I love it when my children remind me how exciting the little things in life are. Each year, I look for markers of Spring, and a big one for me is frog spawn. This year it appeared relatively late in our garden pond, and I dutifully noted the date in my diary (it was the 9th March). But to the children, frogspawn does not signify anything as boring as a date in the diary, comparisons drawn with other years. For me, it is interesting to note that the last time frogspawn was as late as this, the year was 2013 – the year of Amos’ birth. The children don’t care about dates; they drag me down to the pond. ‘Mummy, Mummy, look! Frogspawn. Have we got tadpoles yet? Will there be tadpoles tomorrow? Mummy! LOOK!”
I look again at the jelly blobs in the water, and this time I see.
Frogs are amazing. The whole thing is amazing. For months the pond is frog free. We come across frogs in the garden through the summer and we find the odd one in the pond, but from October the frogs disappear from sight. Then suddenly, one day in February or March, we wake up one morning to a pond that is exploding frogs. Where have they all come from? And how do they all turn up together? What is it that makes them decide today is the day? Definitely the weather and something to do with water temperature, but they are not totally predictable – there must be other factors.
And with the croaking pile of simmering frogs comes the spawn. The pond becomes a mass of jelly, each little blob with the potential to become a frog. Sometimes the frogs don’t make it to the pond and you can see piles of spawn on the ground (Star Sleet as it used to be called¹). Then you can see just how much spawn each frog produces. And there’s that question that always worried me as a child – how does all that spawn fit into one frog? If you spot the spawn early enough, it is possible to see it as very neat, compact balls rather than the looser jelly blobs that are created as the spawn swells in the water. It is more credible that the compact spawn could come from one frog, but still, hard to imagine. If you are lucky enough to see the spawn at this stage, instead of the little black ball at the centre, you might see a ball that looks white on one half and black on the other. This is because you are seeing the two poles of the embryo – the black looking animal pole where cell division is happening relatively quickly, and the white looking vegetal pole where yolk is located and where the rate of cell division is slower. Layers of cells develop and fold and with amazing rapidity become a little wriggling comma of life inside the jelly. If we bring frogspawn in a tank into our house, it takes only a week from spawning to emerging. At the temperature of our garden pond it only takes a while longer. How totally incredible, what amazing biology is happening thousands of time over just in our little pond, and how often I forget to wonder at it.
Then, as suddenly as the frogs appeared, they are gone, and the tiny tadpoles left behind have a still more amazing journey ahead of them.
I must never let biology cease to amaze me.
¹ Macpherson A Vertebrate Fauna of Lakeland 1892