Scientific Name: Ambystoma maculatum
Common Name: The Spotted Salamander
(Information for this species page was compiled in part by Brittany Wetzel for Biology 220W, Spring 2006, at Penn State New Kensington)
The spotted salamander (Ambystoma maculatum) is a large (adults are, on average, 6 to 7 inches long with some individuals reaching 9 inches), distinctively colored (dark gray or blue-black on its back with two, full body length rows of round, orange or yellow spots) salamander found on our Nature Trail. This salamander, though, is seldom seen by students or hikers on the trail since it spends almost all of its time burrowed into the soil or hiding under rocks, logs, or wet leaf litter. Ambystoma maculatum, because of this tendency to live underground is often, along with several other relate species, referred to as a “mole salamander.” Only on rainy nights especially in the early spring is this beautiful amphibian reliably seen up and wandering across its forest floor habitat.
The spotted salamander is found in suitable habitats throughout the eastern part of the United States north of Florida. Suitable habitats must have two appropriate sub-habitats: vernal (“spring”) pools and ponds for the egg and larva stages, and moist forests (typically mixed hardwood forests) for the terrestrial juvenile and adult life forms. The vernal pools are a particularly critical and highly vulnerable component of A. maculatum’s habitat. These pools form in the early spring from snow melt and/or rain runoff. They must be shallow, isolated, and seasonally transient so that fish species do not become established in them. Fish prey heavily on the eggs and larvae of A. maculatum and, if present, would cause the failure of the salamander’s reproductive event. These pools, though, must have a sufficient water to insure that they do not completely dry out before the salamander larvae have had sufficient time to develop into their initial terrestrial forms. It is also important the these pools form reliably year after year since the adult spotted salamanders return to the same pool to breed in which it had developed as a larvae.
Vernal pools are subject to human disruption and destruction through the modification of natural drainage and runoff patterns. They are also very vulnerable to pollution from runoff or melt water (road pollution (salts and heavy metals like cadmium and lead) are especially common and frequently toxic sources of contamination). Further, these accumulated pollutants rise in concentration in the transient pools as the water slowly evaporates over the spring and summer seasons. Acid rain and the presence of air-borne pollutants also can profoundly affect the water quality of these transient, vernal pools.
The habitat demands of the terrestrial life forms of A. maculatum are not as stringent as those of the egg and larval life stages. Almost any forested habitat either with overall or microhabitatively occurring regions of high soil moisture and the presence of substantial cover (logs, rocks, leaf litter etc) will suffice for the needs of A. maculatum. Riparian forests, bottomlands, upland forests, and even montane forests may, if they have sufficiently moist refugia, support populations. Ideally, these sites would also have cool summer temperatures and non-freezing winter temperatures (at least in the salamander’s microhabitats).
Adult salamanders migrate between their terrestrial habitats and their breeding pools in the early spring. Warm, wet conditions favor this event, and overcast nights during snow melt or during spring rains are prime times for this breeding migration. The salamanders may travel several hundred yards relying on chemical cues for direction and are, as mentioned previously, “faithful” to their original breeding pools.
Breeding may last for up to a week with males clinging onto females and releasing their packets of sperm (“spermatophores”) which are then picked up by the females prior to egg laying. Females produce distinctive clumps of eggs usually in clusters that are four inches across. They attach these clusters to underwater sticks and to the stems of plants. These egg masses may be clear to white in color with many levels of color gradation in between. The color is generated by specific proteins in the egg mass’s jelly-like coating. This coating is thought to help protect the eggs from potential predators. The color of the coating seems to have an influence on the survival rate of the eggs. Clear coated eggs masses have a higher survivorship and hatching success than white coated egg masses. Also, there is often a symbiotic algae (Oophala amblystomatis) in the jelly coating. These algae increase the oxygen supply to the developing A.maculatum embryos.
Development of Young
The eggs hatch in two to four weeks (often in mid-May). The half-inch long larvae look like tadpoles and have prominent feathery gills on their heads. The larvae are a dark, olive green on their backs and a somewhat lighter color on their bellies. The larvae eat zooplankta and insect larvae and, in times of low food availability, each other. The larvae are, in turn, preyed upon by crayfish, frogs (both adults and tadpoles), fish (if they have not been excluded from the vernal pool), snakes (especially young northern water snakes (personal observation)), birds, predaceous aquatic insects, turtles, and, sometimes, even other salamanders. The survival rate of A. maculatum larvae is very low. After two to four months of growth and development, surviving larvae metamorphose into terrestrial juvenile forms. These juvenile salamanders are a few inches long and will, if they survive the stresses and predation pressures of their terrestrial habitats take two to five years to grow into reproductively mature adults.
Diet and Predation
The terrestrial juvenile and adult A. maculatum eat a great variety of invertebrate food sources including earthworms, snails, slugs, spiders, millipedes, centipedes, isopods, and insects. Anything that an individual A. maculatum can physically swallow is a potential prey item. Spotted salamanders are, in turn, preyed upon by chipmunks, snakes, squirrels, raccoons, skunks, turtles, and opossums. The preference of the salamanders for hidden microhabitats is their primary defense mechanism against predation. A milky toxin secreted from glands on the back of their tails also functions to repel and disgust predators.