My Science School

 There are over 3500 species of frogs – and more are being discovered every year. Frogs have evolved in a wide range of sizes, shapes and colours that enable them to survive on land, water, and on trees. Some frogs are totally aquatic, and live only in the water. Some like the mole frog, cannot swim, and live only on land. Others live near ponds and streams, and are at home both on land, and water. But whether it is on land, water or on trees, frogs have mastered the art of survival through their camouflaging abilities, defensive mechanisms, and their adaptability.

  Usually, the female frog lays her eggs in water- often in underwater plants. She and the male then leave the eggs alone to develop on their own. In some species, one of the parents stays behind to watch over the eggs and care for the tadpoles.

            Some frogs build nests of different types for their eggs. An Australian frog builds a foam nest made by churning a mixture of water and mucus to trap air bubbles. Large circular nests of sand and gravel are constructed at the edge of streams by the Latin American tree frog. Some frogs are very good fathers. The males carry eggs from a moist place, such as the water in a cupped leaf, to a wetter place, like a pond. They may do this by placing the eggs on their back, in a pouch on their belly, or even in their mouth. Some males wait for the eggs to hatch, and then transport the tadpoles on their backs. Male poison arrow frogs take their duties as a parent very seriously. They guard the clutch of eggs devotedly, and carry out vital transportation duties too. In the case of the Darwin’s frog, the eggs develop inside the vocal pouch of the parent, and after hatching, emerge as young frogs, through the mouth!

 

   Generally speaking, frogs lay eggs in large numbers. However, this is not always the case. The number of eggs laid by a female frog depends on the way the eggs are fertilized, and an embryo is formed. It is this embryo that later develops into a baby frog or tadpole.

            Normally, the female lays her eggs in water, and the male frog sprays his cells over them. This is called external fertilization. A great number of eggs have to be laid for external fertilization, because many of the eggs may not get fertilized at all. However, in the case of some frog, the eggs are fertilized inside the female’s body. This increases the chance of fertilization actually taking place, and so, fewer eggs need to be produced.

            The number of eggs laid also reflects the amount of care that the parent frog gives. Those frogs that take more care of their young lay fewer eggs, as the babies have a greater chance of survival.

            Most frogs lay between 1000 to 2000 eggs at a time – the American toad lays 4000 to 8000 eggs in one clutch. On the other hand, the tailed frog lays only 28 to 50 eggs per clutch, while the Cuban frog lays only one egg at a time!

  To put it in a nutshell, frog lets are tadpoles that have almost lost their tails and that have developed legs. This happens when the tadpoles are around twelve weeks. Froglets still have a lot of growing to do before frogs. Between 12-16 weeks, the froglet totally absorbs its stubby tail, and leaves the water.

            Sometimes, the term froglet refers to a frog that skips the tadpole stage and emerges as a fully developed frog. The Namaqua rain frog is one such frog. The eggs are laid in an underground nest, and metamorphosis takes place inside the egg capsules with the young emerging as fully formed frog lets. The three toed Brazilian toadlet – which is not a toad at all but a frog – also have young ones that hatch directly from the egg.

   Metamorphosis is the change of shape during an animal’s life. In frogs, it refers to the change from the larval or tadpole stage, into an adult frog. Frogs and toads generally breed in the pond where they were born. The eggs – sometimes there are thousands of them – are laid in clumps called frog spawn. Hatching takes place about six days after fertilization, and the babies or larvae are called tadpoles.

            Tadpoles live like fish, and have a head, body, and tail. They live underwater, and breathe through gills. They feed on algae and tiny water plants. These lungs, and front legs too. They lose their tails, and begin to look like little frogs. By the time they are three months old, tadpoles have completed the process of metamorphosis. They are now adult frogs that are capable of breathing through their lungs, and living on land.

   Most frogs breed near water, but some do breed in unusual places. Tree frogs, for example, many lay their eggs in water that collects in tree hollows- or even in flowers like the bromeliad flower. The vase like shape of this flower allows water to collect inside, and some tree frogs, who never come down from the tree tops, will lay eggs in that water. The water will also be sufficient for a few tadpoles to develop.

            Some of the larger tree frogs of South America dig holes in the ground that fill up with water for the females to lay eggs in, and tadpoles to develop. Some species attach their eggs to leaves that overhang rivers and ponds, so as to prevent the eggs from being eaten by ground predators. The leaves are folded over and stuck together to form a tube for further protection. When the tadpoles hatch, they drop from the jelly right into the water!

 

   In cool climates, frogs generally breed in spring. This is because as the weather becomes warmer, water levels will rise in ponds, lakes and streams, and the warmer weather ahead allows the baby frogs or tadpoles to develop faster into adults. in the tropics, frogs generally breed during the rainy season as there will be sufficient water in all the pools and streams that had dried up in summer.

            During a breeding season, the female frog produces around 2000 eggs. It lays its eggs in water because the eggs do not have a hard protective shell like bird or reptile eggs. They are laid in jelly-like masses, and unless they are covered with water, they will dry up and die.

           Like frogs, toads also use camouflage as a form of self defense. The fire bellied toad is a green toad with black spots that blends nicely with the leaves and greenery of its habitat. However, its underside is a bright red and black- and this colouring gives this toad its name. Fire bellied toads secrete toxins from their skin, and they want potential predators to know it. When threatened, they rise up on their front legs and arch their back, and flip themselves over completely to display their fiery bellies. This is a clear warning to predators to keep their distance, or risk being killed!

The common European toad bluffs its way out of dangerous situations. When threatened, it stands on its toes and inflates its body with air making it look larger and more dangerous than it actually is. Toads can also excrete a fluid that acts as a self defense against any predators. That excretion may be foul tasting, or have a very mild toxicity. 

Frogs live in swamps, forests, and other places. These places are filled with the prey they need as food. More notably, these places also abound in predators which need frogs as food! Frogs have several enemies- snakes, otters, herons, badgers, hedgehogs and many other animals. Frogs therefore rely on the art of camouflage to avoid getting spotted by their enemies. Some blend with their backgrounds, while others even change colours to match their backgrounds!

The aim of camouflage is to break up the typical frog shape, so that the frog cannot be distinguished from its surroundings. That is why, very often, frogs are a mixture of browns and greens that make it difficult for a predator to determine where the frog ends, and the surroundings begin!

 Tree frogs are usually light green so as to blend in with the leaves, while a tree frog from Brazil looks like a splash of bird droppings on a stone! The Asian horned toad's colour matches that of the dried leaves and leaf litter on the forest floor, while it is practically impossible to see an African square marked toad if it remains perfectly still against a tree bark! In short, camouflage is important to a frog as it allows the amphibian to melt into the background and become practically invisible when danger approaches. 

      The legs and feet of frogs are adapted to where they live. We know that there are ground-dwelling frogs, aquatic frogs, arboreal frogs or those that live in trees, and burrowing frogs. In each case, the structure of their legs and feet vary greatly.

The legs of ground-dwelling frogs are designed for jumping. The three core bones of the hind leg are fused into a single, strong bone, and the limbs are elongated allowing the frog to apply force to the ground longer.

Burrowing frogs have short, muscular hind legs that they use primarily for digging. They also have a special hardened plate on each foot that they use like a Shovel to dig through soil. Tree frogs have sticky pads on the tips of their fingers and toes that help them grip tree trunks and branches. Some tree-dwelling frogs have specialized webbing between their toes that they used for gliding. Aquatic frogs have webbing too, which makes their swimming easier. 

Frogs generally jump or hop to move about. 'Rocket frogs' are so called because of how fast and far they can jump. The black-spotted tree frog is only 3.4 centimetres long, but can jump a staggering 1.5 metres! However, some frogs like walking frogs, get around only by walking slowly. And narrow-mouthed toads creep and crawl to their destinations. Frogs and toads have only five to ten vertebrae and almost no neck. Their front and back are fused together, and so are the two bones in their ankles. This helps them to leap, as it reduces the stress on the bones.

 Some frogs have webbing between digits to aid swimming. And the flying frog can actually glide from tree to tree with its modified webbing. Tree frogs have sticky, sucker-like discs on their hands and feet that help them to climb, and to cling on to vegetation.

Generally speaking, frogs move better in water than on land. A few burrowing species have short hind legs and cannot hop, but all other frogs have long, powerful hind legs, which they use for jumping. Did you know that many frogs can leap 20 times their body length on a level surface?

 Frogs will eat almost anything they can catch—but only if it's still alive. Most frogs eat insects, snails, and tadpoles. Large frogs will also eat small mammals, birds, fish, and reptiles. Most frogs hunt for food at night and hide during the day. Frogs don't drink water at all, but simply absorb it through their skin.

Frogs depend on their excellent eyesight to spot their prey. Once they sight it, a frog will even leap out of the water to catch its meal.

The frog will usually unfurl its long tongue that is coated with a sticky substance with lightning speed. The prey sticks to the tongue and is swallowed whole.

Though frogs have teeth, they do not chew their food. Their teeth are used only to hold the prey in place, and to keep it from escaping.

If a frog eats something poisonous, it is not too bothered. It just brings its whole stomach out of its mouth, mid wipes it clean with its foot!

Tiny mantella frogs are among the most brightly coloured and spectacular of all frogs. They come in many colours- inky black with brilliant splotches of orange, bronze, yellow, blue, or emerald green. By having the bright colours of the more toxic species, the frogs are avoided by predators. Mantellas secrete enough toxins to make a predator sick or, at the very least, they can make themselves taste quite bad!

 Must frogs have webbed feet to help them swim, but not mantellas! Because they spend their lives crawling around on land or in leaves instead of swimming, there is no need for webbed toes. They also have short legs designed more for climbing than for long hops.

Mantellas are found only on Madagascar, off the eastern coast of Africa. Like all amphibians, mantellas have skin that soaks up water. If something happens to change the water, amphibians are one of the first species to feel it. Mantellas are important to Madagascar because their health can help scientists determine the health of Madagascar's rain forests, air, and water-ways. 

    Poison dart frogs show off some of the most brilliant and beautiful colours on Earth. Their colouring can be yellow, gold, copper, red, green, blue, or black, depending on where they live. There are more than 100 species of poison dart frogs, varying in colour and pattern. The black and green species have black spots, the strawberry or blue jeans frog is all red with blue legs, the yellow-banded species appears painted with yellow and black. Colour shades vary among frogs within a species. It is the skin that contains the frog's poison.

 

Continue reading "Why are poison dart frogs important?"

The glass frog is a tiny frog that gets its name because of the translucent skin on its underside that allows you to see its inner organs, right down to its beating heart! This translucent skin makes the glass frog very difficult for predators to spot, as it almost becomes a part of the leaf it is sitting on.

Glass frogs are very small, the average one being between 1.4 centimetres and 3 centimeters, and they generally live in the rainforests of Central and South America. They are at a high elevation, so these rainforests are called cloud forests as the canopy is wrapped in cloud - and this is a further reason for which the glass frog's transparency is very useful. Although they live by streams and rivers, almost all glass frogs live in trees, only coming lower down to breed.