Saturday, March 22, 2014

The Venomous Snakes of Illinois

     People often erroneously refer to snakes as “poisonous,” but the proper technical term is venomous. The difference is that poison is ingested and venom is injected. If the toxin is from eating or touching the organism, then it is poison. If the toxin is from a bite by an animal, then it is venom.
     The Timber Rattlesnake (Crotalus horridus) is one of four species of venomous snakes in Illinois. The name “crotalus” comes from the Greek “krotalon” and means “a rattle,” while “horridus” means “dreadful.” However, these beautiful creatures are not to be feared and people are usually surprised to learn that they are actually very docile animals. They rarely need to strike since they can warn any perceived threats by shaking their rattles.

     A rattlesnake adds a new segment to its rattle every time it sheds. The rattle is completely hollow and there is nothing inside; rather the rattling sound comes from the ends of the rattle segments hitting one another when the snake moves it tail rapidly.
Some snakes have weak tail muscles and are unable to move their tails fast enough to make a rattle sound. This seemingly deleterious condition is actually advantageous in the human dominated landscape, and is a great example of evolution at play.
     If someone wants to find a rattlesnake and kill it or remove it from nature, it is a lot easier if they are given an audible clue, as rattlesnakes are very cryptic and secretive and can be difficult to locate in the wild. People who love to kill snakes are perhaps outrivaled only by those who want to collect them for the pet trade. In some places still, people have events in which the purpose is to find and kill as many rattlesnakes as possible.
     Rattlesnakes that cannot produce an audible rattle when threatened are not heard and therefore not found and killed. In South Dakota for example, this is leading to populations in which the majority of the rattlesnakes cannot rattle. The environment has selected the favorable trait, for better or for worse. The media would like to suggest it is for worse, claiming the snakes are now silent killers and should be feared. But conservationists hope this allows the species to rebound, and although the long term effects of this are largely unknown, it is a case of evolutionary biology in progress.
     Cottonmouths (Agkistrodon piscivorous) are very restricted in Illinois and only occur near large wetlands, mostly in Jackson, Johnson, and Union counties in southern Illinois. “Agkistrodon” means “hooked tooth” and “piscivorous” means “fish-eater.” These snakes are also sometimes called water moccasins, but that is a misleading name. People often use it whenever they see a snake in the water. However, all snakes swim and there are 5 different species of watersnakes (Nerodia sp.) in Illinois which can look similar and are much more likely to be encountered.

     One place where cottonmouths can be seen in abundance is at LaRue Pine Hills Ecological Area in Union County, Illinois. On any given day in the spring and fall, many can be seen crossing the gravel path, known as the “snake road.” Called the annual snake migration, many animals, not just snakes, move from the steep upland woods across the gravel road to the vast floodplain swamp. Due to the local tradition of driving this road to run over snakes, the road is now closed for two months in the spring and fall to allow for this fascinating wonder of nature. In fact, 65% of the reptiles and amphibians that occur in Illinois can be found at this single 2811-acre site. All collecting is prohibited.
     Cottonmouths have very whitish mouths that they like to open as a defense posture. Some people claim to have been charged by this species of snake and this perceived aggression has led to the unfortunate phrase, “the only good snake is a dead snake.” In my experience, if you leave a snake alone, it will leave you alone. There is a reason why the vast majority of snake bites involve these things; young men, alcohol, and getting bitten on the hand.

     In actuality, every organism has its place in the food chain, every organism has inherent biological value, and every organism has the right to exist and prosper. However, humans tend to play favorites and snakes are rarely on the list, although they should be, mostly because they are excellent at rodent control.
So be kind to snakes, even the venomous ones.

     Although seldom seen, the most common of the four venomous snakes in Illinois is the copperhead (Agkistrodon contortrix). Despite being morphologically variable, their cryptic appearance allows them to hide extremely well. In fact, one time while in the company of Southern Illinois University Zoology professor Matt Whiles, he pointed to an area in the front of his yard, and mentioned that he had seen copperheads there in the leaves. We looked closer and then spotted a copperhead hiding in the leaves.
     Another time while leading a group in nature, I noticed a juvenile copperhead coiled up among the base of a cliff after most of the group has walked right by it. Funny story, at the same time exactly one week later, I told another group about seeing a copperhead in that spot the week before and when we got there, the snake was in the exact same place!

     “Agkistrodon” means “hooked tooth” and “contortrix” means “twisted” or “intricate”, referring to the dorsal pattern on this species. It is very useful to notice this pattern in order to distinguish this species from watersnakes, such as the northern watersnake (Nerodia sipedon). Notice that the dark portions of the bands are shaped like an hourglass, or Hersey’s kisses, whereas on the watersnake, the pattern is the opposite. Of course there are other more subtle differences. All venomous snakes have elliptical pupils and nonvenomous snakes have round pupils. Venomous snakes also have triangular heads and although this may seem like a minor feature, once you observe a lot of snakes, this becomes readily apparent. Notice whether the head is the same size to slightly larger than the body of the snake, or if the base of the head is noticeably larger than the body of the snake.

     One of the situations in which copperheads are frequently found is in the wood pile in rural areas. They are a social species and are known to hibernate with other venomous snakes like timber rattlesnakes, as well as nonvenomous snakes, such as black rat snakes. Their bite is rarely fatal and most individuals are bitten while attempting to kill the snake. It’s best to just leave them alone.

     The last venomous snake in Illinois to be presented on this page is the rarest of the four. The eastern massasauga (Sistrurus catenatus) is type of rattlesnake native to the once expansive prairie of Illinois. Most of this prairie was wet prairie and it has been converted to agriculture. Now most of the massasaugas are gone. However, scattered populations can still be found in extreme northern Illinois and as far south as Clinton County. They are listed as state endangered in Illinois and are a candidate for federal listing.
     “Sistrurus” comes from two Latin words which translate to "rattle tail.” The epithet “catenatus” means “chained”, describing the dorsal pattern. The word "massasauga" is believed to mean “great river mouth” in the Chippewa language and it refers to swampy habitats found near the mouth of rivers in which these snakes can be found. Also called prairie rattlesnakes, this species spends a lot of time utilizing burrows created by crayfish. They come out of the ground in spring, covered in mud, and bask in the grass on warm sunny days, like the individual in the photo.