Arthropods 12

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Southern California Arthropods (Mostly) #12: Caddisflies (Order Trichoptera)
© W.P. Armstrong 15 April 2009
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Caddisflies are aquatic in their immature (larval) stage. The larvae are bottom dwellers and construct tube-like cases made from silk, with bits of leaves, twigs, sand grains, pebbles, or other objects incorporated into the case to give the larvae protection and camouflage. The shape and type of construction material depends on the particular species. Adult caddisflies resemble small moths, except they lack the coiled, sucking mouthparts of moths, and they have hairs on their wings instead of scales. In fact, the order Trichoptera refers to "hair-wing" insects. Like moths, caddisflies are nocturnal and are often attracted to lights.

Two species of caddisfly larvae (family Limnephilidae) in their protective cases. One is made from leaves and the other from grains of sand. The case made of sand grains is 27 mm long. Both were collected in Little Mermaids Canyon at junction with West Fork of the San Gabriel River, Los Angeles County, California (1965).

Beware Of The Case-Making Clothes Moth
This Is Not A Caddisfly! It Is A True Moth

This is not a caddisfly! It was found on the bathroom floor at Wayne's Word. It is a case-making clothes moth (Tinea pellionella) in the family Tineidae. The brown-headed larva spins a silken case that is open at both ends. The case in the above image is covered with fine sand and debris, and superficially resembles a caddisfly case. The flattened case is about 10-11 mm long (3/8 to 1/2 inch). When crawling, the larva's head, thorax, and three pairs of legs protrude out of the case, and drag it along. According to Internet sources, the larva feeds on a variety of material, including hair, fur, silk, felt, feathers, woolen clothing, upholstered furniture and carpets. It apparently prefers darkness and soiled clothing, and is not fond of synthetic fabrics, such as nylon and polyesters. See the following image to see what it ate in a simple test performed at Wayne's Word. Photo taken with Sony T-9.

This clothes moth larva was presented with seven potential food choices: A. Black dyed silk, B. Heavy raw silk, C. Flax flake cereal, D. Linen, E. Cotton, F. Red wool, and G. Oatmeal cereal. After crawling to several different textile samples, the larva selected the Quaker oatmeal. It proceeded to feed on the oatmeal with its head protruding out of its protective case (yellow arrow). Although it is called a clothes moth, it did not seem interested in the textile samples. Photo taken with Nikon D-90 and SB-600 flash in a dimly lit room. Under prolonged bright light using photoflood lamps and a light box, the larva withdrew into its case.

Close-up view of clothes moth larva on a piece of red wool.


  1. Evans, A.V. 2007. Field Guide to Insects and Spiders of North America. Sterling Publishing Co., Inc. New York, New York.

  2. Hogue, C.L. 1993. Insects of the Los Angeles Basin. Natural History Museum of Los Angeles County.

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