Frog

## Frogs are fascinating!

There is a wonderful variety of frog species, each adapted to living in its unique habitat, be it cool mountain slopes, scorching deserts, or tropical rain forests. Depending on the species, they may be found in water, on land, or in trees and come in many sizes and colors.

## Frog or toad?

Frogs often have long legs that are good for hopping, skin that is smooth and moist, and special pads on their toes that help them climb. Toads, on the other hand, are more heavyset with shorter legs, and usually have drier skin, often with warty-looking bumps. Frogs are more likely to live in or near water than toads. The word "frog" can include both frogs and toads, as some frogs may not live near water and some toads have smooth skin.

Can you get warts from holding a toad? No! But you can die from holding a frog - if it's a poison frog! Some of these bright little South American frogs are so toxic that one drop of their skin secretions can kill an adult human. But don’t worry, as these toxins need to enter the bloodstream to cause you harm, and those in zoos are not toxic because they don’t eat the poisonous insects found in the wild that are required to produce the toxin.

## Special skin

Frogs and toads don’t have fur, feathers, or scales on their skin. Instead, they have a moist and permeable skin layer covered with mucous glands; this allows them to breathe through their skin in addition to their lungs. They can also absorb water through wet surfaces and are vulnerable to water loss through the skin in dry conditions. The thin layer of mucous keeps the skin moist and protects it from scratches.

Frogs need fresh water for their skin, so most live in aquatic or swampy habitats. There are always exceptions, though: the Australian water-holding frog is a desert dweller that burrows deep into the ground to keep from drying out. The waxy tree frog, found in the arid Gran Chaco of South America, produces a waxy substance that it rubs all over its skin to prevent evaporation.

## No necks

When you look at a frog or a toad, you'll notice that it doesn't seem to have a neck. Practically speaking, this is true. Most frog and toad species have large, protruding eyes so they can see in most directions. They can also hop around to look in another direction. But they can't turn their head like we can, since their neck is almost non-existent.

## A matter of survival

Adult frogs and toads have two main color schemes. Each one signals a different survival technique. Those with bright colors (like poison frogs) advertise their presence and warn potential predators that their skin is toxic. Those with mottled green or brown colors are camouflaged so predators have a hard time finding them. Some species employ both strategies, such as the Oriental fire-bellied toad, which is green on top but red on the bottom. When disturbed, these toads bend upward to display their red belly and warn predators of their toxic skin.

Toads have additional survival techniques as well. If a predator is after a toad, the toad can puff itself up, so it looks too big to swallow. Most toads can also secrete a burning milky toxin from a gland, called the parotoid gland, behind their eyes!

## Playing leapfrog

Most frogs and toads are great at hopping any which way. Powerful muscles in a frog’s back legs give it distance while pushing off from whatever surfaces it’s leaping from. Generally, the longer the frog’s back legs are, the farther it can hop. Hopping is a great way to escape from danger quickly. Some frogs prefer to walk or run rather than hop, especially those living in grasslands, and aquatic frogs use their swimming skills to make a quick get-away.

## What's for dinner?

Most frogs and toads eat insects, spiders, worms, and slugs. Some of the larger species chow down on mice, birds, and even other small reptiles and amphibians. At the San Diego Zoo and San Diego Zoo Safari Park, our frogs and toads are fed crickets, worms, fruit flies, or mice.

Frogs and toads are responsible for keeping a large part of the world's insect population under control. In some cases, however, their appetites can be a problem. Latin American cane toads were introduced to Australia in 1935 to kill sugarcane beetles. But instead of beetles, the toads preferred to eat native frogs, small marsupials, and snakes. Not only that, but they poisoned everything that tried to eat them, including rare animals like Tasmanian devils and pet dogs! Since cane toads lay more than 50,000 eggs at a time, they turned into bigger pests than the beetles they were supposed to get rid of.

## A ribbeting chorus

Have you ever walked past a pond or creek at night and heard lots of frogs croaking and ribbeting like a giant froggy chorus? It's likely you're hearing male frogs making calls to attract females. Each frog species has a different call that is used to attract mates and warn off rivals. When a female picks a male whose call she likes, the male grabs her and she releases her eggs. Then he fertilizes the eggs and, in some species, also guards them.

## When is a fish not a fish?

When it's a tadpole! Most frogs and toads start life in the water. The mother lays her eggs in water, or at least in a moist place like a dew-collecting leaf or plant. The eggs hatch into tadpoles (also known as pollywogs) that have gills and a tail like as fish but a round head. Most tadpoles eat algae, plants, and decaying organic matter, but some species are carnivorous and may eat tadpoles of their own or different species. Tadpoles gradually grow legs, absorb their tails, lose their gills, and turn into frogs and toads that start breathing air and hopping. This whole transformation is called metamorphosis.

## Dad takes the lead

In many species of frog, it is the father that cares for the eggs. He may transport the eggs to a safe, wet place by putting them on his back, in a pouch on his belly, or even in his mouth. Or he may wait until the eggs hatch into tadpoles before he transports them from a wet place on land to actual water. Although the father is more likely to perform these tasks, the mothers often do, too. Sometimes both parents do the babysitting - it just depends on the species.

Suriname toads have a unique way of caring for their offspring. Once the female lays eggs, the male frog holds on to her and pushes the fertilized eggs on her back, where they are absorbed into the spongy skin. This provides a protective layer for the larvae to develop. After three to four months, the now fully developed frogs emerge by popping out of the mother’s back!

The Australian gastric-brooding frog had one of the weirdest ways to care for eggs. The female ate as many as 20 eggs after the male fertilized them; she then stopped eating regular food because the eggs were developing in her stomach! When they began to turn into tadpoles, she vomited them up and started eating again! Sadly, this species has not been seen in the wild since 1981.