The Sialoidea These insects are often of large size and eye catching in both form and colour. They are a primative group and have only a small number of genera and species. They have a worldwide distribution although not a continuous one. Eggs are usually laid in close proximity to water on stones and vegetation, laid in cohesive masses with egg number varying according to species. Sialis will oviposit masses from two hundred to five hundred eggs whilst Corydalis can lay two to three thousand.
Eggs are cylindrical with rounded ends and dark brown.
The larvae crawl to the water after hatching and will live in any waters from slow moving canals to fast running streams depending of a particular species preference. Larvae of the family Corydalidae have the ability to stay alive for many weeks under stones in dry stream and river beds. Mouthparts of all larvae are well developed for killing and chewing small aquatic insects, worms etc. Larvae often display abdominal appendages which are accessory tracheal gills, these take on many forms and are attached to what appear as seven pairs of extra legs running along the abdomen in Sialis to seven spongy tufts attached ventrally to the abdomen in Neuromus . These insect are entirely terrestrial in habit and quite specilized.