Please identify worm wriggling in tank water from my description :(

[On_a_dishy]

I had a white/grey worm wriggling in my tank this morning. It has now broken up and gone through the filter. It was the size of a sizeable bloodworm, and wriggled like one too. I last fed my fish live bloodworms about 5 days ago, and they never live for that long, so I don't think it was that. I have footage, but can't work out how to attach it, and when I take a screenshot it doesn't really offer anything of use to you as it's so blurry!
I can get to my LFS for flubendazole later today if necessary.
The tank is very new but I introduced new gouramis to it yesterday, and new guppies a few days before that.

 

[On_a_dishy]

It was an insect larvae! I can't remember which fly the LFS person said, but it was a larvae thrashing around! It eventually died and got sucked into the filter, so that'll be a treat for another day.

 

[Sgooosh]

It was an insect larvae! I can't remember which fly the LFS person said, but it was a larvae thrashing around! It eventually died and got sucked into the filter, so that'll be a treat for another day.

poor little bugger

 

[Sgooosh]

It was an insect larvae! I can't remember which fly the LFS person said, but it was a larvae thrashing around! It eventually died and got sucked into the filter, so that'll be a treat for another day.

clean it out or it will cause AmmoniaSpike

 

[On_a_dishy]

Nooo! I've just achieved cycling paradise! Right, that's at the top of the "To do" list - thank you.