I've got these in a water tub too. So I'm curious to know what they are and where they come from.

hi they could be daphne /water fleas. water boatmen. i dont think any will harm plants. so carry on as normal.good luck.

if they are water boatmen look closely and you can see how they get their name.they can give you a little nip .

What, you mean they really are little men in boats ;o)

Are they mosquito larvae?

hi sheila water boatmen look like some one rowing a boat so no you daft sod julien no they they are not mossie larvae daphne are often found in a cows water trough that like a big bath sheila.good luck.

Mosquito larvae have big, roundish "heads", and hang by their tails from the water surface, until they are disturbed--often by the shadow of someone trying to look at them--when they swim down into the water with a shrimp-like threshing of their tails. If you stand still long enough, they will return to the surface.
Water boatmen are oval, beetle-like bugs that lay on their backs and swim around under the water with their long, oar-like hind legs. Many species eat mosquito larvae.
Daphne, aka "water fleas", are flattened like fleas, and swim around in a jerky motion by threshing their legs.
Tadpole shrimp look and swim much like tadpoles, but under a magnifying glass are revealed as a tiny crustacean, like the Daphne.
Except for the mossies, which grow up to bite, all are harmless to people, and plants will just say "Yum!" if they are poured out on the roots--including the mossies!

Mosquito, I have them as well.

Add a small drop of liquid soap (Sunlight or Fairy) to the water. They dont like baths and will go away.

They may be woolie bears washed from your guttering. Check the gutters are clean.

I agree, mosquito larvae. You can stop them breathing at the surface of the water by adding one tiny drop of washing up liquid to the water so they can't use the surface tension effect at the surface, or add a drop or two of cooking oil to form a film on the surface of the water that they can't get their breathing tube through. Both of these get rid of the larvae.

..or pop a goldfish in there to eat them all!