Of Birds and Snails

written by Ranger Andy Kilmer

Hi Friends!

Previously a rare sight along the Silver, some of you have noticed increased numbers of a familiar icon! The Limpkin, also known as limpkin-crane, crying bird, and the mascot of the Friends of Silver Springs, is a heron-like bird with a loud, crying call that ricochets up and down the rivers and lakeshores of Florida. But why the sudden return? It’s mostly to do with the Limpkin’s favorite food, apple snails.

Apple snails are a group of mollusks found in the tropics around the world with one species native to the Florida peninsula. They’re large and round, reminiscent of an apple! They are amphibious, with both gills and a lung-like pouch which allows them to feed and avoid predators both above and below the water.

The algae-eating, nocturnal Florida Apple Snail was once very abundant in the Everglades and in peninsular Florida where water levels remained relatively stable, like lakes, river swamps, and other large wetlands. Dams, canals, and encroachment by humans greatly impacted the native population, sometimes for the better, but generally for the worse.  South Florida, the heart of apple snail habitat has been hardest hit, with fluctuating water conditions and lots of development in recent decades.

To add to these issues of habitat loss facing the Florida Apple Snail, several competing species have come into the picture. Popular in the aquarium trade and with origins in South America, hobbyists had difficulty identifying these snails, so they were sold as “Mystery Snails”. Released or escaped, these species showed up in South Florida in the 1980s. The invaders are more generalized in their diet and habitat preferences than the natives.

The most abundant newcomer is the Island Apple Snail, which has made its way into many of Florida’s watersheds, out competing and displacing our native snails. They breed quickly, denude wetlands of all kinds of aquatic plants (not just algae), and can successfully invade areas that are more ephemeral and dynamic like prairies, small wetlands, canals, and even irrigation ditches. While you might see native apple snails on the Silver River, these days you’re much more likely to see the Island Apple Snail. Telling the difference is often difficult, even for malacologists, people who study mollusks.

Some say they can tell the difference between native and invasive snails by the color of their egg masses laid on emergent aquatic plants, but this is more difficult than you might have heard. While it is true that they are different colors and sizes, the eggs change colors at different stages of maturity. Florida Apple Snails generally have whitish eggs, but they are salmon colored when first laid. Island Apple Snails eggs are laid bubblegum pink but also turn white just before hatching.

While the native snails are in decline, species that rely on them are benefiting from the increased numbers of invasive snails. Limpkins think they’re tasty, no matter what! Snapping turtles and alligators also prey on snails. Another bird that has benefited from the booming snail population is the Snail Kite, which feeds on them and almost nothing else. While their population mirrored the decline of native snails, these small, hook-billed hawks have increased in number and expanded their range northward with the invasives. Just north of us at Paynes Prarie, a boom in Island Apple Snails post-Hurricane Irma has led to the largest congregations of Snail Kites in the US in decades.

The impacts of the exotic apple snail invasion are complex and dynamic, with positive and negative effects on the wetland ecosystems of Florida. Hopefully a new equilibrium will be reached that will maintain the balance and mitigate the loss of plant and animal species. Continue to watch the riverside. What changes have you noticed?