If the obligate species are using a body of water, then that water is a vernal pool. In New England, the easily recognizable obligate species are the fairy shrimp, the mole salamanders and the wood frog. Females eventually drop an egg case which remains on the pool bottom after the pool dries. The eggs pass through a cycle of drying and freezing, and then hatch another year when water returns. The presence of fairy shrimp indicates that a water body is a vernal pool.
Wood frogs are an amphibian species of upland forests.
They venture to vernal pools in early spring, lay their eggs, and return to the moist woodland for the remainder of the year. The tadpoles develop in the pool and eventually follow the adults to adjacent uplands. The mole salamanders are also upland organisms. They spend most of their lives in burrows on the forest floor. Annually, on certain rainy nights, they migrate to ancestral vernal pools to mate and lay their eggs.