Insects and their Allies  

Trichoptera: caddisflies

Caddisflies are related to Lepidoptera and resemble small hairy moths, but their wings are covered in dense hairs rather than scales and they lack the typical curled proboscis of most moths and butterflies. They are mostly dull-coloured and range in size from 2-40 millimetres in body length. Caddisflies are recognisable by the following features:

Stenopsychodes species
Stenopsychodes species

  • Elongate body
  • 2 pairs of membranous wings that are of differing size
  • Wings covered in fine hairs. Wings form a roof over the abdomen when at rest
  • Reduced mouthparts

Life Cycle
Caddisflies mate during flight and one female can lay up to several hundred eggs. Eggs are enclosed in a gelatinous mass either on or near the water. The larvae are aquatic and have a sclerotised head and thorax and well developed legs. They have a soft body, which they sheath in a casing made from silk that they cover in various materials such as sand or plant debris to provide protection and camouflage. Caddisfly larvae usually develop through 6-7 instars and as they grow more material is added to the front of the protective casing. Pupation takes place underwater within the larval case or in a pupal case made from silk. Most of the life cycle of caddisflies is spent in the larval stage and the adults are generally short lived.

Leptoceridae larval species
Leptoceridae larval species

Adult caddisflies do not feed but the larvae have a wide variety of feeding methods and diets. The larvae may be either herbivorous or predatory. Many feed on various plant materials both living and dead, some feed on algae and others pierce plants sucking out the phloem or xylem. Others filter organic particles from the surrounding water or scrape it off submerged rocks and plants. The predatory species feed mainly on insects with some spinning silken nets to capture prey.

Ethochorema brunneum
Ethochorema brunneum

Adults are predominately found near water bodies, as their young are aquatic. Although there is one species in Australia that has terrestrial larvae. The adults are nocturnal and can sometimes be found resting on tree trunks by streams and lakes during the day. The larvae live in almost all types of freshwater habitats and a few species even inhabit saline waters and marine environments. Water conditions are important to different caddisfly species. Parameters such as oxygen, temperature, chemicals and particulate matter in the water often directly correspond to the presence or absence of certain species in an area. As such caddisfly larvae are sometimes used as environmental indicators of water quality in these areas.