Snakes are long, slender, legless reptiles. They 

have unblinking eyes and move forward by 

undulating from side to side. Snakes are carnivorous and 

swallow prey whole. After eating, snakes generally rest, 

seeking sites where they can stay warm and digest their 

meal. There are 26 species of snake in Colorado and 10 

have been documented at Bent’s Old Fort.

The plains garter snake has pale stripes on the sides 

of the body and a bold orange stripe along its back. 

This snake is generally found in the vicinity of water in 

eastern Colorado and its diet includes earthworms and 

amphibian larvae.

The prairie rattlesnake is easily identifiable by the 

horny rattle at the tip of its tail. Although it occupies 

most of its historic range in Colorado, persecution by 

humans is a threat to this snake. 

The bullsnake (front cover) is often encountered and 

is widespread in Colorado. Bullsnakes eat rodents and 

are highly beneficial to farmers and ranchers.

Lizards

 

 

Woodhouse’s toad. 

Photo by D. Troyer. 

Great plains skink. 

Photo by C. Schwalbe. 

Western terrestrial 

garter snake eating 

vole. Photo by 

E. Muths. 

Plains garter snake and Prairie rattlesnake. 

Photos by D. Troyer.

—Lt. James W. Abert, U.S. Army, 2 September 1846, 

 at Bent’s Old Fort.

Six-lined racerunner. 

Photo by G.A. Hammerson

Texas horned lizard. Photo by C.W. Brown.

All lizards in Colorado have a long tail. In many species the tail is detachable, providing the 

animal with an escape mechanism when attacked. The 

detached tail continues to wriggle while the owner flees. 

All Colorado lizards depend on insects as their main food 

source. Four of the 19 species that occur in Colorado 

have been documented at Bent’s Old Fort. 

The Great Plains skink has smooth, shiny, tightly 

overlapping scales with rounded, dark edges. It is a 

secretive species but is fairly common throughout its 

historic range in Colorado, and is often found under 

rocks, logs, and other ground debris.

The six-lined racerunner lives up to its name, moving 

up to 29 km (18 miles) per hour when approached. It 

has three pale stripes along each side and small granular 

scales. The neck and shoulders of adults are often bright 

green. They are locally common in eastern Colorado.

Texas horned lizards (likely the subject of the quote 

above) are found at Bent’s Old Fort but are secretive. 

These lizards are recognizable by their wide and 

flattened body and characteristic spines on the back of 

their head. While fairly common in their historic range in 

Colorado, collecting poses a threat to this species.

Juvenile snapping turtle.

Photos by D. Troyer.

 “There are 5 different varieties of the terrapin 

 or turtle.”

 —Lt. James W. Abert, U.S. Army, 4 September 1846, 

 at Bent’s Old Fort.

Chorus frog. 

Photo by 

R. Scherer. 

Tiger salamander. Photo by J.D. Willson.

There are three groups of amphibians occurring worldwide. Two of these groups occur in 

Colorado: 1) Frogs and toads, and 2) salamanders. Four 

species of frogs and toads and one species of salamander are found at Bent’s Old Fort. 

Amphibians are ectotherms, acquiring body heat 

from their surrounding environment. They have moist 

skin with mucous glands that are often poisonous. 

Amphibians in Colorado experience temperature 

extremes: freezing-cold winters and scorching-hot 

summers. They cope in a variety of ways, including 

seeking microenvironments (such as underground 

burrows) that protect against harsh outside temperatures. 

Woodhouse’s toads have a light stripe down their 

back and parallel cranial crests (little ridges) between 

their eyes. They are widespread and often encountered 

at Bent’s Old Fort.

Many species of amphibians have distinctive calls. 

The visitor is likely to hear chorus frogs calling in the 

wetlands around Bent’s Old Fort in the spring. The call 

of the chorus frog has been compared to the sound of 

running a finger over the teeth of a comb!

Tiger salamanders are abundant in Colorado but are 

generally more secretive than frogs and don’t vocalize. 

Tiger salamanders are sometimes found in the irrigation 

ditches at the fort.

Amphibians

(Frogs, Toads and Salamanders)

Snakes

Spiny softshell turtle.

“One of these Indians possesses an antidote for 

the poison of the “she-she-note” or rattlesnake 

and has frequently brought them [snakes] into the 

Fort...Whenever anyone is bitten he spits this juice 

on the wound and they get well.”

Turtles

“ The day was extremely windy, the road dusty, 

the country around sterile. The sage, greasebush, 

and yucca linearifolia among the plants, and the 

horned frog with the hare and antelope, were the 

only objects I noticed.” 

 —Lt. James W. Abert, U.S. Army, 10 September 1846, 

 one day west of Bent’s Old Fort.

Turtles carry their home on their back in the form of a shell, a bony structure made of hardened skin usually covered by horny plates. The ribs are 

incorporated into this shell. 

There are five species of turtle in Colorado, and 

three have been documented at Bent’s Old Fort. Turtles 

eat a variety of plants and animals, but in Colorado they 

feed primarily on invertebrates and other animal matter. 

The spiny softshell turtle has a flattened shell with 

flexible edges. The forefoot has 3 claws. This turtle 

is sensitive to disturbance of nesting areas through 

land-use changes or the presence of humans during the 

nesting season.

The snapping turtle spends most of its time underwater. The rear edge of the shell is sawtoothed and, in 

juveniles, the shell has three ridges that smooth as the 

turtle ages. Snapping turtles are a small-game species 

(with a license) in Colorado. 

The Ornate box turtle, observed but not officially 

documented at the fort, has a hard, domed shell with 

yellow spots or streaks. The shell is hinged in adults 

allowing the turtle to completely shut itself up in a 

“box”. This species is locally common in portions of 

the Arkansas River. Ornate box turtles are listed as 

a CITES* Appendix II species meaning that trade in 

these turtles is strictly controlled. 

*Convention on International Trade in Endangered Species of Flora 

and Fauna.
Amphibians, Reptiles, 

and Conservation

Amphibians and reptiles are two groups of animals that are experiencing unprecedented declines 

around the world. Serious declines have been noted in the 

United States (for example, Drost and Fellers, 1996) and 

even in Colorado (Muths and others, 2003).

Although most of the species at Bent’s Old Fort 

National Historic Site are not threatened or endangered, 

their local range and abundance have likely declined 

since settlers arrived and began the massive conversion 

of native prairie to agricultural lands. The destruction of 

habitat is arguably the most common cause of population 

decline worldwide (Lannoo, 2005) and has likely affected 

the herpetofauna at Bent’s Old Fort. 

Accounts of nearly all the species occurring around 

this site note that human activity has had a negative 

impact on population sizes (Hammerson, 1999). The 

magnitude of the effect is unknown because there is no 

information on the presence or abundance of amphibians 

in Colorado prior to 1833. 

Small parks, such as Bent’s Old Fort National Historic Site, often act as important reservoirs of safe habitat and may play important roles in the conservation of 

amphibians and reptiles across the landscape. 

Of the animals known to be present at Bent’s Old 

Fort, Texas horned lizards may be the most vulnerable, 

primarily because humans often capture them and take 

them home as pets. This is illegal throughout Colorado 

without appropriate permits!

Drost, C.A., and Fellers, G.M., 1996, Collapse of a regional frog 

fauna in the Yosemite area of the California Sierra Nevada, USA. 

Conservation Biology v. 10 p. 414-425.

Hammerson, G.A., 1999, Amphibians and reptiles in Colorado, 

2nd edition, University Press of Colorado and Colorado Division 

of Wildlife.

Lannoo, M. 2005. Amphibian Declines, The Conservation Status of 

United States Species. University of California Press, Berkeley.

Muths, E., Corn, P.S., Pessier, A., and Green, D.E., 2003, Evidence 

for disease-related amphibian decline in Colorado. Biological 

Conservation v. 110 p. 357-365.

Printed on recycled paper

For more information on:

 The herpetofauna of Bent’s Old Fort -

http://www.nps.gov/beol/naturescience/animals.htm

Amphibian decline - http://armi.usgs.gov/

Amphibian calls - “Sounds of North America Frogs”

Charles M. Bogert, 1998 Smithsonian Folkways Recordings, SFCD 45060