Harrisius is one of the Chironomini subfamily of the Chironomidae. Like other chironomids the general body form is worm-like, but with a distinct head, and with paired prolegs under the head and at the end of the abdomen. In Harrisius the head is wide and flattened, and there are distinctive tentacle-like tubules extending backwards from the end of the abdomen.
Harrisius larvae are often found in decomposing wood lying in bush covered or farmland streams.
They burrow into, and feed on decomposing wood.
An abundance of Harrisius is likely to reflect an abundance of decomposing wood in the sample, which may reflect good riparian vegetation. They have mid range tolerance values of 6 (hard bottom sites) and 4.7 (soft bottom sites).