When the Frogs Go, the Snakes Follow

Whenever I tell people about the devastating declines in amphibian populations around the world, there’s always someone that asks “So what?”. In other words, when the raucous chorus of breeding frogs stops, and the ponds fall silent at night, will we notice any other changes?

The answer is a resounding “Yes”. Adult amphibians eat an enormous amount of insects (including major agricultural pests), and tadpoles alter stream and pond dynamics, reducing algae and mosquito larvae, and even influencing sedimentation. Amphibians of all life-stages are also incredibly valuable food items for a range of animals. As amphibians can also reach high densities and biomass, they are very important prey for the survival of many species.

Some of the biggest amphibian-consumers are snakes. Around the world, many snakes feed primarily on amphibians, and many more regularly prey on amphibians when they get a chance. Garter snakes of North and Central America are heavily reliant on amphibians as food. Asian Pitvipers often eat frogs, especially when young, and Asian Keelback snakes are voracious frog, and tadpole, eaters. There are even snakes in Central America that specialize in eating the sticky egg masses laid by frogs on leaves overhanging streams (these snakes are sometimes appropriately referred to as “Goo-eaters”).

I know from experience that where there’s frogs, there’s snakes. By calling to attract females, male frogs also attract unintended visitors such as curious amphibian biologists and hungry snakes.

The dependence of many snakes on amphibians means that when the frogs ‘croak’, many species of snake will follow. In Central America, where amphibian declines have been most dramatic and well-documented, species of frog-eating snake that were once relatively common are no longer seen. Particularly where snakes can’t use an alternative food source (either they can’t or won’t eat anything else, or nothing else suitable exists where they are), amphibian declines pose a real and terrible threat to snakes. And snake population declines initiate a new range of environmental effects.

Amphibian population declines and the subsequent snake population declines provide a very real and current demonstration of the interconnectedness of ecosystems. You simply can’t alter one part of the environment without far-reaching, complex and often unpredictable effects.