Anecdotal reports that ecdysis in the Southeast Asian tropical viper Calloselasma rhodostoma occurs when humidity is high. Humidity may be important during ecdysis to prevent dehydration, a risk of the increased activity required for shedding and potentially increased rates of cutaneous water loss. However, little is known about the role of humidity in ecdysis cycles in natural populations of reptiles. We here report an aggregation of Eastern Ratsnakes (Pantherophis alleghaniensis, formerly Elaphe obsoleta) that exhibited synchronized ecdysis, apparently linked to humidity. The thermal ecology of P. alleghaniensis has been relatively well described, but there seems no existing information on the role of humidity in behavior, nor of synchronized ecdysis in wild populations. Bradley Carlson and colleagues made observations at Penn State University’s Russell E. Larson Agricultural Research Center at Rock Springs, Centre Co., Pennsylvania, suggesting humidity stimulates ecdysis in the Eastern Ratsnake. On May 13, the authors first noticed P. alleghaniensis in the rafters of an old barn located on the edge of the forest. Over the next 11 days, P. alleghaniensis were observed in the barn on most days, appearing to be absent only during particularly hot or cool weather. As many as six P. alleghaniensis were observed at one time. They were usually motionless, coiled up, or stretched along a beam. Many of the snakes, exhibited cloudy, bluish eyes and/or dull body coloration, indicative of the onset of ecdysis. On 29 May, shed skins (but no snakes) were found in the barn, and no recent skins had been found before this date. The authors collected the skins determined they were from at least four individuals based on the number of heads represented and the total length of the skins. No other snake species besides P. alleghaniensis occur at this location consistent with the size and scalation on the shed skins. An examination of weather records from the nearest weather station indicated that this large number of shed skins appeared after a day characterized by a high peak in humidity and a significant rain event during the observation period. This was preceded about one week earlier by elevated humidity and rainfall as well. This strengthens previous suggestions of synchronized shedding in wild snakes. Furthermore, it suggests that these ratsnakes took refuge at the same (and potentially environmentally favorable) site for ecdysis until some environmental factor may have triggered ecdysis. The most probable cause appears to be favorable levels of humidity coupled with rainfall, which may have been potentiated by an earlier period (19–23 May) of elevated humidity and rain. The authors could not rule out other environmental factors or that shedding occurred at certain period after the snakes emerged from a hibernacula or in preparation for egg laying.
Carlson, B. E., Williams, J., & Langshaw, J. 2014. Is synchronized ecdysis in wild ratsnakes (Pantherophis alleghaniensis) linked to humidity? Herpetology Notes, SEH 7: 471-473