In message , K
writes
Robert writes
In message 8, Tom
Gardner writes
Robert wrote in :

It is possible that you have a large number of planarians in the pond.
They are small, leech like, flatworms that will steadily munch their way
through frogspawn.

No idea, but I'll have a look. Thanks for a useful starting point.

These invertebrates arrived in our pond some years
ago and removed all the embryos from the clumps of spawn for a couple of
years. We now watch out for the spawn to appear, remove it to a couple
of large containers and return the tadpoles to the pond when they have
hatched - so that the newts have got something to eat :-)

That was last year's experience

But then I've got a soft spot for newts anyway

The worms are very small ~ 10mm long and 1mm wide, brown to black in
colour. One way to check is to drop a small piece of raw chicken into
the pond where you can see it - if the flatworms are present they will
appear within minutes and head for the meat.

Just how many do you need for it to be a problem? We have them in all
our ponds, at the level where turning over any stone will reveal about
4 or 5 of them. But the effect on frogspawn is unnoticeably tiny (the
spawn immediately after hatching is a writhing mass of mini-tadpoles)
and we produce baby newts in good numbers.

Unfortunately we have hundreds of them in a smallish pond. We mucked
out the pond three years ago in an effort to get rid of them but to no
avail. I will try and get an image of one later this week and put it
online.

--
Robert