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Bio 164 (Herpetology)
Instructor: Dr. William Avery
http://www.csus.edu/indiv/a/averyw/
Snakes of the Western United States:
Their Natural History and Ecology
Summary of a presentation given to the Herpetology class by Gerold Merker
| A. | Introduction | |
| Speaker: Gerold
Merker Range of species in talk: Western United States - as far east as Montana, Wyoming, Colorado, and Texas. Emphasis will be on local species |
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| B. | General Description | |
| 1. | Snakes are elongate, limbless animals with a clear spectacle covering over the eye and no external ear opening. Class: Reptilia Order: Squamata | |
| 2. | Snakes are thought to have evolved from a fossorial form, in the process losing their eyelids, external ear openings, and appendages. | |
| 3. | Snakes range in size worldwide from approximately 10 cm in total length to perhaps as long as 9+ meters. | |
| 4. | Snakes utilize their tactile sense and smell in a world that is very low to the ground. They are able to pick up low frequency airborne sounds which are transferred through the substrate into the middle and inner ear of the snake. | |
| 5. | Eye shape: elliptical vs. round - nocturnal vs. diurnal | |
| C. | Diversity | |
| 1. | Colubrids represent by far the most species of snakes found in the United States. | |
| 2. | Families represented in the Western United States include: Leptotyphlopidae, Boidae, Colubridae, Elapidae, Hydrophiidae, and Viperidae | |
| 3. | California has a total of: 1 in Leptopyplopidae, 2 in Boidae, 28 in Colubridae, 1 in Hydrophiidae, and 6 in Viperidae (38 species total) | |
| D. | Thermal Requirements | |
| 1. | Temperatures influence bodily functions (e.g., digestion, ecdysis) | |
| 2. | Extreme temperatures are dangerous for snakes due to their elongate shape - the surface area to volume ratio in snakes is such that they heat up rapidly. | |
| 3. | Snake optimal operating temperature is approximately 30 °C. | |
| 4. | Thermal requirements determine, along with moisture levels, where the snake is likely to be. | |
| E. | Feeding | |
| 1. | Prey items in the wild in our area include earthworms, slugs, crayfish, insects, centipedes, scorpions, ants, termites, cicadas, grasshoppers, crickets, fish, frogs, salamanders, turtles, birds, lizards, other snakes, reptile eggs, and mammals. | |
| 2. | Snakes have a loosely constructed skull designed for facilitation of feeding on large prey items. Snakes lack the fused anterior mandibles of other vertebrates; instead they have a number of ligaments connecting the lower mandible, allowing each mandible to move independently. | |
| 3. | Feeding is accomplished in most snakes by the incredibly mobile upper jaw and the wide range of movement in the lower mandible. | |
| 4. | There are several methods of feeding including: overpower and engulf, constrict and engulf, and envenomate and engulf. | |
| 5. | A black-tailed rattlesnake (Crotalus molossus) needs only two meals per year to survive. | |
| F. | Reproduction | |
| 1. | Males and females resemble one another in most snakes (one notable exception are boids) - in general, males have a proportionally longer tail than do females. | |
| 2. | Oviparous snakes lay shelled eggs. | |
| 3. | Ovoviviparous snakes retain eggs in the body until they hatch. | |
| G. | Conservation | |
| Man impacts snake populations by habitat destruction, including pesticide use, and by roadways. | ||
| H. | Animals Brought in for Display | |
| 1. | Rubber Boa (Charina bottae): Female from El Dorado Co., California. One of two boids found in the United States. | |
| 2. | California Kingsnake (Lampropeltis getula californiae): Male from Sacramento Co, California. This animal has been in captivity over 15 years. | |
| 3. | Banded or Variable Sand Snake (Chilomeniscus cinctus): This animal is from Maricopa County, Arizona. These sand swimmers are highly specialized for their habitat. | |
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 Students listen to Gerold Merker as he presents "Snakes of the Western United States" |
Your questions, comments and suggestions
are welcome. E-mail Jana