Scientific Name: Agkistrodon contortrix mokasen
Size: 24-36 inches (61-90 cm) in length
PA Status: Species of special concern
Habitat Type:
Deciduous forest, open fields and clearings (ofter near streams, but water is not a habitat requirement), rock crops, rock ledges, open habitat with rock and vegetation.
May be found under large logs, rocks, around brush piles rock crevices or slides.
Colorations:
Adults:
- The dorsal background is pinkish brown, light tan to greyish brown.
- The dorsal has wide brown to reddish brown bands that become darker towards the margin.
- The bands are saddle shaped (hourglass) that are broader along the sides and become narrower across the dorsum.
- Small dark spots are present inside the light area between the bands.
- The bands continue to the tail.
- Dorsal scales may have black flecks
- The ventral is cream to light brown with dark lateral blotches along the margin of the ventrals.
- The head is unpatterned with a reddish brown to bright coppery dorsal, and the lower half is usually lighter in color.
- The tail is yellow, green, or brown.
Juveniles:
- Similar to adults but with a bright green to sulfur yellow tail.
- Lack the black flecks on dorsal scales.
Characteristics:
- Medium-sized, heavy bodied species.
- The head is large, flat and triangular in shape.
- The head is distinct and set off from the body by a narrow neck.
- Pupils are vertically elliptical.
- The dorsal scales are keeled.
Scale Counts:
- 31 or 23 scale rows at midbody.
- 23 or 25 scale rows at anterior.
- 19 or 21 scale rows at posterior.
- 138-157 ventral scales
- 37-63 subcaudals scales | Single row of subcaudals
- 2 nasal scales
- 1 loreal scale
- 2-3 preocular scales
- 2-3 subocular scales
- 3-4 postoculars scales
- several temporal scales
- 8 supralabials
- 10 infralabials
- Anal plate is undivided
Confused with:
- Northern Water Snake
- Eastern Milk Snake
Coloration/Pattern Photos:
Adults
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Range Map:

References:
- Hulse, C. and McCoy C. J. and Ellen Censky ,1998. Amphibians and Reptiles of Pennsylvania and the Northeast. 346-350pp.
- Ernst, Carl H. and Ernst, Evelyn M. ,2003. Snakes of the United States and Canada. 473-480pp.
Photo Credits:
- Wayne Fidler
- Bob Bull
- Matt Nordgren