Bloodworm (Chironomus tetans) head, coloured scanning electron micrograph (SEM). The bloodworm is the freshwater larva of a midge. It is able to live in stagnant water and muddy pools because the haemoglobin in its body helps to absorb what little oxygen there is. It is also this haemoglobin which leads to the red colour from which the larva gains its common name. It is used in fishing as bait. Magnification: x500 when printed at 10 centimetres wide.