Marbled Salamander (Ambystoma opacum)
This is a chunky bodied, black or dark brown salamander with bold white or gray markings on the head, back, and tail. The light, silvery markings form cross-bands that run the length of the back and may merge into a stripe on each side. Adults are 3.5 to 5 inches (9 to 12.7 cm) long.
Photo © Jim Harding
Just about the time most other amphibians are looking for places to winter hibernate, marbled salamanders are heading to breeding areas. The only fall breeding salamander, they seek out small areas (micro habitats) with temperatures around 60°F. The female will lay an average of 100 eggs in a nest constructed in a shallow depression under leaf litter or in a log. The female remains with the eggs until fall rains fill the nest site. Eggs will hatch within two weeks. In mild winters, larvae can feed and grow and transform in late spring or early summer. If the nest site does not flood, eggs will go dormant until the following spring. The salamander larvae that do not hatch in fall metamorphose into terrestrial adults in late spring or June or July.
Uniquely, Marbled Salamanders breed in fall instead of spring. Females lay eggs in depressions under leaf litter or logs, in low spots that fill with fall rains.
The habitat they select varies with the season. During the spring and summer, the adults spend their time in sandy upland deciduous forests. They seek shelter under logs or in underground tunnels of other animals. Their diet consists of earthworms, insects, slugs, and other small invertebrates; the larvae often eat the larvae of other amphibians. In autumn, they congregate in groups near lowland forested habitat to breed.
The marbled salamander is a nocturnal, secretive creature that is rarely, if ever seen. The Michigan population is restricted to scattered populations in southwestern counties. It is more widely found in southeastern United States.
In Michigan, the marbled salamander is currently listed as threatened due primarily to habitat fragmentation, wetland drainage, channelization, and filling. It has not been reported in Michigan for many years, and may be extirpated. Since shallow woodland ponds often freeze completely during typical winters, it is likely that the fall breeding habits of this species are not well adapted to Michigan's present climate.
The survival of this species in Michigan will rely on identification and conservation of sites found to have marbled salamander populations. Since they migrate to their breeding areas, it will also be important to identify migration routes that may cross roadways. Recovery at these sites will require safe passage between forested uplands and lowland intermittent pools.
Report any Michigan sightings of this species to the DNR Wildlife Division.