Exploring a Vernal Pool
By Arianna & Frank Grindrod
Spring is in the air; in the yellow spotted salamander’s feet marching across the snow; in the trill of the Spring Peeper announcing his space and his availability as a mate; and the quiet patience of the Fairy Shrimp waiting between the mud and ice for their home to thaw.
What Is a Vernal Pool?
A vernal pool is a small woodland wetland that is created by melting snow in an earthen depression which has no inlet or outlet; basically a “wicked big puddle”. These “puddles” are nurseries for several species including mole salamanders such as the yellow-spotted salamander, wood frogs, spring peepers, fairy shrimp, and fingernail clams. Vernal pools are usually temporary and dry up as the season progresses. For the animals who them as a nursery, it is essentially a race against time for the babies to grow up enough to be out the pool before the water is gone. Some pools are semi-permanent but that is not a guarantee so ether way, the salamanders and frogs are crawling or hopping away come summer. The invertebrates, those who cannot fly or crawl away, but are obligate to the pools such as the fingernail clams and fairy shrimp must squiggle down into the mud and wait until next spring to emerge again.
Who Might you Meet at a Vernal Pool?
Mole salamanders live underground which is why you don’t tend to see them any other time of year…except for the Marbled Salamander who lays her eggs in the fall in autumnal/vernal pools. She hoovers over her eggs until the rains fall and then she leaves them. These little ones are the first to hatch and will eat other species of mole salamander eggs in the spring when the pool has then been filled with Jefferson, Yellow-Spotted and Blue-Spotted Salamander eggs. All mole salamander species eat invertebrates and will use mole-excavated tunnels, hence why they are called mole salamanders. In the Spring, when the first rains tickle the ground and when above ground temperature reach 40 degrees Fahrenheit, the Yellow-Spotted, Blue-Spotted, and Jefferson all come on down to their home pools. The males arrive first, forming what is called “congress”, a group of salamanders. They may travel up to a half mile away from their upland forest underground homes to mate in these vernal pools. After they mate they return to their woodland homes. Watch for them on rainy spring evenings as they cross the road.
If you live near a vernal pool you may hear a din of sound that is caused by two vernal pool visitors – the Wood Frog and the Spring Peeper. The Wood Frog is one of our black-masked bandits (can you guess the other two? One is a mammal and the other is bird.); a woodland, territorial amphibian that has a very distinctive call – the singing males, who are calling out to alert everyone in the vicinity that this is their space make a “qua-ack” sound, vaguely reminiscent of duck. The Spring Peeper is a very tiny tree frog who bears an “X” on his/her back. The callings males make a high-pitched “ree-deep” sound.
There are a host of invertebrates that you can find in a vernal pool – from Predaceous Diving Beetles and Whirligig Beetles to Damselflies to Backswimmers and Water Boatmen to Mayflies to Amphipods, Isopods, Daphnia and Copepods to Fairy Shrimp to Fingernail Clams to Caddisfly larvae. These are species worth getting down and dirty with as each sport their own unique adaptations of locomotion, feeding and general survival. For example, Whirligigs have split eyes so they can see up and down at the same time; handy when watching for predators. Mayflies have fanlike gills on their abdomen to take in oxygen from the water. Predaceous Diving Beetles have their own scuba gear so to speak; they carry an air bubble at the base of their abdomen as they swim through the water. Caddisfly larvae make their mobile homes from debris they find in the pool and their silk. They have a little hook on the end of their abdomen so they really do hitch up to their home and crawl along the bottom of the pool. They keeps their soft bodies protected and camouflaged.
Exploring a Vernal Pool
You and your youngster can gently explore these nurseries using a simple dip net and a holding pan. Fill the pan with water from the pool being careful to obtain the clearest water so that your temporary holding container is not muddy. Now gently slide your net through the pool and along the edges to catch a critter. Gently put it in the pan using a plastic spoon. If you have a magnifying lens and an identification guide book so much the better. Watch how the creature moves. It is recommended not to place predators and prey species in the same holding container at the same time else you will be setting the stage for the prey to be on the losing side of the chase. Please also do NOT collect eggs as this action may destroy the embryos.
When you are through studying these amazing creatures please return them to their home in the pool. To emphasize to your young naturalist the importance of respecting wildlife you can end with a simple “repeat-after-me” releasing ceremony such as this one that I (Arianna) learned from Kim Noyes at Northfield Mountain Environmental and Recreation Center many years ago.
“Run away, crawl away, swim away, hop! You are free to go. I am not going to stop you from living your life. You deserve to be free; but thank you for spending this time with me.”
Suggested Field Guide: A Guide to the Animals of Vernal Pools by Leo Kenny & Matthew Burne.
Amphibians, including frogs, toads and salamanders, breathe through their skin. Their skin is very sensitive to many things (salt, chemical toxins, soap, bug repellant, chlorine in our drinking water, sunscreen, etc.) When handling our wild friends, please remember to create a micro-habitat between you and them. Create this layer by putting your hands in their water source (vernal pool, pond, bog, stream, etc.) if they are aquatic or by using soil and leaves if they are terrestrial. When holding an amphibian make sure you keep them low to the ground and be mindful that the temperature of your hands can raise theirs, and this can create stress for them. Always return them where you found them. Or, if you are helping them cross a road, always remember their direction of travel and place them on the proper side of the road according to their direction of travel.