Bloodworms

Interesting, i found a group of those in a park near my house in san josé, costa rica. Now i know what they are!

Interesting and sounds logical! I've added your suggestion as the name. Thanks a lot Mark!

There's many species looking slightly different. It might be difficult to find which one yours is. That's why I suggested a family level ID only. You could research which species are in your area and you might get lucky. :-) The ones I found were in a totally dry bird bath. I suspect the larvae gather together when a place goes dry in an attempt to keep moisture around them.

Additionally, Wikipedia says "Larval stages of Chironomidae can be found in almost any aquatic or semiaquatic habitat (...)". These were just on a dry floor. That seems rather odd?

Added the video!

Mark, thanks for the suggestion! They do look similar. However, it seems like these have a black head, while the images I find of bloodworm larvae don't seem to have that. Or would that just be some local variation?

'bloodworms' (sorry)

heh heh... search 'blodworms' it's a good read