LIFECYCLE OF FROGS

1. The eggs (called spawn) are laid in early spring, each one in its own bead of almost clear jelly.  They cling together in a mass, which floats high in the water when it is newly laid.  Very often some of the spawn is above water level, but it stays moist and fresh.  It is anchored to plants, which prevent it from being carried downstream if the water is moving.  This spawn - there was enough to fill a litre jug - is two days old.

 

2. Half-way through their development, the round embryos have turned into elongated blobs, beginning to show a tadpole shape.  The mass has sunk lower in the water.  This gives more protection against frost, which often kills the embryos. 

 

3.  The embryos have developed gills, and the tadpole shape can be clearly seen.  You can now see that the little black shapes are alive, for they wriggle and squirm in their jelly beads, beginning to free themselves.  The jelly begins to turn in to one mass, instead of separate beads.

4.  Depending upon the weather, 7 to 14 days may pass before the babies - called fry - wriggle from the jelly mass.  There is doubt that they eat the jelly, certainly most of it is left behind.  They tend to collect in a ring around the edge of the mass, holding onto it whilst their strength is gained.  At this point the majority of losses may occur, the fry are an easy meal for any predator.  Notice the central eggs have not yet hatched.  If the ones in the middle hatched first, then the fry would damage the jelly beads of their brothers and sisters as they squirmed through them to free themselves!

 

5.  Two to four days may pass before the fry leave the jelly mass and really become free swimming.  They eat infusoria and algae, and grow at a very high rate.  These fry are in a cold room indoors, and therefore have grown on faster, they are only two days old.  

6.  Meanwhile, outside on a warm spring day, the young tadpoles are slow in both movement and growth.  They huddle in horizontal or vertical positions above and within the jelly as it slowly rots.  Look closely - a few empty globules of jelly can still be seen intact in the photo below, top-left of the writhing mass of fry.  The jelly provides a surface that encourages algae growth, on which the young feed, but more importantly, it provides warmth - a thermometer shows an increase in temperature of 2 - 3 degrees Centigrade within and immediately above the jelly.  Nearly three weeks after hatching the fry were beginning to wander  two or three feet away from the remains of the jelly - but a late fall of snow soon sent them scuttling back to the warmth of their old jelly "quilt"!

7.  Tadpoles have two aims in life.  They need, first of all, to survive.  This is not as easy as it sounds, for they are quite low in the food chain, and because they are slow (and not very smart!), they are easy prey for birds as well as other water life.  There second aim is to eat... and eat, and eat, and eat...  algae, debris, and plants.  Tadpoles must grow as quickly, and as large, as possible, so virtually all of their time and energy is spent eating!  The smaller they are, the more creatures there are that will eat them!  Similarly, when they turn into frogs, the bigger they are, the larger the prey that they will be able to catch and eat.  Their bodies grow quite round.

8.  It is now the middle of September.  These tadpoles have been in the water for nearly six months.  They are slowly changing.  Their bodies have become "frog-shaped", their legs are growing (the back ones grow first), and their colour is changing to a dappled or spotted browny-green.  Frogs are not all the same colour, and they can create their own camouflage by changing colour slightly to match their surroundings.  If the summer had been warmer these tadpoles would already have changed into little froglets, about the size of your fingernail, and left the water.  Some of them will be slower than others to develop, maybe even remaining a tadpole for the whole of the winter and following spring.  When they turn into frogs they will no longer eat a vegetarian diet.  If the weather is cold there will be no insects, slugs or snails for them to eat, which is why they hibernate for the winter months.

                              

 

 

 

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