disappearing tadpoles

[amanda berry]

Last year all my tadpoles seemed to disappear and not develop into froglets. You all gave me wonderful advice about cutting out a lot of the weed - and being more patient with my searching. So I did as I was told and I did find a couple of froglets. But numbers were seriously down on previous years.

This year it is the same - I started with five large clumps of spawn - masses of tadpoles, but hardly saw any developing back legs. There are very few tadpoles left - this evening I have seen three large ones (no back legs even) and one very small froglet.

The pond looks really healthy and is supporting life. There are lots of efts - spotted about twenty tonight - so it can't be diseased. There are some big frogs too.

I also have a tiny pond and I haven't seen a tadpole or froglet recently in this one. But several big frogs look happy.

Why is this happening and what can I do? I am really pleased about the newts but very sad about my lack of frog - or rather potential frog.

My pond is about 5ft x 4 ft and not overshadowed by trees. The smaller one is quite shady and only about 2ft diameter

[Littlesparrow]

I don't know where you are in the country, but in Cheshire this year we had a very cold winter followed by a dry Spring. I covered my pond over when the temperatures dropped below zero for weeks at a time otherwise I think it would have killed the frogs and frog spawn.
Other than that your pond seems big enough and I'm sure you have been given good advise on providing plants and watching out for leaves falling in it and fouling the water etc.

[Dogghound]

Ive noticed very staggered emergence dates this year. I think you will find they are leaving the pond in small groups rather than large emergences like normal. This means they are less obvious, if that number of tadpoles were dead in your pond you would notice it especially in a small pond where the water quality would drop. Naturally predators kill many tadpoles in the pond so you might only get about 2 clumps worth of tadpoles emerging from your pond anyway.

[Malcolm Banks]

I had more than double the number of eggs laid this spring compared to last, but have very few surviving taddies and have seen only a handful of froglets.
However, picking up an element of Dogghound's comments, I did collect nearly 40 Aeshna spp. exuviae around the pond over this summer (the 3rd for my pond). So, if you also include the doubling in the number of my smooth newts, I reckon the poor old taddies took a bit of a bashing.
Have seen a female Great Diving Beetle (D. marginalis) in the pond lately, so next year's taddies may be in for a rough old time too
M

[Malcolm Banks]

PS - forgot to say that despite all this apparent carnage, my pond is populated by a large collection of frogs of various sizes - it all balances out in the end
M

[amanda berry]

Thanks for all comments - but what is 'Aeshna spp. exuviae' and do I want it?
I have had a really good look in both ponds and only found one froglet in each. In other years (over 2 years ago though) I've seen lots of them. I do have thousands of what look like woodlice that swim - not sure what they are.

How will I know if I have a great diving beetle?

[Malcolm Banks]

Aeshna is a genus of large hawker dragonflies whose larvae are also large. They live in the pond, are voracious predators and tadpoles are definately on the menu. The exuviae are the larval cases (exoskeleton) left behind on vegetation surrounding the pond when the adult dragonflies have emerged to take flight. I cannot imagine anyone not wanting to see the beautifully coloured adults flying around the pond. There may be occasional increases or decreases in their numbers locally, but over years (with all else being equal) these should balance out, the major arbiters being food supply and climate (which are anyway linked), and predator numbers.
At ca 30mm in length, Great Diving Beetles are not difficult to spot, but they tend to prefer larger ponds, so it may be that your pond may be a little small for them. The larvae of the GDB can reach 60mm, and they are also voracious predators.

I think water lice prefer running/moving water but yours could also be waterboatmen of various kinds?

I am not saying that all or any of the above are the cause of your tadpole/froglet crash, but as Dogghound says, predator numbers can significantly affect the number of your taddies that reach froghood. These things have a way of balancing out though, although climate change may adversely/beneficially affect some species more than others. The real sign of damage from whatever cause to your pond ecosystem is in the number and age of frogs you have in and around the pond. Do you have a range of sizes of frogs or are they all fully grown?
M

[amanda berry]

Thanks - that was really interesting, there is so much for me to learn! I do have a range of frog ages / sizes - though I haven't seen some of the smaller ones recently - not sure if that's because I just haven't seen them or because of a neighbour's active cat. We are going to buy a cat scarer as we are convinced know some of the frogs disappear in that direction... And I used to love cats.

I haven't seen a GDB - but presumably that would also enjoy the efts as well. I think you are right about them being water lice - there are a huge amount of them. we don't have boatmen but there are a lot of pond skaters.

I have also removed some of the large plants around the smaller pond to see if more light helps next year.

[amanda berry]

dear doghound

" you might only get about 2 clumps worth of tadpoles emerging from your pond anyway"

Not sure what you meant by that - are you saying that 2 clumps of frogspawn out of the five tadpoles will become froglets? Seems a huge amount. If thats the case there is something seriously wroing with my very healthy looking pond

[Dogghound]

Hi Amanda. Yes the number of tadpoles emerging is much lower than the number of eggs laid. This obviously varies per pond so that was more of an example. Have you had a good look through the undergrowth in your garden to see if you find any froglets?