At one point the Milk Snake (Lampropeltis triangulum) comprised two dozen subspecies ranging from Quebec to Ecuador, from drab, saddled snakes to brilliant tricolours, and from bootlace-sized minatures to six-foot behemoths. The difference between a local Eastern Milk Snake and a tangerine-morph Honduran Milk Snake from the pet store is pretty extreme. It had been suggested, I can’t remember where, that the Milk Snake was an example of a ring species, where neighbouring populations interbreed but the end points (i.e., Quebec and Ecuador) are too distantly related.
But the simpler answer is that these snakes are not all one species, and a recent study—an early draft of which I tweeted about in December 2013—suggests that they are, in fact, seven species. The authors divide them as follows:
- Eastern Milk Snake (Lampropeltis triangulum), found in northeastern and central North America, includes the former Eastern (L. t. triangulum) subspecies and adds Louisiana Milk Snakes (amaura) from northeastern Louisiana and most populations of Red Milk Snakes (syspila). The Coastal Plains Milk Snake (“temporalis“), previously considered an intergrade between the Eastern Milk Snake and Scarlet Kingsnake (elapsoides), is also included.
- Western Milk Snake (Lampropeltis gentilis), found in the Great Plains and mountain states of the U.S., includes the New Mexico (celaenops), Central Plains (gentilis), Pale (multistriata) and Utah (taylori) Milk Snakes, as well as most Louisiana Milk Snakes (amaura), Mexican Milk Snakes (annulata) from central Texas and Red Milk Snakes (syspila) from Kansas, Nebraska and Oklahoma.
- Scarlet Kingsnake (Lampropeltis elapsoides), found in the southeastern U.S., is unchanged.
- Tamaulipas (Mexican) Milk Snake (Lampropeltis annulata) includes Dixon’s Milk Snake (dixoni) and most populations of the former Mexican subpsecies (annulata), and is found in northeastern Mexico and Texas.
- Mexican Milk Snake (Lampropeltis polyzona) includes the former Jalisco (arcifera), Pueblan (nelsoni), Sinaloan (sinaloae) and Smith’s (smithi) subspecies, as well as some populations of the Conant’s (conanti) and Atlantic Central American (polyzona) subspecies. It’s found in central Mexico.
- Central American Milk Snake (Lampropeltis abnorma) includes the Guatemalan (abnorma), Blanchard’s (blanchardi), Honduran (hondurensis), Pacific American (oligozona), Stuart’s (stuarti) subspecies, as well as some populations of the Conant’s (conanti) and Atlantic Central American (polyzona) subspecies. It’s found from southeastern Mexico (Guerrero, Veracruz) to Costa Rica.
- South American Milk Snake (Lamproletis micropholis) includes the Andean (andesiana), black (gaigae) and Ecuadorian (micropholis) subspecies. It’s found in Colombia, Costa Rica, Ecuador, Panama and Venezuela.
I’m no herpetologist, but to my amateur eyes this makes considerable sense, and upends a taxonomical paradigm that was clearly unsustainable. Whether this one holds, or is refined further, is anyone’s guess.
If nothing else, it’ll make things more clear in the pet trade, especially here, where Eastern Milk Snakes are a local, protected species (and lousy captives, to boot), whereas Mexican and Central American Milk Snakes are in every pet store. Strictly speaking, as (former) members of Lampropeltis triangulum, they were illegal, though in practical terms they were obviously not local snakes. Now the letter and spirit of the law can be more closely aligned.