Adult stoneflies are brown, black, green, or yellow and are usually marked with distinctive light or dark patterns. Their bodies are somewhat flattened with legs outstretched to the sides. They range in length from 0.19 to 1.97 inches (5 to 50 millimeters). The broad head is equipped with compound eyes that have more than one lens each, with simple eyes with only one lens, and with chewing mouthparts that are directed forward. The antennae (an-TEH-nee), or sense organs, are long and threadlike. Nearly all species have four fully developed wings that are held flat over the back. At rest the wings are usually as long or longer than the abdomen. A few species of stoneflies are completely wingless or have short wings that are not capable of flight. The hind wings are folded lengthwise when held at rest under the forewings. The abdomen is ten-segmented and is tipped with a pair of short to long, threadlike projections.
The larvae (LAR-vee), or young form of the animal, may or may not closely resemble the adults. Like the adults, their bodies are flattened, with short, sometimes pointed wing pads and outstretched legs. Plant feeders and scavengers (SKAE-vihn-jers), or animals that eat decaying matter, have specialized mouthparts that allow then to scrape algae off rocks, collect fine bits of plant food, shred living and dead leaves into smaller pieces, or chew chunks from leaves. Predatory larvae have sharpened mouthparts that help them to grasp and hold their prey, or animals hunted for food. The larvae may have simple or feathery gills located on their head, thorax or midsection, and abdomen. They always have a pair of segmented projections on the tip of their abdomen.
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