94 Charles R. Blem and Leann B. Blem 



Texas V. striatula ranged from 61-69 mm in snout- vent length (N = 8) 

 while the range of Virginia specimens was 73-79 mm (N = 7). Clark did 

 not calculate the percentage of mature females that produced young 

 each year, but we interpret his data as indicating that about 79% (30/38) 

 should have produced young. Clark and Fleet (1976) assumed that 

 mature females produced young once per year, but pointed out that in 

 some years this was not achieved. 



Blem (1981), in an analysis of the eastern cottonmouth at the 

 northern edge of its range in Virginia, found that a major limiting factor 

 was high overwinter mortality of young during very cold winters. 

 Reproductive rates were very high; 83% of mature females were gravid 

 during the breeding season (Blem 1982). The similarity of these findings 

 to those of the present study suggests that the spread of snakes north- 

 ward on the coastal plain of Virginia may sometimes be limited by the 

 balance between reproductive rate and cold-induced mortality. Further 

 comparison of our studies of Virginia and Agkistrodon, and a vast liter- 

 ature (e.g. Fitch 1970), suggest that some generalities may be recognized 

 regarding reproductive "strategies" of small colubrids and larger viper- 

 ids. In general, it appears that less than 100% of mature female viperid 

 snakes reproduce each year and the proportion is often nearer 50% 

 (Aldridge 1979; but see Kofron 1979 and Blem 1982 for exceptions). 

 Conversely, 90-100% of the females of many colubrid species, particu- 

 larly small snakes such as Carphophis amoenus, Diadophis punctatus 

 and Thamnophis sir talis, reproduce annually (Aldridge 1979). It there- 

 fore appears that one might expect a large proportion of the females of 

 a population of V. striatula to be involved in the production of young 

 each year. In many studies addressing reproductive output of snakes, a 

 relationship has been noted between litter size, or some other measure 

 of reproductive output, and female size (see Blem 1981, 1982). Both 

 small colubrids (e.g. Clark 1964) and viperids show this phenomenon. 

 However, frequency of reproduction appears to be a size-related phe- 

 nomenon in some viperids (Burkett 1966; Blem 1982), while that rela- 

 tionship has not been demonstrated for small colubrids. 



ACKNOWLEDGMENTS.— We are indebted to William Gutzke 

 for sharing one of his favorite collecting sites and for companionship in 

 the field. Several Virginia Commonwealth University herpetology classes 

 provided most of the manpower necessary for collecting specimens. 

 Cheryl Roeding, Gerald Schaefer and Tom Thorp also provided assist- 

 ance in the field. We also thank Carolyn Conway for assistance in 

 staining and staging embryos. 



