4" red worm in my tank - what is it, where did it come from, & should I worry?

[Crepe]

to rule out the bloodworm question, bloodworms are just mosquito larvae and do not get long like that

Glassworms are white mosquito larvae. Blood worms are the larval stages of midges. Different things. Bloodworms inhabit similar environments as tubifex though.

 

[Mark1092]

Maybe it came in with the water as a near-invisible egg or whatever then grew?

 

[Bigballs]

Ewwww

 

[hbeth82]

I doubt it came in with the water since all of my water goes through an RO+DI filter, but it's possible. I do know that from now on I'm going to be paranoid about siphoning out the gravel!