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Caddisflies: Freshwater Species of the Week

  They are little known by the general public, but caddisflies are an ancient group of aquatic insects that are important indicators of ecological health. For this week’s Freshwater Species of the Week, we interviewed caddisfly expert Kjell Arne Johanson, a professor and head of the entomology department at the Swedish Museum of Natural History....

A male caddisfly (Limnephilus centralis); caddisflies are a large and important group of freshwater insects that have much to teach us. Photo: Kjell Arne Johanson


freshwater species of the weekThey are little known by the general public, but caddisflies are an ancient group of aquatic insects that are important indicators of ecological health. For this week’s Freshwater Species of the Week, we interviewed caddisfly expert Kjell Arne Johanson, a professor and head of the entomology department at the Swedish Museum of Natural History.

Johanson recently received a grant from National Geographic to study the biodiverse but little known caddisflies in Bolivia. Working with colleagues at the Museo de Historia Natural d’Orbigny in Cochabamba, Bolivia, and the Natural History Museum in Gothenburg, Sweden, Johanson hopes to better understand caddisflies and their freshwater ecosystems, many of which now face development pressure.

Most related to moths and butterflies, caddisflies are also called sedge-flies or rail-flies, and there are some 14,000 described species. The small, moth-like insects have two pairs of hairy membranous wings. The larvae are aquatic and can be found in many lakes, rivers, springs, and ponds.

Many caddisfly larvae spin protective cases out of silk that incorporate bits of sand, gravel, twigs, or other material.

Water Currents: How did you get started studying caddisflies?

Johanson: I’ve been a research entomologist at the Swedish Museum of Natural History for 12 years. My masters’ thesis was on moist forest in Tanzania, East Africa. It was in a rainforest reserve never touched by man, with a stream running through a very beautiful forest.

We set traps along the stream and collected a huge number of undescribed species of caddisfly. It was a great start for me. I was engaged in Trichoptera systematics [classifying the order that contains caddisflies], and I never stopped. Over time I expanded my interests both geographically and in topic, becoming more molecular based in my approach.

Polycentropodidae - Polycentropus flavomaculatus male
A Polycentropus flavomaculatus male caddisfly. The insects are often considered indicator species. Photo: Kjell Arne Johanson


Can you tell us about your recent work?

My recent research is about classification and the age of caddisflies as a whole. My PhD student and I have almost completed a paper on phylogenetic evolution of Trichoptera, with molecular dating of families in the order, with very nice results. One of the interesting things we’ve found is that it appears that diversification of caddisflies was made on production of larval cases.

Larvae produce cases that they hide within, and many produce a current of water inside by undulating their bodies like a snake, so they can get more oxygen from water. That is possibly an important factor for getting established in stagnant water. It also helps them hide from predators.

There are more caddisfly species than the sum of the other three major orders of aquatic insects, the dragonflies, stoneflies, and mayflies. We try to explain that by production of these larval cases. We also found that Trichoptera is around 234 million years old; that is the splitting point between caddisflies and butterflies and moths. There had been some speculations before, but there had been some large intervals. We used molecular methods to pinpoint it.

Aren’t caddisflies important indicator species, signaling to scientists that an ecosystem has problems?

I’m not so much into indicator work but it has been demonstrated that within many groups there are species that are more tolerant of pollution and those that are less tolerant, not only to pollution but also to water level changes. Some survive downstream of dams very well, others are totally excluded.

Caddisfly larvae live for around 11 months before they pupate, so they accumulate pollution from the water and are good for extracting chemicals dating back several months.  Of course, pollution will affect larvae and they will die if some pollutants get too high. Some species react in different ways.

Leptoceridae - Mystacides azurea female (left) and male
Mystacides azurea female (left) and male. Photo: Kjell Arne Johanson


Anabolia nervosa larva 2
Caddisfly larvae often make homes out of silk and particles they scavenge. Pictured is an Anabolia nervosa larva. Photo: Kjell Arne Johanson


Are they important ecologically?

They have been able to adapt to many different kinds of water systems and they are very important for water ecosystems and above the water. They are a food resource for many kinds of organisms, including bats, birds, amphibians, fish, and other insects, such as diving beetles and dragonfly larvae. By occupying so many different niches they are available in far higher degree than other organisms.

We should try to save as many microhabitats as possible because there are many species that are dependent on them. There might be quite many species within a small area, and that diversity should be saved in order to keep ecosystems intact.

Anything else we should know about caddisflies?

They are quite beautiful. Although many are gray-brownish there are a lot of species that are more or less colorful, reminding of the colorful moths. They are fascinating in many respects. They build these larval cases from different kinds of material, and they use what they find. There are species-specific requirements, but they will try to build cases from what they have around them.

In East Asia some larvae are given gemstones like gold pieces or pearls, which they glue together with silk to make their tubular cases. After the larvae hatch these cases can be used as necklaces; they can be quite beautiful.


Brian Clark Howard is an Environment Writer and Editor at National Geographic News. He previously served as an editor for and E/The Environmental Magazine, and has written for,,, Yahoo!, MSN, Miller-McCune and elsewhere. He is the co-author of six books, including Geothermal HVACGreen Lighting and Build Your Own Small Wind Power System.

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