General Avoidance Information Regarding Rattlesnakes
April 27, 2011
Editor’s Note: The following information is reprinted from the June 23, 2010 issue of Life at Ken-Caryl.
The Western Rattlesnake (Crotalus viridis) is the only poisonous snake on the Ranch. It hibernates in subterranean
dens from late October to mid-April depending on weather and other environmental conditions. When rattlesnakes
emerge from their dens in the spring they are very active replacing depleted energy reserves and seeking a mate.
There may be concentrations of rattlesnakes around den sites as the snakes migrate and disperse.
Consider the following points for avoiding rattlesnakes in Open Space;
1. Rattlesnakes will use trails to hunt because their prey (primarily small rodents) use trails. Rattlesnakes lay in wait
for prey to pass at which point they strike and inject poison into their victim. Rattlesnakes, especially during cooler
temperatures, can be seen on trails and roadsides soaking up heat radiating from these warmer surfaces. Trail users
should be aware of these facts and always keep an eye on trail edges where these snakes could be hiding. Some
trails, like the North Hogback Trail, are mowed along the edges to provide better detection of any lurking snakes.
2. The North Hogback and Manor House Trails pass through Prairie Dog colonies. Rattlesnakes tend to be
concentrated in these areas because of the prey base. When in these areas be especially aware of the potential
presence of rattlesnakes.
3. Rattlesnakes are cold blooded, meaning their body temperature fluctuates with air temperatures. They have an
optimum temperature range that affects their activ ity. If temperatures are outside this range they will be less active.
Trail users often mistakenly assume that they can avoid rattlesnakes during the hottest days of summer by waiting
until evening to use the trails. Rattlesnakes will avoid the intense heat during the day opting to hunt during the cooler
temperatures of the evening.
4. Do not walk where you cannot see what is around you. Do not step over logs or rocks unless you can see what is
on the other side. Do not place your hands in cracks or ledges if you cannot see what is there.
5. Keep your pets on a leash. Keep small children near you. Dogs and children are curious and not always aware of
hazards and need to be watched.
6. Western Rattlesnakes are not aggressive. In most cases they will avoid confrontation by quietly crawling away.
They do not always “rattle” to warn humans of their presence. It is best to rely on your vision for avoiding encounters
For information on rattlesnake bite first aid, visit the Colorado State University Cooperative Extension Service Web
site at www.ext.colostate.edu. Look for the Coping with Snakes page in the natural resource section. Besides
information on treating bites, you will see tips on keeping snakes off your property. I thought the best advice from that
document regarding snakebites was, “The most useful snakebite first aid kit consists of car keys and cell phone for
calling the hospital and/or poison center.” At Ken-Caryl Ranch we are close enough to professional health care
facilities to get treatment within an acceptable amount of time.
Past Rattlesnake Control at Ken-Caryl Ranch
Ken-Caryl Ranch has always been and will probably always be terrific rattlesnake habitat. Concerns over conflicts
between new residents and rattlesnakes led to the creation of a rattlesnake control program in 1976. Four major den
sites were found. Since snakes hibernate en masse, often mingling with other species, the most effective way to
control the population is to collect the snakes while they are concentrated in these areas during the spring and fall as
they are dispersing and returning to the den sites. Between the summer of 1976 and the fall of 1979, 162 rattlesnakes
were either trapped or hand collected from three of the den sites. An additional 135 rattlesnakes were captured in
The control program was considered to be very effective, virtually eradicating rattlesnakes at two of the den sites. At
the largest den site located in the Dakota Hogback water gap along Massey Draw, 124 rattlesnakes were collected.
Despite the declining numbers of captured rattlesnakes from year to year at the den sites, the overall population was
still considered healthy. This situation led to speculation that there were many other smaller den sites that supported
much smaller hibernating populations of maybe 30 rattlesnakes or less. The only way that this theory could have
been supported would have been capturing, marking, releasing and re-capturing a considerable number of snakes
which was not a popular scenario with the client.
The information below is presented for general interest but should also be helpful in raising awareness about
rattlesnake behavior and activity for those that are interested in avoiding rattlesnakes.
Phenology of Rattlesnake Activities Over a One-Year Period at Ken-Caryl Ranch (from: Observations on Crotalus V.
Viridis (Rafinesque) and the Herpetofauna of the Ken-Caryl Ranch, Jefferson County, Colorado. Herpetological
Review, Volume 12, Number 2, June 1981. M. E. Ludlow)
January 1 to Late March
Snakes in hibernation, encounters very rare.
Late March to Late April
Basking at dens occurs when weather conditions are favorable. Most snakes re-enter the den each evening.
Late April to Late May
Snakes gradually begin to disperse from the denning areas onto summer ranges.
Late May to Mid-September
Snakes feeding, shedding, breeding, and giving birth on the summer ranges.
Mid-September to Early October
Snakes gradually begin to migrate back to dens.
Early October to Early November
Snakes arriving at the dens. Basking occurs when weather conditions are favorable.
Early November to December 31
Snakes in hibernation, encounters very rare.
Other highlights from the 1976-1979 control program:
• Efforts focused on control of the prairie rattlesnake (Crotalus viridis viridis)
• Adult viridis collected ranged from 28-34 inches in total length. The largest was 45 inches long.
• Rattlesnakes have been seen at den sites as early as 28 March and as late as 16
• Four major denning areas were found. All were in holes and crevices of sedimentary rock outcroppings.
• Rattlesnakes were most abundant in the prairie dog towns and on the hogbacks to the west. A few individuals were
collected on forested
northern slopes 7,500’ elevation but overall population density decreases as elevation increases.
• Temperatures must be at least in the mid-60s for the snakes to bask.
• Collected snakes were either donated to local universities for research or relocated (presumably off the property).
Avoiding Rattlesnakes at Home
You can reduce the chance of encountering rattlesnakes on your property by making your property as undesirable as
possible for them. For instance, be careful with pet food and bird seed; don’t let it lay around on the floor or ground.
This type of situation attracts small rodents which attracts rattlesnakes. Remove accumulations of leaf litter, firewood
piles and other types of cover. Keep your lawn mowed. Fill holes under patios and around your house foundation.
Consider putting an enclosure around the underside of a low deck; make sure that mesh openings are small, i.e.,
1/4”. Be wary of large rock clusters or dry stack, stone walls in your landscaping; these are very attractive to snakes.
by KCRMA Open Space Manager Sean Warren