Mole Salamander

Because, like moles, they live almost entirely underground and are seldom seen. Adult mole salamanders occupy burrows, either digging their own in soft soil and leaf litter or moving into tunnels made by shrews, voles, and other small mammals, and they can be a metre or more below the surface. They spend the great majority of the year down there, feeding on soil invertebrates and staying moist and safe from predators and frost. They come to the surface only to migrate to breeding ponds, and even then they travel on dark, rainy nights, so a person could live for years beside a healthy population and never encounter one.

Yes. The axolotl, Ambystoma mexicanum, is a member of the mole salamander family, Ambystomatidae, native to the lake and canal system around Mexico City. What makes it unusual is that it does not undergo the metamorphosis that transforms other mole salamanders from aquatic, gilled larvae into land-living adults. Instead it keeps its external gills, finned tail, and larval body for its whole life while still becoming sexually mature, a condition called neoteny or paedomorphosis. Several other mole salamanders, including some tiger salamander populations in cold or arid regions, do the same facultatively. The axolotl is abundant in labs and aquariums but Critically Endangered in the wild.

For most of the year the salamanders are scattered underground and inactive. Then a specific trigger, usually the first prolonged warm rain after winter, sets almost the entire adult population moving on the same night or two. They walk, sometimes hundreds of metres, to a traditional breeding pond, one that dries out in summer and so holds no fish to eat the eggs and larvae. There, over just a few nights, males deposit sperm packets and perform nudging courtship, females pick up the packets and lay egg masses on submerged sticks, and then the adults leave and return underground. Concentrating breeding into a brief window swamps predators and makes sure the sexes meet.

The loss of small, temporary, fishless ponds. Mole salamanders are tied to woodland pools that fill in winter and dry in summer, because the drying kills fish that would otherwise eat their eggs and larvae. These pools are easy to overlook and are routinely drained, filled, or bulldozed for farming and building, or they are deepened and stocked with fish. Even where a pond survives, a new road between it and the surrounding forest can kill most of the migrating adults under traffic on breeding nights. Because the animals are long-lived, slow to mature, and faithful to one pond, a population can wink out quietly after its pool or its migration route is lost.