Herts Wildlife Trust: Frogs croak into action for spring

Common frogs mating

Common frogs mating - Credit: Tom Day

Able to hibernate underwater, grow a special sex thumb, metamorphose, and live on land, frogs are a natural wonder. And, as they are waking up near you, as Herts & Middlesex Wildlife Trust explain...

As we approach spring and the days warm, some amphibian are waking from their winter slumber. After five months in hibernation, frogs emerge back into the world in search of a mate. 

You may spot more frogs around ponds at this time, where they have been spending time conserving energy over the cold months.

Frogs can survive underwater during hibernation by absorbing oxygen through their skin. Remaining underwater also keeps frogs safe from predators and allows males to immediately claim territories when they awake. 

A male attracts females to a territory by croaking loudly and repetitively – you may hear several in one place.

There are often larger populations of male frogs, leading to aggressive battles to mate with the available females. During breeding time, males develop enlarged pads on their thumbs which help them hold on to females during amplexus - the mating position of frogs and toads, in which the male clasps the female about the back.

Once bonded, females lay many hundreds of eggs in a large clump which the male fertilises while still grasping his mate. 

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The breeding frenzy does not last long, but leaves thousands of eggs wallowing in the shallows of ponds.

As the eggs, or frogspawn, grow, they swell and float closer to the water’s surface. Eggs hatch within a week or so, becoming tadpoles.

Tadpoles feed on plant matter and will first lose their external gills and grow internal lungs, then feet and legs form, and they eventually lose their tails – a truly wondrous transformation.

Over the next couple of months they develop into froglets, feeding on flies and insects before leaving the breeding site and heading off to find food and shelter on the surrounding land. 

Give frogs a home

If you would like to see frogs in your garden and witness the sight (or more likely sounds) of the mating season next year, the best thing you can do is to build a pond.

Your pond doesn’t need to be big and can even be an old plant pot or sink. Building a water source into your green space will attract frogs, dragonflies and newts and support these wonderful creatures throughout the year.

How to build a pond

1. Dig a hole about 20cm deeper than required to allow for sand, matting and liner.

2. Calculate the size of the liner as follows: Length = length of pond + (2 x maximum depth) + 1m edging. Width = width of pond + (2 x maximum depth) + 1m edging.

3. Spread a layer of sand approximately 5cm thick in the hole. This will protect the liner. You may wish to lay special protective matting, which can be bought when you purchase the liner. Alternatively use a piece of old carpet or underlay.

4. Lay the liner across the hole. Handle it gently and only tread on it with soft-soled shoes or bare feet. Weigh down the edges with bricks or pieces of paving slab.

5. Fill the pond. As the water level rises, the weight of the water will pull the liner into the contours of the hole. Do not cut off any excess liner until the pond is completely full. When full, cover the edges of the liner with turf or paving slabs.

If you don’t have a large outdoor space to build a pond, you can still make a difference for wildlife. Follow steps to build a mini pond at wildlifetrusts.org