Life Histories of Some Common Vernal Pool Organisms
Wood Frog * Spotted Salamander * Fairy Shrimp
Spring Peeper * Green Frog * Water Beetle * Fingernail Clam
Wood Frog (Rana sylvatica)
Wood frogs are common inhabitants of vernal pools in the Deerfield River watershed. They range from 2-3 inches in length, and vary in color from dark brown to tan to shades of pink. Males are usually darker in color than females. Both sexes have a dark mask running through and beyond their eye. The best time to observe wood frogs is in early spring when they return to vernal pools to breed. In the watershed, choruses of males have been heard from late March to late April. Listen for wood frogs on rainy nights in early spring when the snow has begun to melt.
Additional natural history facts:
- Breeding calls sound like quacking ducks
- Females typically lay their eggs in large rafts in the warmer sections of the pool
- Each small black egg is surrounded by a jelly-like matrix and each egg mass may contain between 500 and 1,500 eggs
- Egg masses are about the size of a tennis ball or larger
- Wood frogs may remain in their breeding pools for as long as several weeks
- Eggs hatch in approximately 3 weeks and newly-hatched tadpoles stay close to the spent egg masses
- Most young wood frogs leave their breeding pool in about 70 days
- Wood frogs are habitat generalists and can be found in wooded habitats, meadows, riparian areas, and the edges of marshes and bogs.
- Food of adults: small insects (crickets, beetles, caterpillars), spiders, earthworms, and slugs.
- Wood frogs overwinter under the leaf litter, in tree roots, or shallow burrows, and in rotting logs and stumps.
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Wood frog egg masses clustered in one section of pool
The green color is from an alga that colonizes the egg masses. The alga does not harm the eggs
Spotted Salamander (Ambystoma maculatum)
This salamander is large and chunky, ranging from 4.5 and 9.0 inches long. Its bright yellow spots scattered on a black to dark gray background make it easy to identify. Spotted salamanders are rarely seen outside the breeding season, which takes place in late winter or early spring when adults leave their underground burrows and travel to vernal pools. During studies in the Deerfield River watershed, adults were rarely observed in pools.
Additional natural history facts:
- Breeding takes place when night time temperatures reach about 40 degrees F and rain has occurred during the day or evening
- Salamanders tend to use same pools every year to breed
- Adults stay at pools for several days to weeks
- Egg masses are usually attached to small twigs or other vegetation in the pool
- Each egg mass contains from 30-250 individual eggs surrounded by a firm, gelatinous covering; masses may be quite small (an inch or two) or up to 6.0 inches
- Egg masses turn green in color from a symbiotic algae
- Hatch occurs between six and eight weeks after eggs are laid
- Larvae can be distinguished from frog tadpoles by the presence of feather-like gills
- Young salamanders leave pools when about 2-3 inches long and after approximately 70-100 days
- Habitats: deciduous or mixed deciduous forests and conifer forests
- Food of adults: worms, slugs, snails, beetles, ants, spiders, centipedes, crickets
- Spotted salamanders are nocturnal and spend their time under logs and leaf litter and in small mammal burrows
- Overwinter in small mammal burrows
Adult spotted salamanders found crossing road in spring in western Massachusetts
Spotted salamander egg mass: note that each egg mass is surrounded by a jelly-like matrix
Young spotted salamander larva
Note the feather-like gills around the head which distinguishes it from wood frog tadpoles
Spotted salamander larva about 1.5 inches long
It is about 60 days old and will be ready to leave pool between 70-100 days after hatching
Fairy Shrimp (Genus Eubranchipus spp.)
Fairy shrimp are small crustaceans (0.5-1.5 inches long) that require fishless pools to breed successfully. In early spring they can be found floating on or near the surface and look superficially like small green or orange shrimp. The fairy shrimp found in our area belong to the genus Eubranchipus. Fairy shrimp hatch from eggs that lie on the pool bottom until the pool fills with water. They feed while laying or swimming on their backs, filtering various small microorganisms, algae, and bacteria. Fairy shrimp are found in pools in late winter and early spring, before water temperatures reach between 68 and 72 degrees F. It is likely that fairy shrimp have evolved to complete their life cycle before most predators become active in the pool. Their distribution at pools is not predictable and they may be observed in some pools every year, or be found sporadically in others.
The Vernal Pool Association website has wonderful photographs of a variety of invertebrates, including fairy shrimp. Go to their image gallery to see photographs of many vernal pool organisms: http://www.vernalpool.org/BSW/index.htm.
Other animals that may be found in vernal pools but are not dependent on them to breed successfully:
Spring Peeper (Pseudacris crucifer)
Spring peepers are familiar to most people because of their loud, deafening, high-pitched choruses heard during spring throughout New England. They are small frogs, about an inch long, with a dark X on their back. The color of adults ranges from light to dark brown; some individuals may be reddish in color. Although peepers will breed in vernal pools, they prefer those that hold water for longer periods, at least 9 months. Peepers have an extended breeding season and may remain at pools from March to May. These frogs may be heard calling during the fall in woodlands throughout the Deerfield River watershed.
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Adult spring peeper observed crossing the road in western Massachusetts
Green Frog (Rana clamitans)
Green frogs are one of the watershed’s most common frogs and are found in a variety of wetlands, from rivers and streams to vernal pools and marshes. Their color is variable, primarily green but also brown, with spots on their legs. Green frogs are large – from 2.5 to 4.0 inches long. Their call sounds like the twang of a guitar string. Green frogs are usually found in vernal pools that hold water throughout the summer or that are semipermanent (e.g., hold water year- long most years). These frogs prey upon flies, beetles, grasshoppers, spiders, and other frogs.
Adult green frog: distinguished from the bullfrog by the two ridges that run along its back
Water Beetles (Order Coleoptera)
This large and diverse group of beetles is an important component of the vernal pool community. Adults and larvae from many families may be found in pools.
- Beetles vary in size, coloring, and life history traits; adults can be quite small (less than 0.04 inches) or very large (over 2 inches)
- Beetles exhibit diverse feeding strategies, depending on the species and life stage (larva or adult)
- Carnivorous species prey upon crustaceans, worms, salamander larvae, frog tadpoles, and other insects; other species are omnivorous or feed on algae and decaying vegetation
- The number of water beetle species found in vernal pools generally increases with the length of time that the pool holds water
- Some water beetles remain in or near vernal pools for their entire life (e.g., egg to larva to pupa to adult); others may use the pool for feeding only, and some breed in the pool but overwinter in permanent water bodies
Adult water beetle
Fingernail Clams (Phylum Mollusca, Class Bivalvia)
Fingernail clams are small bivalves with a shell length of less than 0.5 inches. Depending on the species, shell color ranges from off-white to light brown, or shades of gray. Several species may be found in vernal pools.
- Fingernail clams are found scattered within and on top of the leaf litter at the bottom of pools
- Clams bear their young alive and they look like miniature adults
- Clams are filter feeders; they eat microscopic animals, algae, bacteria, and dissolved organic material by straining small particles with their gills
- Dry periods are survived by burrowing into the mud and leaves on pool bottom
- Clams spend their entire life in the vernal pool and, depending on the species, may live up to three years
See a fingernail clam photo