Wilderness Underfoot: The young caddisfly's perfect camouflage

StoryImage( ‘/Images/Story//Auto-img-112429773629346.jpg’, ”, ‘Underwater RVs – Two different species of Caddisfly larvae, each with its own preferred building material. The upper caddisfly builds its case of sand, while the lower caddisfly uses plant debris.’);
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Caddisfly offspring often build protective cases of sand, dead plants and other debris

If you’re an inch-long, wormlike creature in a stream where fishes and larger critters are hungrily searching for their next meal, what better disguise than an outer shell made of sand or dead vegetation? It blends in with the surroundings and, even if it is seen, it doesn’t look particularly appetizing. This is the trick of camouflage used by the aquatic offspring of many caddisfly species.

Caddisflies are insects closely related to moths. The adult caddisflies are easily mistaken for moths with drab coloring. When at rest, they hold their wings in a familiar tent-like fashion of certain moths. And like moths, most adult caddisflies are night flyers.

It’s easy to collect and observe the adults by simply turning on an outdoor light at night, especially if you’re anywhere near a gently flowing stream or river. You won’t have an easy time distinguishing the different species, however, even with a good field guide; there are 21 caddisfly families and more than 1,400 species in North America, alone. They are the largest order of aquatic insects.

The offspring (“larvae”) of both moths and caddisflies possess silk glands in their lower lips. This silk is used by young caddisflies of certain species to string together bits and pieces of debris to make their protective cases. Each caddisfly species has its own preferences for building materials. Some use only plant debris, which they cut into pieces with their mouthparts. Others use sand and rock. And still others will mix a hodgepodge of building materials. Although these cases appear to be a heavy burden, they are actually buoyant and nearly weightless underwater.

Most of the case-building caddisflies are plant eaters or scavengers, while free-roaming caddisflies—those that don’t build cases—are generally predatory. Free-roaming caddisflies often use their silk to cast nets underwater and entrap other creatures.

Eggs are laid in water or attached to rocks and aquatic plants. The larvae may spend several months to a full year under water before they go through metamorphosis and turn into pupae. The pupae are also aquatic. Adults later emerge from the pupae and take to the skies. As adults, these poor creatures are usually incapable of eating. They spend their short adult lives mating and laying eggs, living off the energy stored from their larval stage.

From the August 17-23, 2005, issue

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