I was cleaning my garden pond in Staffordshire, UK, at the end of October and came across a live tadpole. I had previously suspected that some tadpoles are late undergoing metamorphosis, but this one really missed the boat. Is this a recognised phenomenon, and what is the explanation?
鈥� One has to assume that this is a tadpole of a frog or a toad, although it could have been the larvae of a newt, which is not dissimilar to a tadpole, except that it has feathery external gills.
That said, there are only two species of toad, the natterjack and the common, and three species of frog, the American bullfrog, the marsh frog and the common frog, recorded for Staffordshire. We can discount the toads, because both breed early in the year and a garden pond is unsuitable for a natterjack. For the frogs, the American Bullfrog has only been seen once in Staffordshire, which leaves us with the marsh and the common frog as the likely culprits.
Advertisement
There are frogs that overwinter as tadpoles in ponds, and one of these is the marsh frog, but once again we have the wrong habitat. That makes the common frog the most likely candidate. This normally breeds early in the year and has usually metamorphosed before late August.
However, overwintering is not an uncommon phenomenon and has been documented pretty much throughout the UK. It seems that the tadpole gains an advantage by deliberately delaying metamorphosis and overwintering, because it then emerges as a larger frog than usual. They may be able to do this because of warmer winters brought about by climate change.
Terence Hollingworth, Blagnac, France
鈥� Frogs and toads lay eggs, called spawn, in early spring. These hatch after a couple of weeks and the tadpoles grow and metamorphose to form miniature versions of the adult form. Transformations also occur inside the animal as its internal organs alter to cope with a changing diet.
Sometimes metamorphosis can be delayed if environmental conditions are not conducive for maturation. Overcrowding, with resultant food shortages, and low water temperature may slow growth. Such tadpoles have to overwinter in their pond and, if they survive the cold, will complete their development the next spring.
Overwintering could bestow a survival advantage over tadpoles that hatch and mature in the same year. They may also get a ready source of food from the pond, as tadpoles are known cannibals (19 April 2014, p 16).
David Muir, Edinburgh, UK
鈥� This reminded me of a childhood episode. Nearly 70 years ago, I kept a large crock of rainwater and pondweeds in our yard in Bolton, Lancashire. In spring I used it to follow the progress of collected frogspawn, via tadpoles, into frogs.
One year, after our summer holidays, the crock was swarming with four-legged tadpoles at a time when they should long since have departed as frogs.
I recalled a book by Enid Blyton about wildlife, which suggested tadpoles needed iodine to mature, presumably because it is used to produce thyroid hormones. Those were the days when medicine cabinets stocked iodine for cuts and grazes, so I put a few drops of iodine in the crock. Days later, the yard was teeming with small frogs.
鈥淚 put iodine into the tadpoles鈥� rainwater crock. Days later the yard was teeming with small frogs鈥�
It might be interesting to discover the iodine content of Staffordshire鈥檚 ponds.
Elizabeth Poskitt, Woodstock, Oxfordshire, UK
We pay 拢25 for every answer published in 快猫短视频. To answer this question 鈥� or ask a new one 鈥� email lastword@newscientist.com.
Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address.
快猫短视频 retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format.
You can also submit answers by post to: The Last Word, 快猫短视频, 25 Bedford Street, London WC2E 9ES.