The Wood Frogs Have Emerged!

If you are near a small pond or vernal pool (temporary body of water that typically dries up during the summer) during the next week, you may hear quite a commotion.

Wood Frogs (Lithobates sylvaticus) have emerged from their winter hiding places to mate. While some frogs, like the American Bullfrog and Green Frog, will call all summer long, Wood Frogs only call and mate during a narrow window of time in early spring. They are usually the first amphibians to emerge, congregating in shallow ponds and vernal pools in large numbers. Frog enthusiasts await that first evening in February or March when the temperature will be 50 degrees or higher, with wet or rainy conditions to herald the beginning of the frogs’ movement. It is not uncommon to hear a male Wood Frog calling from a pond still partially covered with ice.

Wood Frogs LBNC 030211Wood Frog Vocal Sac

Males arrive first, floating on the surface and calling. The call of a Wood Frog is raspy and sounds like the quacking of a duck, especially in a large chorus. Instead of one large vocal sac that makes their throat look like they swallowed a tennis ball, Wood Frogs have two separate vocal sacs called paired lateral vocal sacs. The vocal sacs act as resonating chambers, magnifying the sound so it will travel farther. Even with two vocal sacs, the Wood Frog’s call does not travel very far. This does not seem to be a negative factor in the crowded conditions of a typical Wood Frog chorus.

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Female Wood Frogs do not call. Instead of showing up with a lot of noise, the females show up with a lot of eggs. The heavy, almost bloated appearance of the female above indicates she is gravid, or full of eggs. Notice the pavement background in the photo above. Wood Frogs live in leaf litter and under logs and rocks in forested areas, not necessarily close to water. Some will travel significant distances to reach a suitable body of water to mate.

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When a male finds a female they engage in a mating behavior called amplexus. This behavior is important for Wood Frogs, because like most frogs they fertilize externally. When the eggs come in contact with water they immediately begin to swell and absorb the water. Once the eggs swell, fertilization would no longer be possible. The male needs add his sperm to the female’s eggs as soon as she releases them, and this is accomplished through the amplexus position. The male clasps the female under the armpits from behind. Once in amplexus, the male stimulates the female to release her eggs, while simultaneously releasing his sperm. The male typically will not let go until the female has released her eggs. It is not uncommon to see several males clasping the same female, or to see a male attempting amplexus with another species of frog, toad or even salamander.

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Wood Frog eggs look very different when they are first laid (pictured at left) versus when they have been in the water for a couple of days (pictured at right). The small eggs are attached to a twig or other submerged structure so they will not drift. The egg jelly (albumen) swells on contact with water. Since egg masses can contain as many as 2,000 eggs, it is beneficial that the eggs be as compact as possible while still inside the female’s body. The “inflated” egg jelly protects the eggs from physical injury, drying up and may also have anti-bacterial and anti-fungal properties.

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The embryos can easily be viewed, because Wood Frog eggs are so large. With some magnification, one can even view the development of the embryo.

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These eggs are just hours from hatching, and you can easily make out the shape of the new tadpoles inside. Once the eggs are laid, the adults leave the water to return to their forest home. The soon-to-be-hatched tadpoles are on their own. These tadpoles eat plant matter voraciously, and develop quickly into adults.

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With each egg mass numbering in the thousands, this would surely seem to be a recipe for overpopulation. With no parental care, however, Wood Frogs lay large amounts of eggs in the hopes that a few survive. One scientific study followed Wood Frog egg masses to adulthood, and found that survivorship was only 4%. The good news is that the hundreds of frogs you currently hear “quacking” survived those odds, and have returned to produce one of the truly great spring spectacles!

Snakes in the Basement

In late summer, young snakes often find their way into basements. Gulf Branch Nature Center is no exception. In the past two weeks we have removed several young Ring-necked Snakes (Diadophis punctatus edwardsii) from our basement, releasing them in the surrounding forest.

Even as adults ring-necks are small snakes, typically ranging 10 – 15 inches in length. Females lay eggs in a rotting log in early summer. The young hatch and must fend for themselves. Small invertebrates make up the diet of juveniles, while older snakes will also eat earthworms, small snakes, small lizards, and salamanders. They do not bite when handled, instead releasing feces or a foul-smelling musk from anal glands. This is easily washed from one’s hands, and these small snakes can be safely and easily removed from your home.

Other common snake species with young small enough to find their way into our basements include:

These three snakes don’t initially seem to have a lot in common. Northern Brownsnakes live under rocks and logs in forests, fields and suburban areas, feeding on slugs and worms at night. They rarely exceed 15 inches in length. Eastern Gartersnakes live in a variety of habitats including forests, fields, wetlands and urban and suburban areas. Their diet is just as varied, including invertebrates, fish, frogs, salamanders, and lizards. Gartersnakes can reach lengths of 4 feet. Eastern Ratsnakes can reach lengths in excess of 6 feet. They live in fields and forests. Excellent climbers, these snakes will feed on birds and bird eggs, as well as rodents.

What these three species do have in common is that they are nonvenomous and harmless. As juveniles they may feign a strike, never actually opening their mouth, but are far more likely to try to escape than bite. They also share the unfortunate coincidence of being mistaken for juvenile Northern Copperheads (Agkistrodon contortrix mokasen). Most tales of these mistaken identities do not end well for the snake.

Copperheads are mostly uncommon in Arlington, and juveniles can be quickly identified with two simple ID tips:

juv_copperheadThe first and easiest tip is to look for bright yellow on the tail. This bright yellow tip is used by young copperheads to draw prey in closer before striking. Second, note the presence and shape of dark bands on the back of the snake. They narrow as they approach the spine, producing an hourglass or saddlebag pattern. The nonvenomous snakes shown above have patterns with spots, not bands.

If you’re uncertain about a snake you have seen, check out this webpage about Northern Copperheads from the Virginia Herpetological Society: http://www.virginiaherpetologicalsociety.com/reptiles/snakes/northern-copperhead/northern_copperhead.php. It has an excellent set of photos comparing juvenile and adult snakes to copperheads.

You are far more likely to find a nonvenomous snake in your basement. Avoid using glue traps. Snakes suffocate and suffer needlessly in them. Even if rescued from a glue trap, a snake will often have severe and irreparable damage to its scales. Gently use a broom to guide snakes into a waiting bucket or box and deposit them outside, away from your home in a grassy or wooded area.

The Journey of the American Eel

American Eel

American Eel. Source: Wikipedia.org

The only fish you are likely to find in Arlington’s Gulf Branch is the American Eel. This has little to do with the water quality of Gulf Branch and more to do with heavy runoff after rains. The scouring action of rushing water after a storm makes it difficult for fish populations to maintain a foothold (or fin-hold) in the stream. Other streams in Arlington, such as Four Mile Run and Donaldson Run, also have eels, but Gulf Branch is probably the only one where the eels are the only fish you will encounter. This is also a result of the large, steep, rocky waterfall where Gulf Branch dumps into the Potomac, which acts as a barrier to most fish moving upstream. However, one could not ask for a more interesting or unusual fish to be found in Gulf Branch.

American Eels (Anguilla rostrata) have small pectoral fins and long, continuous dorsal and anal fins. Their long, slender bodies look far more snake-like than fish-like. A layer of mucus covers the eel’s skin, and its scales are small and well embedded in its epidermis, making them hard to see. The eel itself may also be hard to spot as they are typically nocturnal. American Eels are a generalist species as a result of their life cycle, and they can survive in a variety of freshwater different habitats including streams, rivers, lakes, estuaries and coastal bays. Their diet is just as varied and includes most aquatic organisms, living or dead, found in any habitat they may occupy.

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Eel in its natural habitat

The life cycle of the American Eel is an amazing story that spans miles and decades. These fish are catadromous, meaning they migrate from freshwater to the ocean to spawn. These eels hatch in the Sargasso Sea as small, nearly transparent and flattened larvae that look quite different from adults. The larvae begin a long, passive migration as currents guide them to the coastal waters of Eastern North America over the course of seven to twelve months.

Eels go through several morphological changes as they grow. As the eels grow larger and approach their new freshwater homes, they begin to produce pigment and darken in color. While their transparency made them difficult to spot drifting in currents along the open ocean, this new darker color provides camouflage against the dirt and rocks at the bottom of estuaries and rivers.

While most fish get flushed out as a result of stormwater in Gulf Branch, eels are accomplished, upstream swimmers. Natural barriers like waterfalls, and even human-made barriers such as smaller dams, are not always enough to stop the upstream migration of eels. Eels have been reported moving across short distances on land in wet or rainy conditions to get around waterfalls or dams. American Eels have been spotted in Gulf Branch upstream beyond Military Road. Their elongate body also helps them find shelter in cracks and openings too small ornarrow for larger fish.

Here they may spend 10-25 years maturing before beginning the return journey to the Sargasso Sea. As their body gets ready for the long journey, their pectoral fins enlarge for better swimming capability, their eyes enlarge to adapt to the oceanic environment, and their skin thickens to protect against the saline environment.

American Eels are semelparous. This reproductive strategy is also called “big bang” reproduction because it happens once, in a large quantity and is typically fatal. Female eels may produce 400,000-2,500,000 eggs. Adults die after mating and spawning in the Sargasso Sea, completing an odyssey that lasts more than a decade and covers hundreds of miles. Thankfully, the completion of their journey means the beginning of another, ensuring that Arlingtonians will continue to enjoy encountering this curious fish in our local streams.