A Closer Look
by Sean Green
Ribbon Snakes (Thamnophis sauritus )
Picture credits: Peninsula Ribbon Snake (Thamnophis sauritus sackeni) by Sean Green When I was a young boy I often came home with pet animals that I had found during hiking or camping trips, one of the most common being any species of garter snake (Thamnophis) that I could find. At first, the harmless snake was not welcome and I had to convince Mom that it would not get loose and even if it did, it was perfectly harmless. I cannot claim that my arguments ever set her mind at ease, but she did eventually develop a tolerance to my odd passions. These childhood memories arose again on a recent hiking trip through Circle B Bar Reserve off Lake Hancock in Polk County. The end of November was cool, I did not expect to see any snakes on my hiking trip, but was graced with seeing a Peninsula Ribbon Snake (Thamnophis sauritus sackeni) feeding on a frog. A closer look at this species will reveal why it may be one of the few snakes still active in Florida’s sparse bouts of cooler weather. What we commonly call “Garter Snakes” are small snakes in the (Thamnophis) genus. These harmless snakes are native to North America and are very common throughout the continent, including parts of Canada and Central America. Within the Thamnophis genus (basic garter snakes) is a species described as “Ribbon Snakes” (Thamnophis sauritus ). There are four recognized varieties called “subspecies” by scientists. The subspecies we are most likely to find in Hillsborough, Polk, and Heartland regions of Florida are the Eastern Ribbon Snake (Thamnophis sauritus sauritus ) and the Peninsula Ribbon Snake (Thamnophis sauritus sackenii). Members of the Thamnophis genus are among the most abundant snakes in North America. Averaging 30 inches in length, they can easily be housed and are a common first snake for budding naturalists that have a passion for reptiles. Although they are not venomous and rarely bite when handled, they do produce a foul musk from their anal gland when threatened and usually release their digestive track if danger persists. Ribbon snakes can be found in a variety of habitats including pinelands, hardwood hammocks prairies, marshes, streams, and ponds. Their main diet of frogs, fish and salamanders will direct their activity to water sources. Ribbon snakes are born in late summer and grow to maturity within a couple years. They typically remain active all year long, but do hibernate in ant mounds, or crawfish burrows when colder months make it necessary. The relationship between weather and Thamnophis birthing strategies has WWW.INTHEFIELDMAGAZINE.COM
been of particular interest to scientist and researchers Most reptiles are oviporous, they lay eggs that have a shell similar to that of a bird or platypus and from this external shell, the offspring emerges. Reptile shells however, are typically soft and leathery rather than hard and brittle like a bird egg but include a similar yolk that provides nutrition to the embryo while it develops. Most mammals are viviparous, they truly bear live young. There is no internal egg structure at any time during the development of the offspring. More importantly, a placental connection (rather than egg yolk) provides the embryo with nutrition during its development. There is a middle ground in birthing strategies, and the correct term for it is ovoviviparous, it describes animals that produce a shell and carry the eggs internally. The embryo is nourished with a yolk rather than a placental connection and completes its development while inside the mothers body. By the time the embryo has finished developing, the shell has worn to little more than a thin mucus membrane (like the inside membrane of a chicken egg). By the time the embryo is ready to emerge and the mother delivers the eggs, the shell is very thin, or already broken, making the delivery appear viviparous (live birth) when it is actually ovoviviporous, (an egg that was hatched within the body). Snakes can be either oviparous or ovoviviparous. Learning the snakes scientific name, such as (Thamnophis sauritus )will help identify the family the snake belongs to, in the case of our Ribbon Snakes (Thamnophis sauritus) a Google search will reveal it belongs in the colubridae family. Colubrids are generally egg laying (oviparous) snakes, in this case however, the garter snake genus (Thamnophis) is a fascinating exception. Scientist claim ancient reptiles switched back and forth between these two strategies around 175 million years ago to finally settle on egg-laying strategies (oviparous). The general consensus is that temperature was the dominant factor in the evolutionary strategy. Colder conditions increased the incubation time, requiring the female to retain the eggs longer and eventually triggered the switch to an ovoviviporous strategy. Should you happen upon a ribbon snake, or a garter in the cooler months when snakes should not be out, take notice, you’re witnessing an intelligent design that still astonishes scientists. INTHEFIELD MAGAZINE
December 2014
43