Nature Notes: Spotted Salamander
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In late winter in Maine, a few things are certain: maple sap will be running on warm days, you soon have to complete your tax return, and winter is losing its grip even if there is one more storm in the forecast. As the days grow longer, and the snow gradually melts, 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, rocks and leaves. They favor hardwood forests with good water sources, and emerge from their secret spots on damp nights to forage, using a sticky tongue to catch insects, worms, slugs, centipedes and spiders. But a couple days each year bring the right conditions for hundreds of salamanders to converge on vernal pools to breed and lay eggs. Twice in recent years my timing has been just right, and I was amazed at how many salamanders converged to get in on the action.
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 reaches from six to ten inches in length. The main body color is black, but may have hints 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. There are nine recognized species of salamanders in Maine but it would be hard to find a more attractive one than the yellow spotted.
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 sticks 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 adult salamanders carry in their somatic cells a green alga, Oophila amblystomatis, which is passed to their eggs. During the 45 days of larval development, the alga photosynthesizes oxygen, 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 maturation. During this period, 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 enable the salamander to live 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 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. The ongoing decline in insect populations is also an issue for salamander diets. Efforts by conservation groups to preserve vital habitat help to ensure that the diminutive salamanders will prosper for a long time to come.