What's That Bug? does not endorse extermination

Any ideas please ?
Hi Bugman,
I love the site, but I’ve not been able to find this in the alphabetic list or with the search – can you help at all please ? When I saw them I assumed they were dragonfly larvae, but now I’ve had a chance to look up the identification I don’t think they are – several points don’t match. There were 3 of them, in a small seasonal pond in South-West Scotland this morning – busily eating the tadpoles. I’ve not seen them before, and unless they’re something interesting I’m tempted to beat them to death before they finish off the last of the taddies. I was there about 4 weeks ago (and so were the tadpoles), and I visited at least once a month all through last year, plus I have a decent pond in my garden with frogs, toads, several newts (endangered here), and plenty of insect life, but I’ve never seen anything like these monsters. They were about 30mm long when they straightened out, which was only when they were swimming (they swim by moving their legs, rather than “jet propulsion”). They sat still in the arched pose in the photo’s until a tadpole came past, then latched onto it and killed it with their pincers. In the photo’s the pincers look a bit like feelers, but in reality they were curved, hard and obviously sharp killing instruments. There are all sorts of pond-skaters, water-boatmen, and general creepy-crawlies in the pond, but these 3 were a lot bigger than anything else, and only interested in killing tadpoles. They seem to have 6 legs, which might be some help, and a couple of small “spikes” on the tail (no gills). The light was terrible for photography, but they were basically green with slightly brown heads. We’ve had dragonfly, damsels, cranes, midges, and just about everything else that flies on the site (bats are my “thing”, and we’ve got those as well), and we’ve also got frogs, toads, a possible newt, lizards, slow-worm, mice, owls, a fox, and deer (which do a lot of damage to the trees if we don’t keep on top of them). We do like nature, in all it’s forms, but the rate these things were eating the tadpoles was quite alarming, so unless they’re something interesting I’ll have to either splat them or at least section off one part of the pond, or we’ll have no tadpoles left. Hope you can help.
Thanks,
Kev.

Hi Kev,
What a wonderful letter. We just posted another photo of a Water Tiger from Northern California. These are the predatory larvae of the Predaceous Diving Beetles in the genus Dytiscus, and they have a voracious appetite. Eric Eaton wrote in with this addition: “I agree the one with the tadpole is a dytiscid, but I’d be hesitant to assign a genus to it. I really think anyone is doing great just getting immatures (and usually adults, too) to the family level! Nice work.”

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What's That Bug? does not endorse extermination
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