Belly up

Dead Broad-bodied chaser larvae in the pond yesterday (click the picture for a better view)

It’s natural to wonder whether you can have too much of a good thing – and when you’ve got thousands of tadpoles you do begin to wonder ‘Is that just too many? The usual answer is to say no, we’ll just let nature take it’s course.

But it seems quite likely that there will be some downsides when a small pond is occupied by a large number of the little squiggling munch monsters.

And what’s shown in the photo above may be one of those downsides  (sorry – only had a snappy camera available hence very bad photo, even by my standards!).

What you can see are two dead Broad-bodied Chaser larvae – belly up, having floated to the surface.

Here’s a closer view.

Tadpoles and pond skater feeding on dead Broad-bodied Chaser dragonfly larva

So far I’ve seen 4 and I can’t help thinking there may be a connection with the tadpoles – certainly I didn’t see anything like this last year.

I’m wondering whether the dragonflies simply ran out of oxygen – so will be testing the water soon to see how oxygen levels are going.

My mosses are also getting a severe haircut from the hordes (sorry – bit judgemental – how about ‘…..the crowd, or host…) of tadpoles.

Actually, although I’m a little sad to see the dead dragonflies I’m still happy to let nature ‘take its course’ – the sheer quantity of tadpoles is a spectacle, and I can tolerate a few casualties for now.

And also nothing’s wasted – as you can’t see in the second photo, the dead dragonflies are becoming tadpole food.

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11 Responses to “Belly up”

  1. Richard Says:

    Jeremy,

    What is the best thing to do if a pond starts to run low on water? Our water butt is now empty, if this dry spell continues should we top it up with tap water or just let get lower?
    There are no fish or amphibians in it, but a fairly healthy population of smaller creatures.

    Richard

    • Jeremy Biggs Says:

      Hi Richard

      If you’ve got this far with rainwater, I would let the pond go lower rather than top up with tap water (unless you have clean tapwater – check the water company data on your tapwater quality).

      One thing you might consider is whether you can scrounge some rainwater from other people.

      Lots of people have water butts which they don’t actually use – just make sure that its really filled with rainwater because sometimes people store tapwater in their water butts (the ideal is to check the conductivity).

      If you need any help with testing water quality or checking water company data remember that Pond Conservation supporters get this service free :-).

      Jeremy

      • Jackie T Says:

        I have a garden pond and have always had loads of tadpoles. Last year i spotted my first newt. This year I have loads of newts and the tadpoles all vanished soon after hatching. Should I help the frogs by collecting some spawn next year and letting it hatch in an aquarium or should I let nature take its course?

  2. Tristan Hatton-Ellis Says:

    Jeremy, I’ve never seen tadpoles kill a dragonfly larva before! I just had a look in my copy of Corbet – probably the definitive work on dragonflies. Here’s what he has to say [my comments in square brackets]:

    “Behavioural stresses to respiratory stress can be prompt and conspicuous. A larva of Anax imperator [Emperor Dragonfly] tries to move away from a concentrated source of carbon dioxide [such as a lot of tadpoles!], but if exposure continues, Vn [the “breathing” rate] is disturbed; in a few minutes the larva begins to float, and soon Vn stops altogether. When the source of stress is removed the larva can recover… At 17-18C and low oxygen concentration, a larva moves to the water surface and continues Vn with the tips of the anal pyramid protruding into the air.”

    So it’s possible that these larvae were poisoned by carbon dioxide rather than low dissolved oxygen. Other possible factors could include temperature and ammonia. In practice it’s likely that this number of tadpoles causes pretty poor water quality as measured by quite a number of factors. Have you noticed any other dead insect larvae? Mayfly larvae would be obvious candidates.

    Ref. Corbet PS (1999) Dragonflies: Behaviour and Ecology of Odonata. Harley Books.

    Regards, Tristan

  3. Sue Plaxton Says:

    Yes, I too have masses of tadpoles in my pond. Would introducing native fish be a solution i.e. to help balance out populations, or could they in turn become a different problem in the future? If fish are a solution, what species are best for smal ponds?

    Regards

    Sue

  4. Tristan Hatton-Ellis Says:

    Sue, be glad that you have so many tadpoles! Amphibian numbers are collapsing worldwide and anything that reverses this trend is to be welcomed. The tadpole numbers will sort themselves out and amphibian recruitment tends to be variable from year to year anyway – here in Wales a lot of spawn has been killed by cold weather. Plenty of predators eat tadpoles including water beetles, dragonfly larvae, water boatmen and newts, so the tadpoles will nourish the whole pond ecosystem.

    I don’t advise adding fish. They will either go the same way as the dragonfly larvae, or else will eat all the tadpoles. Most small ponds naturally lack fish in the wild.

    Tristan

  5. Judith Says:

    I have exactly the same dilemma as Jackie T, and I didn’t let nature take it’s course, as I am sure we would be advised to do, because I am trying to rebuild our frog population after suffering huge losses last year. Just 20 frogs returned to spawn instead of the 100-150 we normally get.
    I usually put spawn into a large tank of rainwater and oxygenating weed to hatch, so I can protect it from drying out or severe frost, but this year I also put all my tadpoles into 3 new small shallow ponds, and the newts all seem to prefer the deeper pond, so they are all thriving up to now.

  6. Jeremy Biggs Says:

    Hi Judith

    4 ponds instead of one sounds like my kind of solution.

    Jeremy

  7. Jackie T Says:

    4 Ponds! I don’t know how big a garden you have, but I would have all ponds and no garden!

  8. Susie Says:

    We have quite a small pond which this year has been overrun with tadpoles-literally a black writhing mass at the surface. After getting back off holiday one of our fish was floating dead and being eaten by the tadpoles. We thought it had died naturally – but then we have seen the tadpoles literally eating another of the fish alive. Two more then died and were eaten by the tadpoles so we had to take drastic action and remove hundreds of the tadpoles from the pond. We still have many there and I think they are still having the odd nibble from the remaining fish. Should we remove more? Why is this happening? We’ve never had many tadpoles survive before and no probelms at all. Should we add some food to the water? It really has been very disturbing.

  9. Jeremy Biggs Says:

    Hi Susie – I think probably your tadpoles are tidying up dead (or nearly dead) things rather than overwhelming your hapless fish – so I don’t think you need to worry that you’ve had an attack of the killer tadpoles.

    Tadpoles will feed on anything dead, animal and nutritious – and a dying or ill fish, probably covered in microscopic fish parasites, bacteria and fungi, would be a veritable feast for tadpoles which would graze this nutritious (to a tadpole) coating from the body of the fish.

    It is possible that your tadpoles were indirectly contributing to the demise of the fish – by simply over-stressing the system, using up a lot of the oxygen and releasing waste products into the water (I’m not certain that tadpoles produce ammonia – it wouldn’t surprise me if they do – and ammonia is very toxic to fish).

    Alternatively something else may have stressed your fish and made them unwell – and once stressed fish can quickly succumb to parasites and diseases.

    I think if you feed the taddies a bit (but make sure that the food doesn’t simply sink to the bottom) they may lose interest in the fish. But I’ve never been in this situation so I’m only making an educated guess here.

    But if there are very large numbers of taddies any passing fish covered in fungi and bacteria may be a temptation.

    But I don’t think they’re actively killing your fish – maybe only eating the nearly dead!

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