So, you’ve got some tadpoles…?

John Skillcorn

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Running a Website as I do, one of the commonest questions I get asked is something along the lines of this:

'My little boy has been given some tadpoles to look after during the school holiday, and we are at a loss to know how to care for them.  Can you help?' or:

‘I sent off for a giant tadpole for my little girl and what we received was entirely unexpected. It’s huge and we don’t know what to do with it. It’s already eaten the cat. Can you help?’

The time of year this cri de coeur manifests itself depends upon in which of the earth's two hemispheres the questioner resides.  In the northern hemisphere it's around March to May.  In the southern hemisphere, it's around October or November.

So, for those people who have no idea how to look after tadpoles, here’s my attempt at shoving it all in a nutshell, albeit a fairly big nutshell.

These notes DO NOT refer to Dendrobatid frogs. They are purposely very general and should hold good for the majority of tadpoles commonly encountered by the average parent or naturalist. Also, although I refer mainly to ‘frogs’ these notes apply equally to ‘toads’ and also to a large extent to ‘newts’. There are slight differences in the latter animals’ development, however, which do not concern us here.

Finally, I am aware that many people who raise tadpoles will consider the following notes to be ‘over the top’. That’s fine, but I have reared many delicate tadpoles in what I consider to be a very healthy environment, and they have gone on to produce beautiful, healthy frogs with almost a hundred percent success rate.

Where do they come from?
A simple enough question, but one to which a lot of people can’t put an exact answer. Frogs from countries with a definite Summer/Winter usually hibernate. When the temperature starts to rise at the onset of the following Spring, the frogs begin to emerge from their hibernation quarters. This might have been the bottom of a pond or deep underground in an old rodent burrow, but generally anywhere they wouldn’t have been subjected to freezing temperatures.

Frogs from tropical countries might respond to a ‘wet season’, or they may be likely to attempt to spawn all year round due to the constant temperatures and humidity they experience in their particular habitats.

If they are not there already, they make a beeline for a body of water. Some frogs and toads will use any water available (large puddles, ditches etc.) while others tread a well-worn path to permanent water such as lakes, established ponds or even slow-moving rivers. It is at this time that road casualties become a significant factor in population losses. Movement to these waters usually takes place under the cover of darkness, but crossing roads is always fraught with danger resulting in thousands of amphibian deaths every year.

Once they arrive safely at their chosen site, the mature males begin to call. Their calls are amplified by vocal sacs – balloon-like structures under the chin or at the corners of the mouth. The pitch and volume of the call varies with the species of frog, but the volume of the sound has nothing at all to do with the size of the animal itself. Very small frogs can produce a surprisingly loud call. However, the overall effect of this is that the females become interested in certain males, and vice versa. Males also compete with one another for territories and females.

Assuming that a mature male has found himself an unmated female still full of eggs, he attaches himself to her by means of grabbing her armpits with specially roughened ‘thumbs’ called nuptial pads. With these he holds on like grim death and, in response to his squeezes, the female begins to lay eggs. As they leave her body, the male fertilises them by showering them with sperm cells. In this way, a single pair can produce several thousands of eggs and hence thousands of tadpoles. Sadly, and amazingly, only one or two will develop eventually into an adult frog. The rest will get eaten by a variety of animals, including sometimes their own brothers and sisters.

After a short time, the jelly surrounding the eggs absorbs water and swells. At the same time they float to the water surface to take advantage of the higher temperatures there, courtesy of the sun. In time – which varies from a couple of days to a couple of weeks depending on species – the eggs hatch into tiny ‘tadpoles’. These are not tiny froglets but wriggling, swimming, fully aquatic larvae, an intermediate stage between the egg and the baby froglet.

Now what happens?
This is where we come in. This is often our first encounter with the life cycle of a typical frog and we’re not sure how to deal with it under captive conditions.

In their natural habitats the young tadpoles will feed on vegetable detritus. That’s to say dead bits of water plants that are decaying in the pond. However, there comes a time when they will usually turn carnivorous (or often ‘omnivorous’ – see below) and their needs change. Their mouthparts also change to cater for this profound transformation in diet. This is also the most likely time when they will begin to feed on each other; especially at risk are those smaller and less healthy than the rest, and this is also most likely to occur in very crowded conditions. So how can we use this information to our advantage?

The container – this should be large enough to hold your tadpoles without overcrowding them. A thirty centimeter cube half-filled with water would accommodate up to ten tadpoles all the way through to metamorphosis (the time they develop into little frogs). What you put into your container should be kept to a minimum because you will be continually emptying and refilling it. So, a bare floor will be best (no gravel or sunken treasure chests – we’re trying to be scientific here) with a large handful of water plants such as Elodea (commonly called Canadian Pondweed) to offer both supplementary food and a secure form of cover amongst which they will no doubt hide.

The container can be stood in medium-bright light BUT NOT in direct sunlight. This would cause the water to overheat with the resultant loss of the tadpoles. Ordinary room temperature will serve perfectly well if your tadpoles are of species native to your country.

The water – should be either tap water that has been stood for a day in a clean watering can or other container, or rainwater from an outside rain barrel. Whichever is used, it is important that the temperature of the old water and the temperature of the new water be the same. This is normally achieved by keeping the old and new water in the same room. This water must be kept in a healthy state, as it will quickly become foul. See below. The water should also be crystal clear and rich in oxygen. The plants will help to achieve this, as will a low number of tadpoles and a large surface area of water. Tadpoles initially breathe using a combination of gills and the surface area of their skin. Later they will develop lungs and will be seen to come to the surface of the water to take gulps of air. At this time ‘mouthing’ the surface of the water can be used as an indicator that the water is low in oxygen for some reason – often as a result of decaying food or dead tadpoles. This is especially significant if it is accompanied by cloudy water which indicates a heavy population of bacteria.

The food – can be conveniently provided in the form of a good quality, flake goldfish food. My favourite brand name is TetraMin. This sort has a greater percentage of plant material in its make-up. You will get this at any good aquarist shop or even maybe a supermarket. The mixture of animal and plant ingredients in the flakes will cater for the tadpoles’ omnivorous tendencies, as opposed to carnivorous (strictly meat-eating) and herbivorous (strictly plant-eating) animals. An ‘omnivorous’ animal feeds on a variety of both animal and plant foods – we might describe ourselves as being an omnivorous animal.

Overfeeding – is something you must avoid at all cost. Give them as much as they will eat in ten or fifteen minutes then CHANGE THE WATER. Doing this makes sure that no food is left lying around to go bad and cause disease. Under ideal conditions you should do this twice a day. Something to remember, though, is the fact that flake food will tend to float, which is an undesirable characteristic as far as tadpoles are concerned. I avoid this by first stirring the flakes in a beaker of water taken from the rearing tank and then pouring the lot back into the tadpoles’ container. The flakes will sink to the bottom and will prevent your tadpoles swallowing bubbles of air - as they might when attempting to eat flakes floating at the water surface. But do remember that your tadpoles will get a fair amount of supplementary food from the water plants in their container as well as from the algal growth that will inevitably appear on the inner sides of their tank. So don’t be too bothered about cleaning the inside walls of their container.

Cannibalism – while on the subject of food, it is important to realise that tadpoles can – and will – become cannibalistic under certain conditions. This happens in nature so is sometimes unavoidable with some species. However, you can guard against this happening by keeping the population density of your tank low, keeping water quality perfect and by feeding your tadpoles regularly as described above. Some species of frog, for example the Dendrobatids to which this Website is dedicated, have tadpoles that are all naturally cannibalistic. For this reason they must be reared individually, each in its own separate container.

Growth – will be the natural result of ideal living conditions. The tadpoles will feed, get bigger and will change their physical characteristics over time. Their mouthparts will change to cope with a change in diet, but most astounding of all is the fact that they grow legs! The hind legs appear first as small buds at the base of the tail. Over a period of a week or so they will grow into large, muscular legs capable of making swimming movements. The front legs also develop at this time but, due to the fact that they are covered by the skin that also covered the gills, they do not become visible until later. Nevertheless, they eventually break through and suddenly appear fully formed. You then have a four-legged froglet complete with a long tail! It is at this time that the mouthparts undergo their most significant change. They transform from being those of a totally aquatic, omnivorous animal to those of a land-living carnivore. The froglets will now cease to feed while in the water but their further development is fuelled by the resorbtion of the tissue that has, until then, made up the tail. Once the tail has become a tiny vestige and is barely visible, then the final, major transformation takes place – the tadpole comes out onto land for the first time.

A terrestrial existence – is how we describe the froglets’ lives from now on. As soon as your froglets have four, fully formed legs and a long tail you must change their living conditions slightly. Providing they are all at the same stage, you can stop feeding them now. Also, you should either place a large, clean rock into the water with part of it breaking the surface or float a piece of expanded polystyrene in the container. Either way, your froglets will then be able to climb out from the water onto land for the very first time. It might be useful to now cover your tank with gauze to prevent premature escapes.

Incidentally, if you are rearing Mantella tadpoles then take care at this time, as these tadpoles often leave the water while the tail is still fully formed and before you were expecting it. They are liable to escape by climbing the walls of their container and hence die of dehydration.

Your charges are now land-living creatures and must now hunt and catch their own living, moving food. They do this aided by an extendable, sticky tongue that they can flick out, so trapping tiny animals and drawing them back into the mouth. The size of the food will of course depend on the size of the froglet. Baby Bullfrogs, for example, will eat much larger prey than baby Pool frogs. Indeed, baby Bullfrogs may well prey on baby Pool frogs! But usually tiny insects, worms, slugs, snails and so forth will all serve as suitable food items, so long as they are alive and MOVING. It is this movement that triggers the feeding response in the majority of frogs and toads. If it doesn’t move, it’s not regarded as food and will not be eaten. It should be obvious, therefore, that you must provide suitably small and living food for your frogs to feed on.

Many pet shops sell live crickets in a variety of different sizes, specifically bred as live food for frogs and lizards. The same is true of fruit flies, which are another important and useful food for small amphibia and reptiles.

However, if your tadpoles were obtained locally, now might be a good time to think about releasing your froglets back into the wild. Into your garden, for example, where they will assist in the removal of all manner of pests from your plants. If they are of a tropical species (and you don’t live in the tropics) then you will need to keep your frogs in a suitably heated and humid container. But I’m afraid that’s another story!