Question
I have a 1000gal pond.  I was doing my Spring cleanup and I had the carbon and filter may pulled out for a few minutes.  When I went to put it all back together there were thousands of tiny green worms coming out of the mesh bag that holds carbon and there was more at the bottom of the filter.  I tried to spray them with the hose and it didn't seem to bother them.  Do you know what these are?  How can I kill them in the filter?  Can humans get them?  Thanks so much for any info. They are really disgusting, esp. since there's so many of them.

Answer
They were green?  Most "worms" in the filter are in fact insect larvae.  Red ones are bloodworms which are midge larvae.  Some midge large are more gray and some can even be green.  There can also be caddisfly or other larvae in the filter.  The good news is that they are not any harm to you or the pond animals.  You can't "get them."  They just want to live in the dark and eat the pond debris so they are actually helping the pond's health.  You can squirt some off but otherwise can't kill them all without using poisons which would also harm your fish, etc.  The Bt bacteria sold as mosquito dunks and liquids kills some fly larvae but not all insect larvae.  So, adding Bt bacteria may kill them.  Personally, I consider the insect life part of the pond and try to protect them but don't fret if I flush some off while cleaning.  Now, if the "green worms" had their mouths affixed to surfaces (sucked on), those would be leeches.  Leeches are actual worms.  The leeches in filter (I have plenty) are not parasitic; they live on debris.  So, they are also nothing to worry about.  I cleaned my smaller ponds out today and saw plenty of those.

Good luck with your pond!