Timeline of a Tadpole
By Jennifer Meikle, Environmental Educator
The month of May is a great time to check out what’s going on in your local pond or wetlands. This is the time of year when everything seems teeming with life and a perfect time to break out a scooping net to see what you can find! It’s likely you’ll find eggs or tadpoles in the water. There are a few different types of animals that lay eggs in ponds or vernal pools, and there are ways to distinguish one from another. If the eggs are circular, covered with a clear jelly-like substance, and laid in clusters those are probably frog eggs. If the eggs are laid in long, almost coiled chains, those are likely toad eggs. A mass of salamander eggs is more like one unified lump of jelly with the eggs inside. Newt eggs are laid individually on submerged leaves.
Many of the eggs you might find in your pond or vernal pool are likely Wood Frog eggs. It takes Wood Frog eggs 2-4 weeks to hatch. During that time, the embryo develops into a tadpole, which then breaks free of the jelly casing. In its stomach is the remainder of the jelly from their egg as they chewed through it, which sustains them for the first few days of life while they cling to plants and get used to their new world. After a few days, they grow strong enough to begin to swim around and look for algae to eat. Over time, they begin to lose their gills and develop lungs and teeth. As they grow bigger, they also begin to develop back legs and use their new teeth to become carnivorous, eating aquatic bugs and invertebrates that they find swimming around. It can take anywhere from a few days to a couple weeks for their back legs to develop fully. After their back legs are grown, they grow their front legs. Finally, the froglet will begin to absorb its tail and turn it into protein to allow the body to grow even more.
This entire process from tadpole to adult frog varies by species and conditions, but on average takes around 14 to 16 weeks for them to make this transformation. As an adult frog with strong legs and lungs, they transition to a life where they go on land much more often. An adult frog is usually 3 or 4 before it begins to lay eggs of its own.
Some research suggests that if the conditions aren’t right for tadpoles to turn into frogs, their bodies slow down and delay metamorphosis. Some conditions that they think might control this are water temperature, how many tadpoles are in one area, diet, and physical stress. When the water is warmer it may speed up how fast tadpoles turn into frogs, and the opposite may be true when there are too many tadpoles crowded in one place. Some tadpoles can even overwinter and 2 years as a tadpole! Frog species that are in temporary pools and wetlands that dry up during hot summers have to race against the clock to metamorphosize, like woodfrogs, peepers, and toads, while species that can often be found in permanent ponds like bullfrogs can take their time to change!