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.
Citation
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