Caddisfly

Limnephilus sp.

An underwater mason who builds with grains of sand

The caddisfly looks like a small, grayish-brown moth, its wings covered in fine hairs rather than scales — exactly where the order name Trichoptera ('hairy wing') comes from. The larva, called a caddisworm, lives in streams; most species spin silk to bind sand and twigs into a portable case and crawl inside it.

Key figures

Wingspan

About 40–55 mm (running larger in the horned-caddisfly group)

Life cycle

1–2 generations a year, overwintering as larvae; adults live a few weeks

Habitat

Larvae live under stones in cool streams; adults swarm along stream banks in the evening

Diet

Larvae filter-feed on algae and detritus; adult mouthparts are reduced to lapping water only

Case-building

Larvae spin silk to bind sand and stone into a case; some groups instead spin nets to filter food

Pupation

A mature larva seals its case and pupates underwater, breaking through the water's surface when it emerges

Life cycle

Egg (laid on the water surface or nearby) → Larva (caddisworm, aquatic) → Pupa (underwater cocoon chamber) → Adult

Ecological role

Caddisfly larvae filter-feed on detritus and algae in streams, drawing organic matter washed down from upstream back into the food chain; they are also a staple food for fish, and the artificial 'wet flies' tied by anglers mostly imitate them.

Did you know

Caddisworms are picky about oxygen and pollution; checking a stream's health, agencies count caddisfly, mayfly, and stonefly larvae on the bed — the EPT index, where a higher count means cleaner water.

Range

Mountain streams throughout China; widespread across temperate East Asia

Status

Common, though it quickly disappears from stream stretches with degraded water quality

Anatomy

• Hairy Wing — Wings densely covered in fine hairs, folded roof-like over the back at rest
• Antenna — Thread-like, as long as the body or longer, held forward and together at rest
• Maxillary Palp — Segmented and bent like a small whip, an important feature (maxillary palp) for identifying caddisfly families
• Compound Eye — Takes flight at dusk, still able to guide the streamside mating swarm in low light
• Thorax — Raised on top with small tubercles, bearing both pairs of wings and the slender legs
• Abdomen — Soft and slender; females often dip it against the water's surface repeatedly while laying eggs

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