When a bloodworm bites you the bloodworm injects a venom into your body which can cause some people an allergic reaction which requires medical attention and a stay in the hospital.
There have been bloodworm collectors who have gotten bitten by bloodworms and they were injected with the venom which caused an allergic reaction that could've been deadly if they hadn't went to the hospital or got medical attention soon enough.
If you handle bloodworms you should wear some thick gloves that the bloodworm should not be able to bite through.
The bite from a bloodworm will also be painful and you'll usually know within a few minutes that you're having an allergic reaction to the bloodworm venom.
Bloodworms feed by extending a large proboscis that bears four hollow jaws are connected to glands that supply venom which they use to kill their prey, and their bite is painful even to a human.
Bloodworms are also prey to other worms and even bottom feeding fish and crustaceans, and by gulls.