Black worms dropping from my pipes?

I have a pipe running above in my kitchen, near the stove and sink. Every now and then i find black tiny worms as small as 5mm, wriggling. I tried to use white plaster to cover up the white metal pipes in case there is a tiny leakage, but they seem to come back with more dropping down. They are certainly not mosquito babies. But what the hell are they? And how do I get rid of them?