Bloodworms are not worms.   This is the common name for the larvae of a species of midge.  They are aquatic only during this life stage.  The name comes from the color of the larvae.  The color is a result of hemoglobin.  They are members of the family Chironomidae, non-biting midges.  These are the most abundant midges of all the midges. 

 

These larvae are harvested from hypersaline lakes in Ukraine where they thrive in the bottom of the lakes and consume organic matter.  There are very few predators for them.  They are widely fed to tropical fish as a “treat”.   In the wild they are preyed upon by fish and a myriad of other aquatic organisms.