Nature Notes: Spotted Salamander
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by Ed Robinson
As March comes to Harpswell, a few things are certain: maple sap will be running on warm days, you can’t delay your taxes much longer and winter begins to lose its grip even if Mother Nature still has one more storm up her sleeve. As the days grow longer, and the snow gradually melts into low spots, you have the chance to witness one of life’s little miracles. One day when the temperature pushes toward 50 degrees with a good soaking rain, the spotted salamanders will emerge from winter hiding spots for their annual breeding migration.
This secretive amphibian is fossorial, meaning they spend most of their lives underground or hidden under downed trees. They favor hardwood forests with good water sources, and they emerge from their refuge on damp nights to forage, using a sticky tongue to catch insects, worms, slugs, centipedes and spiders. But a couple days of the year bring the right conditions for hundreds of salamanders to converge on vernal pools to breed and lay eggs. I have been fortunate to witness this event twice at our old farm in New York, and I was amazed at how many salamanders seemed to have appeared from nowhere.
The spotted salamander (Ambystoma maculatum) is a member of the mole salamander family. They have a broad flat head, with wide protruding eyes. The legs are thick, their tails are rounded and they have prominent vertical grooves along their sides. An adult can range from 6 to 10 inches in length. The main body color is black, but may show shades of dark blue, green, grey or brown depending upon genetics and habitat. The belly is grey and pink. What makes this salamander distinctive are the flashy spots on its sides and upper body, up to 50 of them ranging from bright yellow to orange.
Vernal pools are perfect habitat for the breeding cycle because the pools dry up in summer and thus do not support populations of predatory fish. Salamanders tend to breed in the same vernal pool every spring. The female lays about 100 eggs in a transparent jelly-like cluster, two to four inches long, that clings to underwater plants or rocks. But here is where things get interesting. The jelly protects the eggs, but it inhibits oxygen transport, which the embryo requires for development. In an unusual symbiotic relationship, the salamanders carry in their somatic cells a green alga, Oophila amblystomatis, which is passed to their eggs. During the 45 days of larva development, the alga photosynthesizes oxygen and the larva metabolizes the oxygen and produces carbon dioxide, which is consumed by the alga.
When the larva emerges, it is equipped with external gills that allow it to live underwater for the next 45 days of its life. During this time it consumes aquatic invertebrates, small crustaceans and insects. Soon the lungs are fully developed, and the larva undergoes the amazing process of metamorphosis. Its gills and fins disappear, the eyes develop lids, and the tail, skin and limbs become thicker to handle the remainder of its life on land. If the vernal pool dries up before metamorphosis is complete, the larvae will die.
These fascinating creatures have several methods of defense. First is their preference for remaining hidden underground or under logs and leaf litter. Second, the salamander is equipped with large poison glands on its back and neck, which excrete a milky toxic liquid when the animal is threatened. Finally, the salamander can shed its tail or limbs when attacked by a predator, with the ability to regenerate the missing body part in a few months. These combine to allow salamanders to live surprisingly long lives, up to 32 years in lab studies.
Scientists consider the spotted salamander to have a stable population. It ranges from Nova Scotia west to Lake Superior, and as far south as Texas. Salamanders, like other amphibians, are sensitive to changes in their ecology. They can be harmed by overuse of agricultural chemicals, increasing water acidity and the loss of upland and vernal pool habitat.
Efforts by conservation groups such as HHLT to preserve such habitats are clearly vital to ensuring that we will have plenty of these beautiful creatures to enjoy forever.