The New Zealand hydrobiosid caddis larvae have pincers on their forelegs. Costachorema larvae are often first recognised by the extensive black pigmentation on the top of the head. Under the prothorax (first segment behind the head) between the forelegs is a prosternal plate that is much wider than long.
Costachorema larvae are common in stony streams and rivers, in bush covered and farmland areas.
They are predators, feeding on other stream invertebrates.
An abundance of Costachorema larvae indicates good water quality, particularly where mayfly and stonefly nymphs are also abundant. They have tolerance values of 7 (hard bottom sites) and 7.2 (soft bottom sites).