Helminth Parasites of the Prairie Rattlesnake, Crotalus viridis Rafinesque, 1818, in Weld County, Colorado

Abstract

Examination of 204 Crotalus viridis Rafinesque, 1818, from three locations in Weld Co., Colorado, yielded the following species of helminths: Kalicephalus inermis coronellae Ortlepp, 1923, Rhabdias sp., Physaloptera sp. (third-stage larvae), and Oochoristica osheroffi Meggitt, 1934. Rate and mean number of parasites per individual were recorded. The prairie rattlesnake, Crotalus viridis Rafinesque, 1818, is available in large numbers in Weld Co., Colorado. Klauber (1956) reported that C. B. Perkins caught 863 rattlesnakes near Platteville, Colorado, during the years 1930 to 1932. In 1961, 360 individuals were destroyed in 3 days by ranchers in northeastern Weld Co. (Castor, pers. comm.). Examination of snakes from southern Weld Co. showed a rich helminth fauna; and since virtually no information was available on parasitism of C. viridis, additional studies were made. MATERIALS AND METHODS Prairie rattlesnakes from three sites in Weld Co., Colorado: Keenesburg, Sec. 16, T 2N, R 64W; Platteville, Sec. 16, T 3N, R 65W; and Nunn, Sec. 16, T 8N, R 67W, were captured during October and November 1961 to 1963 and April and May 1962 and 1963. The snakes were killed by means of an injection of a solution containing sodium pentobarbital as the active ingredient. They were weighed, measured, and examined for intestinal helminths. The coelom was opened by making a midventral incision from the cloacal vent to the neck. The lungs, stomach, small intestine, large intestine, cloaca, and gall bladder were separated and placed in separate petri dishes for further examination. Nematodes removed from the gut were killed and fixed in hot 70% alcohol, cleared slowly in glycerine-alcohol, and mounted in glycerine. Cestodes were relaxed in lukewarm distilled water for 1 to 2 hr and fixed in A.F.A. for 24 hr. After fixation, the specimens were stained with Ehrlich's acid hematoxylin and modified Mayer's HC1 carmine (Meyer and Penner, 1962), cleared in xylene, and mounted in Cambol. RESULTS AND DISCUSSION The majority of snakes used in this study came from the Keenesburg site (Table I). All of the collection areas were active or abanReceived for publication 22 June 1966. doned prairie dog towns. The Keenesburg site, however, is the only area in which cattle did not graze during the years 1960 to 1964, and thus it was relatively undisturbed. The four species of helminth parasites collected were: Kalicephalus inermis coronellae Ortlepp, 1923, from the stomach and small intestine, Rhabdias sp. from the lungs, Physaloptera sp. (third-stage larvae) from the stomach and small intestine, and Oochoristica osheroffi Meggitt, 1934, from the small intestine. Since none of the species collected during the survey had been previously reported from prairie rattlesnakes, these observations constitute new host records. Schad (1962) reported that K. inermis coronellae exhibits habitat specificity in being confined to the esophagus in all snakes examined immediately after death. He attributed the occurrence of this parasite in the small intestine to postmortem wandering. K. inermis coronellae in these snakes is a normal inhabitant of the small intestine, but may wander occasionally into the stomach or lower esophagus. This movement may possibly be increased during or following postmortem changes. Individual Oochoristica osheroffi were generally attached to the duodenal mucosa; but in the undernourished snakes or in those that had not been fed for 2 to 3 weeks, they were sometimes found in the lower portion of the intestine. The total length of 0. osheroffi ranged from 5 to 396 mm. In the original description by Meggitt (1934) the range was stated as 60 to 205 mm. The highest rate of infection for any helminth was 72% for 0. osheroffi from the Keenesburg locality (Table I). Physaloptera sp. was next with a rate of 59% at both the Keenesburg and Platteville locations.