Visit a farm pond ringed with dense vegetation this month, and you’re sure to hear two distinctive sounds.
A booming “Jug-o’-rummm!” signals the presence of bullfrogs. The sound of a loose banjo string comes from an amorous male green frog. Though similar in appearance, bullfrogs can reach a length of seven inches; green frogs top out at about four inches.
Both sexes of bullfrogs vocalize, but the “jug-o’-rum” mating song of the male is the loudest and best known.
Other calls signal territory ownership, warning and distress. Bullfrog distress calls can be so long and loud that a biologist once wrote, “We hasten to release the frog, for fear our neighbors will accuse us of cruelty to children.”
Bullfrogs emerge in early spring, but delay breeding until late May. Their deep booming voice announces the eve of summer.
Any quiet body of water surrounded by dense vegetation is likely to shelter bullfrogs. Farm ponds ringed with cattails, water lilies or sedges are bullfrog heaven.
Males sing to attract females to their territories. Each male sings from a station along the bank that he defends and returns to night after night.
Mating occurs in the water. The male pounces on any female that finds his voice irresistible and grabs her tightly. He fertilizes the eggs, up to 20,000 of them, as she releases them. The embrace, which is typical of frogs and toads, is called amplexus.
The female simply releases the eggs on the surface of the water around pieces of aquatic vegetation. Eggs hatch in three to five days. Second broods are common.
After spawning in late May or early June, bullfrogs sometimes repeat the process in late July. Tadpoles reach a length of one inch by the end of their first summer. Before transforming into adults, however, they grow extraordinarily large.
Bullfrog tadpoles often reach lengths of six inches or more before metamorphosis after 12 to 14 months as tadpoles. Young bullfrogs then need another two years to reach sexual maturity.
Because of the time it takes bullfrogs to reach their large size, they require several years to reach reproductive age. The tadpole stage lasts one or two years.
Young bullfrogs then need another two years to reach sexual maturity. This means bullfrogs can be four years old before they breed.
Unlike most frogs, which eat small insects, spiders and earthworms, bullfrogs are voracious predators. They attack any live animal smaller than themselves.
A student of mine once found small turtles in the stomachs of several large bullfrogs. Other biologists have found mice, bats, lizards, ducklings, smaller frogs (including smaller bullfrogs) and even small alligators in bullfrog stomachs.
A sit-and-wait hunting technique rewards patient bullfrogs. They sit motionless for long stretches of time, yet remain alert to movement. If danger threatens, hop, splash and it’s off to the safety of deep water.
But if a crayfish, minnow or insect ventures near, it’s mealtime. And beware if you have a small backyard pond stocked with bullfrogs.
They do not hesitate to eat small birds, even hummingbirds, that stop by for a drink or a bath. Search “bird eating bullfrogs” on the Internet for video examples.
A bullfrog lunging out of the water for a bird reminds me of video I’ve seen of killer whales surfing onto a beach for a seal. On the other hand, water snakes, snapping turtles, raccoons, mink, otters, alligators and herons are just a few of the predators that eat bullfrogs.
Humans are also on the list. Frog legs are tasty and often found on menus at fine restaurants.
In fact, it is our taste for frog legs that has caused bullfrogs to become an ecological disaster in places where they have been introduced for commercial use.
In 1898 bullfrogs were imported to California to meet consumer demand. Since then, they’ve been released in Asia, Europe and South America.
In the absence of natural predators, bullfrogs thrive and disrupt wetland ecosystems all over the world.
It’s just another example of man tinkering with nature. Introduce an exotic species, and ecological chaos often results.