Amphibians
Spotted Salamander
Ambystoma maculatum · also called yellow-spotted salamander
The spotted salamander is a large, glossy, black-and-yellow amphibian that most people who share the forest with it will never see. It lives underground almost year-round and reveals itself only for a few frantic nights each spring — and its eggs harbour one of the strangest partnerships in the animal kingdom.
Overview
Spotted salamanders live in moist deciduous and mixed forest across eastern North America, wherever there are fishless vernal pools for breeding. They belong to the mole salamander group, and the name is accurate: outside the breeding season they stay below ground, in burrows and root channels, hunting invertebrates in the soil and leaf litter at night after rain. An adult may use the same small patch of forest for its entire long life.
The spring migration
For a few nights each early spring — the first spells of warm rain after snowmelt — spotted salamanders emerge together and migrate to their breeding pools, often the exact pool where they hatched, along routes used for generations. Males arrive first and deposit stalked packets of sperm on the pool bottom; females follow, pick up a packet, and lay a firm, softball-sized mass of jellied eggs attached to a submerged twig. Within days the adults return underground.
Algae in the eggs — and the cells
The egg masses turn green, and for a long time this was known to be a symbiotic alga (Oophila amblystomatis) living in the jelly. The algae photosynthesise, raising the oxygen level around the embryos, which develop faster and hatch at a higher rate; in return they get nitrogen-rich waste and a protected, sunlit nursery.
In 2011, researchers discovered the algae go further, entering the salamander embryos’ tissues and even individual cells — the first known example of a photosynthetic organism living inside the cells of a vertebrate. How the developing salamander’s immune system tolerates this is still being studied.
Larvae and metamorphosis
The eggs hatch into gilled aquatic larvae that hunt zooplankton and other larvae in the pool. They must complete metamorphosis — absorbing the gills, developing lungs and stronger legs — before the pool dries, then leave the water and disappear into the forest floor, not to breed themselves for several years.
Status
The spotted salamander is Least Concern and remains common where its two habitat requirements are both met: intact forest and fishless seasonal ponds within migrating distance of each other. It declines when either is lost — when forest is cleared or fragmented by roads (road mortality on migration nights can be heavy), or when vernal pools are filled, drained, or stocked with fish. It is a widely used indicator of the health of forest–wetland systems.
Spotted Salamander: common questions
Why is the spotted salamander almost never seen?
It is a "mole salamander" — it spends the great majority of its life below ground, in the tunnels of shrews, voles, and moles and in natural spaces around tree roots, coming to the surface only on wet nights to feed and, once a year, to breed. An animal can live for decades in a patch of forest without a person ever noticing it. The best chance of seeing one is on the first rainy nights of spring, when large numbers cross roads and forest floor heading for their breeding pools.
What is "Big Night"?
The term naturalists use for the first warm, rainy night of early spring when spotted salamanders (and other amphibians) emerge en masse and migrate to their ancestral vernal pools to breed. Hundreds may move at once along traditional routes. Because these routes often cross roads, volunteers in many areas run "amphibian crossing" patrols on Big Night to carry salamanders and frogs safely across.
Is it true a salamander has algae inside its cells?
Yes — the spotted salamander is the only vertebrate known to have a photosynthetic partner living inside its own body cells. Green algae colonise the jelly of the eggs and boost the oxygen supply to the developing embryos, which grow faster and survive better as a result. Researchers later found the algae also penetrate the embryo's tissues and even individual cells, a genuine intracellular symbiosis of a kind thought impossible in animals with an immune system like a vertebrate's.
Why do spotted salamanders need fishless ponds?
They breed in vernal pools — woodland depressions that fill with snowmelt and spring rain and dry out by late summer. The drying is essential — it keeps fish out, and fish would eat the salamander larvae. The trade-off is a race against time, with the larvae needing to hatch, grow, and transform into land animals before the pool disappears. Ponds that are deepened or connected to streams, letting fish in, lose their salamanders.