carnivorous water boat men?

[gwynleg]

I had lots and lots of tadpoles but today - very few. I saw a waterboat man thing appearing to have hold of a tadpole tail and swimming with it (certainly looked that way round). Could this be killing my tadpoles?
I am so sad - I was really looking forward to lots of frogs!!

[Paulines7]

It seems they do eat tadpoles as well as fish. 
See: http://www.bbc.co.uk/nature/wildfacts/factfiles/428.shtml

[gwynleg]

Thanks for that info Pauline - thats very depressing though - I want some tadpoles and frogs!! I see that frogs eat waterboat men but I have to get the frogs first!!

[queenbee]

Tadpoles eat water boatmen and visa versa, this balances the eco system in a pond. After losing my last two twenty year old Koi to a fox I decided not to restock, the tadpole population last year was phenomenal, we had to brush the thumbnail sized frogs off the lawn before we mowed it, everytime I weeded the garden the froglets would be jumping around. This year is no exception. I love frogs but draw the line at them jumping on my hands. My frogs are also averse to eating slugs and snails as I am inundated with the b------rs. Next year I shall be taking a few bucketfuls of frogspawn to the local canal as my garden is overrun.   

[amphibian]

It is normal for tadpole populations to drop as they mature, they eat each other.