It's mid-March and the frogs are beginning to stir. As I write this I can hear the scrape of snow shovels on my neighbors' sidewalks. Last night it got cold enough to freeze a frog so solid you could use it as a paperweight, but despite the wintry weather this is the time of year when frogs come out to play. They announce spring to me when I visit the Somme Woods Forest Preserve very early in the morning at this time of year. The pond next to the lot supports what sounds like a healthy population of chorus frogs. The males make a noise that is usually described as similar to the sound you produce by scraping your thumbnail across the teeth of a comb. Get enough frogs and the sound becomes continuous and seemingiy sourceless, pouring out of the pond like an emanation of springtime.
Like rock and roll, the music of frogs is mainly about sex. The males are trying to attract females. In the case of chorus frogs, the females seem to be attracted not just to the most musical individuals but to ponds where the volume of the chorus is especially high. The value of that behavioral response is easy to see. The best ponds support the most males, and it is advantageous to a female to lay her eggs in a good pond.
She lays her eggs in a masss in the water, and they hatch into tadpoles that metamorphose into adult frogs. The whole cycle may be completed by the middle of June, which is fortunate, because the pond at Somme usually dries up by then. The frogs move away from the dried-up pond into wet prairies or sedge meadows, where you can sometimes see them hopping about after summer thundershowers.
The sound of the frogs set me wondering about what other herpetiles might be lurking in the weeds and waters at Somme. Herpetiles--or simply "herps"--is the general term used to describe amphibians and reptiles. The word is Greek and means "creeping."
Aside from the sound of those chorus frogs, my only other herpetological observation at Somme was of a smooth green snake that had recently been sent to its eternal reward by a grackle. But Somme Woods is one of the sites along the North Branch of the Chicago River that is being restored by the North Branch Prairie Project. As such, it is rapidly becoming one of the most studied pieces of ground in North America.
So I was reasonably sure that somebody must have surveyed the herps there. And indeed, Tom Anton of the Field Museum has done exactly that. His survey reveals known locations for reptiles and along both the North Branch and the Des Plaines River.
The list of species is rather short. The whole region covered by the report contains two species of salamanders, one toad, four frogs, four turtles, and six snakes. Another list of unconfirmed but possible species includes one salamander, two frogs, three turtles, and four snakes. These possible species are known to occur around Chicago but have not been documented in the study area.
Not all the documented species have been seen at Somme. We have only one species of salamander, the blue-spotted, which belongs to a family called mole salamanders. As the name suggests, they spend most of their lives underground, which makes them very difficult to see.
If you wanted to see one, you could go out at night during this time of year and wade in some icy pond with a dip net. They congregate in ponds to breed, but they do that very quickly. One night may be enough time to complete courtship, copulation, and egg laying, and then they go back to their subterranean ways.
The biggest blue-spotted ever captured was six and a quarter inches long, and many adults may be no more than four inches long, so they are easily overlooked even when they come out in the open. They eat earthworms and other soil-dwelling creatures.
We also have American toads at Somme. Toads are mostly terrestrial creatures, but they do have to go to ponds to breed in the spring.
Bullfrogs--the largest of our frogs--and the very similar green frogs are found along the North Branch, but not at Somme. At Somme the river has been channelized, converted from a naturally meandering stream into a straight ditch. The high, steep banks of the ditch make it pretty well impossible for frogs to get in and out of the water, so aquatic species like bullfrogs and green frogs cannot live there.
Channelization, which has been going on for decades under the auspices of the Army Corps of engineers, the U.S. Soil Conservation Service, and other agencies, is one of the worst river management ideas ever conceived. The justification for it is flood control. The ditch controls floods by moving excess water more rapidly than a natural river would. Of course we can't really control floods, we can only move them. Channelization moves floods downstream where the rivers are larger and human populations are bigger and the floods can really do some damage.
If the river had been left alone, it would meander through the forest preserve--the old channel can still be traced--producing habitat for bullfrogs, green frogs, and lots of other creatures as well. Periodic flooding would favor plants adapted to life on a floodplain and foster the growth of a floodplain community that would increase the biological diversity of the preserve. Every time I look at the ugly gash of that ditch I start daydreaming about what could be done with a bulldozer and a few well-placed sticks of dynamite.
The snakes of Somme are all small, inoffensive creatures. The smooth green snake is a true prairie species in this part of its range, and it has suffered greatly from the destruction of the Illinois prairies. It is a beautiful little snake. Its bright green coloration is almost iridescent.
The midland brown snake is even smaller than the smooth green snake. The record specimen is only 18 inches long. It is a good city snake, able to thrive in parks, cemeteries, and other small patches of green in urban areas. In natural conditions it favors moist situations such as wet woods or the borders of marshes.
We have two species of garter snakes at Somme. Garter snakes are all members of the genus Thamnophis, a highly successful group with about a dozen species in North America. One of our species is the eastern garter snake, Thamnophis sirtalis, and here in Chicago we have a distinctive subspecies, T. sirtalis semifasciatus, that carries the common name of Chicago garter snake. Maybe we should ask the City Council to name this the official municipal snake, although, come to think of it, there are a lot of aldermen with equally strong credentials.
Our other garter snake is the plains garter snake. The eastern garter snake's range extends to just west of the Mississippi, while the continuous range of the plains garter extends into western Indiana, so we are located in the relatively small region where the two overlap. In general, the plains garter snake is associated with wet prairies and the eastern with more wooded situations.
The red-bellied snake is the smallest of the Somme Woods species. Common size is just 8 to 10 inches long, and the biggest ever discovered was just 16 inches long. This is another snake that likes wet areas. The only ones I have ever seen were in sphagnum bogs in northern Wisconsin.
Garter snakes get big enough to catch and eat small frogs, but for the most part all of these snakes eat insects, spiders, and other small invertebrates.
The only turtle reported from Somme was a common snapping turtle. These highly adaptable reptiles are found in lots of places, but the channelizing of the river makes things difficult even for them. The river is also affected by creosote leaching out of ties on the railroad that parallels the stream through most of the Somme preserve.
All these herps are inconspicuous. Except for the singing of the frogs in spring, you could spend weeks at Somme and never see one. But they all play a role in the ecosystem, and they have all been hit by pesticides, and habitat fragmentation and all the other indignities we have visited on the natural world in this century. The list of possible but unconfirmed species I mentioned suggests that we may already have lost a number of herpetiles from Somme. What we see there now may be only a remnant, the surviving fragment of what was once a much richer community.