What are these!?

Set up a plastic container outside, using it for growing duckweed and some other floating plants. Noticed these worm-like things in there. What are they, and how can I get rid of them?

Looks like mosquito larvae.

I agree.

Crispii wins, they are mozzie larvae. Use a fine mesh fish net and scoop them out, rinse under tap water then add to aquarium. Fish will go nuts over them.

I agree. They are mosquito larvae.

Fish love to eat them.

If I put them in a tank, what happens to the ones that don’t get eaten? Will they live? And will the ones in the container grow?

Any mozzie larvae that don't get eaten will turn into adult mozzies.

They have a couple of stages in their life cycle.
1) The egg, small black dust that floats on surface of water.
2) Baby/ larvae, start out small (2mm) and grow bigger (8-10mm). The things in the picture in your first post are baby mozzies in their larvae stage.
3) Pupae stage where they turn into a comma shape.
4) After a few days as pupae they hatch and turn into adult mozzies.

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If you get too many mozzie larvae, you can put them in ice cube trays with a small amount of water and freeze them. Then put the frozen blocks in a ziplock bag and keep frozen. Use them when there are no more mozzie larvae outside.

What do I do about the ones already in the tank? I don’t think I’d be able to find them, and don’t want to end up with adults. Will tetras be able to hunt them down?

Goldfishgirl35 said:

What do I do about the ones already in the tank? I don’t think I’d be able to find them, and don’t want to end up with adults. Will tetras be able to hunt them down?

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Nothing. The fish will eat them.

Mosquito larvae. Fish should munch on them

I feed my tetras larvae everyday and yet to have a mosquito show up. They really love them and if one gets away he will not last long, they have to go up for air and the fish will eat them. then.