Spring Egg Mass Identification in the Great Northern Forests
With winter concluding in Northern New England and already past farther south, amphibians in the northeast are migrating to their breeding habitat and beginning to lay eggs. Many of the species that breed in the early spring seek temporary bodies of water to lay their eggs, such as vernal pools, which dry during the summer and are free of fish that eat amphibian eggs. While most frogs and salamanders only spend a brief period of time congregated at breeding sites, the eggs will remain behind for up to a few weeks or so, which makes the eggs a useful way to tell which species live in an area if you know how to identify them. Thankfully, is not very difficult to tell most eggs apart once you learn their field marks, which is what I will show you in this post.
This post is intended for use in the northeastern United States and covers all of the spring-breeding species found in Northern New England, but is also useful farther south, although the farther south you are the more species you may encounter. The post does not deal with mid-summer breeders such as Bullfrogs and Green Frogs, or species that do not lay noticeable egg masses such as Eastern Newts or Spring Peepers, which all lay individual eggs or groups of 2-3 eggs attached under leaves and debris. Keep in mind also, that egg masses deteriorate in form as they age and older masses may be tattered, torn, or completely separated into a film. First, I’ll start by teaching you about the difference between frog and salamander eggs, then move on to identification of each species.
Note: some photos depict egg masses that are in hand and out of the water. Removing eggs from the water can damage them and doing so is not recommended in most circumstances. These photos were taken to help people learn how to identify egg masses and the eggs were handled with incredible care. Removing eggs from the water is not necessary for identification in the field.
Frog vs. Salamander eggs
Northern Leopard Frog (applies to southern too)
American and Fowler’s Toad (also applies to other toads in the genus Anaxyrus/Bufo)
Frog vs. salamander eggs
Telling the difference between frog and salamander eggs is quite easy. Frogs lay individual clear eggs with a visible embryo contained within each egg. With frogs, the outside edge of the egg mass is made up of the eggs themselves. Spring-breeding salamanders in the Ambystoma genus take it a step farther and coat the entire egg mass with an additional layer of gel. These two photos demonstrate the difference clearly:
Salamander eggs. Notice that there is a layer of gel surrounding the mass of eggs. This protective film around the egg mass is characteristic of all salamanders in the genus Ambystoma, which includes all of the spring-breeding salamanders you’re going to find the eggs of. If you look closely, you can still see the clear outline of each egg within the mass:
This extra layer of gel on salamander egg masses is thought to provide the eggs some protection against predators such as the dreaded Eastern Newt, which apparently just eats its way past the gel anyway:
You would expect to find Wood Frogs breeding in ponds, vernal pools, and marsh edges in or near forested habitat at a wide range of elevations as soon as the snow melts and the ground thaws. A typical egg mass can have between 500 and 2000 eggs. The embryos start out black on top and white on the bottom, as do most open-water amphibian eggs, but as the embryo develops into a tadpole the white is lost. A fully-formed mass that has been in the water for a day or so is about the size of a softball and the clear space between the embryos and the margin of each egg is many times greater than the width of the embryo.
When Wood Frog eggs are laid, however, the masses are much more compact. Obviously a golf ball-sized frog isn’t going to lay a softball-sized egg mass. Directly out of the frog an egg mass is smaller than a golf ball, but swells to full size within hours.
Leopard Frog eggs look a lot like Wood Frog eggs with a couple key differences. The embryos are about the same size (2-3mm), but the eggs themselves are much smaller and tighter. The clear space between the margin of the eggs and the embryo is usually the about the same thickness as the embryo itself (remember, the clear space in a wood frog is much greater). Because Northern Leopard Frogs lay more eggs per mass than Wood Frogs (2000-4000), but the eggs are much smaller, the entire egg masses end up being about the same size (roughly baseball to softball sized). To the best of my knowledge, Northern and Southern Leopard Frog eggs are indistinguishable from each other.
Leopard Frogs typically lay their eggs in lake and river floodplains where sedimentation and silt can build up pretty quickly. Remember that Wood Frogs tend to breed in ponds and vernal pools. Sure, there is some overlap in breeding habitat between Leopard and Wood Frogs, but knowing the typical breeding habitat for each species can help in many cases.
Pickerel Frogs have very similar egg masses compared to Leopard Frogs, but notice how the Leopard Frog eggs are black on top and white on bottom. Pickerel Frog eggs are brown on top and yellow on the bottom. Other than that the eggs are pretty much the same.
If you can identify Leopard Frog eggs you can identify Pickerel Frog eggs. The egg masses are almost exactly the same except instead of the eggs being black on top and white on bottom, Pickerel Frog eggs are brown on top and yellow on bottom, which is unusual for amphibians that lay eggs in the open. Pickerel Frogs are usually found in upland habitats, typically breeding in the margins of ponds, small lakes, and wetlands, compared to Northern Leopard Frogs which most often breed in lowland floodplains. Habitat counts!
You might read that Pickerel Frog egg masses are plinth-shaped. If it weren’t for this obscure analogy, I would not even now the word “plinth”. Other sources say the egg masses are spherical, which is more consistent with my observations. For whatever it’s worth, this is a plinth, and now you know:
American Toad and Fowler’s Toad
Anaxyrus americanus and Anaxyrus fowleri
In the northeast, American and Fowler’s Toads are the only frogs that lays their eggs in a long string. A single strand could have between 2,000 and 20,000 eggs depending on the size of the female. Breeding occurs in the warmer months (mid-summer in Vermont). As far as I know, there’s no telling the difference between American and Fowler’s Toad eggs. If you live in a place with both species then you can use habitat as a clue, but not a very reliable one. American Toads TEND to be found in hardwood forests with loamy soils. Fowler’s Toads TEND to be found in coastal or floodplain habitat with sandy soils. The two species can also hybridize. Go figure.
If sediments settle on the strands actually recognizing them as eggs can be challenging, but the curly shape is a good clue.
The habitat these two toads will lay eggs in is pretty variable, but it is worth mentioning they are the only frogs in the northeast that often lay eggs alongside flowing streams and the tadpoles exhibit schooling behavior. You can even schools of their tadpoles moving around in brooks, especially in the pools adjacent to brooks where the current is a little slower.
Spotted Salamander egg masses are made up of about 50-250 eggs, can be as large as a grapefruit, and are very dense/firm. Usually they are laid in ponds, vernal pools, and marsh edges where fish are absent or scarce, but you’ll find them in ponds with fish too. If you pick up a Spotted Salamander egg mass it will usually hold its shape in your hand. The eggs are usually attached to sticks, branches, and vegetation below the surface of the water. Like other salamander egg masses, an extra layer of gel coats the entire mass.
Even as the egg mass ages and the embryos develop you can see that it is firm and continues to hold its shape when pulled from the water. Interestingly, algae often grows on the inside of each egg, giving older eggs a greenish color and providing the embryos with oxygen.
Just like Wood Frogs, you’ll often fine huge numbers of egg masses all in one spot. Some Spotted Salamander egg masses are a grayish opaque color, which is caused by a genetic trait of the mother and is common in some areas.
Pure Jefferson Salamander egg masses (they hybridize with Blue-spotted Salamanders) are laid in masses of 20-30 eggs. Sometimes masses are laid in a line down a single stick and, once they swell with water, may fuse into one another and appear to make up a single mass. The masses closely-resemble those of Spotted Salamanders but, in addition to being much smaller with only a single layer of eggs around the branch, they are also not firm. If you pick up a Jefferson mass the eggs will run through your fingers or break off the stick before even making it into your hand.
And here is freshly-laid Jefferson Salamander egg mass next to the salamander who laid them:
A. jeffersonianum x A. laterale
Blue-spotted Salamanders do not lay egg masses. Their eggs are attached individually or in groups of two or three on the underside of leaves. Hardly anybody ever sees them, I don’t have any photos of them, and looking for them will kick up so much debris you may suffocate nearby eggs, so I wouldn’t bother.
However, they hybridize with Jefferson Salamanders and the hybrids do lay egg masses. The two pure species cannot breed with one another, but a hybrid line of almost entirely female salamanders can breed with either pure species (their reproduction is a very complicated subject that I’ll delve into another time). Hybrids more closely-related to Blue-spotted Salamanders will lay individual eggs or small clusters of eggs under leaf matter. Those closer to the Jefferson Salamanders will lay egg masses that basically look like those of pure Jefferson Salamanders, but the hybrid masses often have a high proportion of nonviable eggs that do not develop. The dud eggs are turn gray and swell up quickly. The gray swelling is caused by the water mold, Saprolegnia sp. Water molds can be seen in amphibian eggs of any kind but it is very common in Jeff/Blue-spotted hybrids. Here is a good photo of a suspected hybrid egg mass with multiple infertile eggs.
In addition to eggs, spermatophores are another sign that salamanders have recently bred. Spermatophores are small conical sperm capsules on top of a small piece of gel that males deposit on the substrate that females will pick up with their cloacas to fertilize their eggs. To the best of my knowledge, there is no easy way to tell the difference between the spermatophores of different species, however spermatophores found in wetlands, ponds, and vernal pools in the spring will all belong to one species or another within the Ambystoma genus.
These are not amphibian eggs, but bryozoa colonies are often mistaken for them. Bryozoa are colonies of microscopic animals similar, but not related, to corals. The colonies are firm, can have weird crusty-looking things on the outside, and never have embryos on the inside. They can be found in pretty much any body of water, but I have only seen standing water or places with very minimal current. People confuse them for amphibian eggs a lot, but now you know better.
If you go out to a vernal pool or wetland to look for amphibian eggs, I think the two most useful tips are to wear polarized sunglasses and to visit the site more than once. Polarized glasses reduce glare on the water’s surface and make it MUCH easier anything underwater. Timing can be very important, especially for some species that hatch quickly, so it is worth visiting a site two or three times to look for new species that might have been absent when you first arrived. Good luck out there!
That is all. Have fun herping! And remember to submit reports to your local herp atlas. For Vermont that would be this one: VT Reptile and Amphibian Atlas Project. Use google to find your own if you don’t already know.