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Tadpoles and using them to understand brains

Tadpole Predators

Who is eating the tadpoles in your pond?


Tadpoles as food

Many animals get energy from eating other animals. When one animal eats another it is called a predator. The animal that is eaten is called the prey.


Many animals eat frogspawn, tadpoles and baby froglets leaving the pond. The animals that eat the tadpoles are their predators. Tadpoles are therefore the prey of these animals. Click here to play a tadpole game, where you have to eat as much as you can and avoid being eaten by predators in the pond.

Tadpole predators

Some examples of tadpole predators are listed below.

  1. Birds will eat tadpoles, such as this kingfisher with a tadpole in its beak.

Kingfisher_eating_a_tadpole_Pierre Dalous_creativecommons

2. Other pond life, including this great diving beetle and its larvae will hunt and eat tadpoles.  


3. Other pond life such as the dragonfly and damselfly larvae below (also called nymphs). 


3. Newts, like this smooth newt in the picture below will gobble up tadpoles if present in a pond. 

Common_Newt_-_Triturus_vulgaris_Ian Kirk

Click on the link to see a video from Arkive of a smooth newt eating a tadpole.smooth newt arkive

4. Fish will also eat tadpoles, for example young pike, sticklebacks and minnows in rivers in the UK.


If you have fish in your pond don’t expect to see any froglets leaving the pond, as all the tadpoles will be likely to be munched!

As you can see, many animals like to eat tadpoles! That’s why the female frog needs to produce so many eggs. Click here to learn more about why the female frog lays so many eggs.


Media credits: Banner-Markus@Thinkaholic; Kingfisher- Pierre Dalous; Great diving beetle- E van Herk; Great diving beetle nymph- Aflisch; Great diving beetle nymph eating tadpole- Giles San Martin; Newt-Ian Kirk; Stickleback- Ron Offermans; Minnow- Adrien Pinot.

Tadpole swims when touched at *

The details of swimming movements which hatchling Xenopus tadpoles make in response to touch with a fine hair  have been studied by making high speed videos at 200 fps. In these examples touch on the left (*) leads to a bend to the right followed by swimming. Waves of bending travel from the head to tail (at ~ 14 cm per second) and increase in amplitude as they travel along the body. They move the tadpole in the direction shown by the arrows. Swimming speeds at ~ 20 oC range from 4 to 6 cm per second.hatchling tadpole swims when touched at *

Kahn J.A., Roberts A. & Kashin S. (1982) The neuromuscular basis of swimming movements in embryos of the amphibian Xenopus laevis. J. exp. Biol.  99, 175‑184. http://jeb.biologists.org/cgi/reprint/99/1/175

Adult South Africal Clawed toad Xenopus laevis


         Xenopus laevis

What Tadpoles Look Like

Tadpoles can start swimming spontaneously or when they are stimulated but it is just as important that they can stop. This normally happens when their head and cement gland bumps into the surface of the water or some other solid tadpoles swimmingobject like a plant or the side of a dish. This kind of stimulus and the tension in the mucus strand when the tadpole is hanging attached have an inhibitory effect on the tadpole. While hanging, it never moves spontaneously and is much less responsive to stimulation. This ability to keep still may make it more difficult for predators to detect and eat tadpoles. 

Types of Neurons

There are different types of neurons in a nervous system and they are named depending on their function.


Interneuron from Xenopus laevis tadpole

Broadly there are 3 main types:

  1. Sensory neurons
  2. Motor neurons
  3. Interneurons 





Flexion behaviour of hatchling tadpole in response to skin stimulation (represented by arrow).

When the skin of Xenopus laevis hatchling is touched, sensory neurons are activated, passing on exitation to sensory pathway neurons (interneurons) in the spinal cord, which in turn excite motor neurons, causing flexion behaviour

For more info on research into flexion behaviour click here. 

Synaptic transmission (blank diagram)

pencil22small_foka.tkPrint and fill in the blank diagram with the key steps in the process of synaptic transmission:



Resting potential and action potential confusion!



The terms resting potential and action potential can be confusing, as they seem to suggest that one is an active process and the other not.


Action potentials are actually produced by a passive process- sodium ions diffusing into the axon, causing depolarisation. 

Resting potentials are generated by an active process, which needs ATP. The sodium-potassium pump carries out active transport of ions in and out of the axon to generate a potential difference across the cell and a voltage of -60/70 mV inside the axon.

So even though the axon is said to be at “rest”, an active process involving energy in the form of ATP is actually going on. And even though the action potential sounds like it needs energy, it is actually a passive process.

Make sure you are clear on this!

Axon, membrane or axon membrane?!



Some exam boards prefer you to mention simply the “axon”, others just the “membrane”, or the “membrane of the axon”. 


When we are talking about a difference in charge over an area, we always refer to what area that is- for example a potential difference over the axon membrane. 

Some exam boards will prefer you say that the “membrane” or “axon membrane is depolarised”…but others will be happy with just the “axon is depolarised”

Check what is preferred by your exam board and incorporate into your notes links below:





Exam Board Links

pencil22small_foka.tkClick on the links below to access the specifications for listed exam boards:







Toad spawn

Toad eggs are the same size as Frog eggs but are laid in a string, often among weeds in the pond. The string can be more than 1 meter long and contain a double row of eggs. Here is a photo of a small piece from a pond in Hampshire.

A small piece of toad spawn from a pond in Hampshire.

American Bullfrog

Below is an American Bullfrog. The Latin name of this frog is Lithobates catesbeianus. It is sometimes also called Rana catesbeianus. 

American_Bullfrog_(Rana_catesbeiana)_-_Algonquin_Provincial_Park_Ontario_By Ryan Hodnett Own work

Click here for more information on the American Bullfrog from the ARKive website.

Media credits: American Bullfrog-Ryan Hodnett