Not all salamanders with red backs are equal. The eastern red-backed salamander, Plethodon cinereus comes up first when you search by color. It is found from Missouri's Bootheel all along the east coast and up into Canada. They are common forest dwellers, nibbling at invertebrates living in the detritus of decomposing vegetation. They are commonly found under rocks and logs and will even live in worm burrows. In a fertile environment there may be as many as 1,000 in an acre.
For such little guys, red-backed salamanders sure do get around. Amphibiaweb points out that 3/4 of their range was under the last continental ice sheet 21,000 years ago. This means that these little (less than 4" long) salamanders dispersed northward rapidly since then. Studies show that they are expanding their range by 80 meters a year, still moving north and likely will continue to do so with global warming.
We are west of the P. cinereus range and Brian Edmond straightened me out on our species, the Ozark zigzag salamander, Plethodon angusticlavius. It occurs in a very localized area of the southern Missouri Ozarks as well as down into northern Arkansas. We are located right in the middle of the Missouri territory. P. cinereus above was the original redback salamander before the other species were split off, scientifically more accurate but the bane of the beginning amateur naturalist.
Their coloration varies greatly, with two predominate forms the red-backed and the lead-backed which has no stripe down the back. While the red stripe might make them more vulnerable to predators, some authorities theorize it may also protect them by mimicking the red eft stage of the toxic red-spotted newt.
Plethadon species lack lungs and breath through their skin which must remain moist for them to absorb oxygen. They generally only come out of their moist covered habitat during a rain.
Unlike most salamanders, Plethodon species do not have an aquatic phase. Rather than lay their eggs in water, red-backs deposit them in clusters attached to the underside of rocks and logs while the zigzag lay eggs on the rock substrate and generally avoid logs. Ours apparently didn't get the message. Since the red-back female guards the eggs for six to nine weeks, she eats little during that time and remains smaller that males and non-breeding females. This probably accounts for why they usually breed every other year, the female needing the year off to store up nutrition for future egg yolks. Our zigzag breeds annually, possibly aided by the warmer climate with more feeding opportunities?
While the red-back is a creature of the forest, the zigzag prefers rocky terrain, especially glades. They especially migrate to glades for mating. Our wood pile is very near our glade, somewhat like having a great singles bar just down the street. No wonder we could detect a little smile on its face.
The larval stage is spent in the egg although there may be some remnants of gills when the young first hatch, a reminder of their distant ancestors life in water. The larvae and adults consume a variety of small arthropods and in turn are parasitized by some intestinal worms species and in one case chiggers!* Now that is something to watch for, a scratching salamander.
|Eastern Zigzag**- click to enlarge|
To my naive eye, the differences between species are subtle. Zigzags have an irregular strip zig and zagging down the back rather than the smooth straight sides of the red-back. There is also a northern (a.k.a. eastern) zigzag, Plethodon dorsalis dorsalis, which has a wider red stripe than the Ozark zigzags. One expert stated that nobody could tell them apart unless they knew where they were from first. These are minor color changes to us but studies show there are differences in genes and proteins as well. There also are significant behavioral differences between species in different environments. For instance, the northern species are less likely to find glades, changing their choices of cover and reproduction.
Over time the Ozark zigzag has managed to adapt to the climate changes of the Holocene, 11,700 B.P. to the present, surviving the early cool period as glaciers retreated from across the Missouri River to the north, through a warm and dry xerothermic period, the "little ice age" around 1300 A.D. to the present. Unable to go to Florida in the winter, they just holed up under rocks and waited a thousand years for a change in the weather.
* Zigzag parasites
** Photographs thanks to Serpent Ryan's Life List of Missouri Herps.
More on the Zigzag salamander at The Amphibians and Reptiles of Arkansas
More details on the Ozark zigzag salamander and the Eastern red-backed salamander
Caring for red-backed salamanders
Zigzag salamanders and landmark learning
For pictures of color variations of the red back, see fcps.edu.