpetofaunal Atlas. Hamilton Naturalists’ Club, Hamilton, Ontario. 174 pp.
- Logier, E.B.S. 1958. The Snakes of Ontario. University of Toronto Press, Toronto, Ontario. 94 pp.
- Oldham, M.J. and W.F. Weller. 2000. Ontario Herpetofaunal Atlas. Natural Heritage Information Centre, Ontario Ministry of Natural Resources. http://nhic.mnr.gov.on.ca/MNR/nhic/herps/ohs.html (updated 15-01-2010).
- Row, J.R. and G. Blouin-Demers. 2006a. Thermal quality influences habitat selection at multiple spatial scales in milksnakes. Ecoscience. 13: 443-450.
- Row, J.R. and G. Blouin-Demers. 2006b. Thermal quality influences effectiveness of thermoregulation, habitat use, and behaviour in milk snakes. Oecologia. 148: 1-11.
- Row, J.R. and G. Blouin-Demers. 2006c. Kernels are not accurate estimators of home-range size for herpetofauna. Copeia 4:797-802.
- Tryon, B.W. 1984. Additional instances of multiple egg-clutch production in snakes. Transactions of the Kansas Academy of Science. 87: 98-104.
- Tyning, T.F. 1990. A Guide to Amphibians and Reptiles. Little, Brown and Company, Boston. 400 pp.
- Williams, K.L. 1988. Systematics and Natural History of the American Milk Snakes, Lampropeltis triangulum. Milwaukee Public Museum, Milwaukee, Wisconsin. 258 pp.
- Williams, K.L. 1994. Lampropeltis triangulum (Lacepede) Milk Snake. Catalogue of American Amphibians and Reptiles 594: 1 – 594.
Reviewers: Jeffrey R. Row (Queen’s Univ.) and Patrick T. Gregory (Univ. of Victoria)
Published May 18, 2010.