Heterodon kennerlyi vs Heterodon nasicus

Written by: Reptiles Breeding Enterprise

Originally there were three different subspecies in the western hognose snake.

Heterodon nasicus nasicus
Heterodon nasicus gloydi
Heterodon nasicus kennerlyi

The subspecies status for "Gloydi" dropped quickly and without prolonged discussions and these animals now have a local form status. Unfortunately, there are only very little information about these animals.

Since 2003 "Kennerlyi" (also called Mexican hognose snake) are recognized as separate species, at least in the US. Unfortunately, there is very little information and pictures out there, how to tell the Kennerlyi apart from Nasicu without any doubt. What makes it difficult is the fact that animals of the southern area of ​​distribution of Heterodon nasicus were offered as "Kennerlyi". This has contributed to the current point that many breeders keep Western hognoses(insteat of Mexicans) or Kennerlyi-Nasicus hybrids than pure Kennerlyies unknowingly.

The two different species, Heterodon nasicus and Heterodon kennerlyi, differ from each other in the pattern and the scale counts on the head. Since the description of patterns can often be quite confusing, I do this in connection from words and pictures. 
As for the scales on the head...special attention is given to two groups. One group is the Loreal scales. These are located directly above the Supralabiale scales, and between the nasal scales and the präoculare scales. The other group is the azygos scales. This is a group of small scales, which are located directly after the rostral scale (the hooked scale, which is the reason for the name of this groupe of snakes) on the top of the head and among the prefrontal scales.

But now the pure numbers:

Heterodon kennerlyi has a total number of 0-2 loreal scales and 2-6 azygos scales.
Heterodon nasicus has a total number of 3-9 loreal scales and 9-27 azygos scales.

There are also dissenters in the numbers of the scale counts within each species itself. But these are rar, with an incidence of less than 5%. So if you look on both scale groups together, it has a more than reliable differentiation basis. Especially if you keep in mind that 99% of "Nasicus" have 9 or more azygos scales, but less than 3% of the "Kennerlyies" have more than 8 azygos scales. Making it possible to build following little mnemonic: 
small scaled head = "Nasicus" 
large scaled head = "Kennerlyi"
Heterodon kennerlyi
 Heterodon nasicus