They are blood red in colour because they have haemoglobin in their blood. Mammals, including people, have haemoglobin in their blood also. Haemoglobin holds much oxygen and therefore bloodworms can live in water that is low in oxygen. Bloodworms eat vegetation found in the water. They stick to plants, rocks and submerged twigs, often in large numbers.
Some bloodworms live in tubes that they build from sediment, sand or small stones, and plant debris.
They stick these bits together with a sticky secretion. Like the mosquito 'tumbler', the pupa stage of the true midge is active. The midge pupa is 0.48 cm long. The adult bloodworm is a midge, about 0.5 cm long, that resembles a mosquito except that the males have long feathery antennae and the back legs are much longer. Unlike mosquitoes, most true midges do not bite but instead live on plant juices.