The Floranian Blood Flies were a species of a small, yet aggressive form of red insects native to Florana, with a creature similar to it on Daxx. They had a very short attack distance, stabbing at Ratchet with their abdomens and then momentarily retreating. They were usually found in swarms, which more than make up for being individually weak.
The easiest strategy against a large swam of Bloodflies is to use an Area of Effect weapon (i.e. The Nitro Launcheror the Plasma Whip) to either take them out from a long distance, or to protect Ratchet from getting surrounded.