As the larvae of the butterflies and moths, most caterpillars possess highly terrestrial life histories. However, a rare few experience their larval lives underwater in the rocky substrates of streams and rivers or among the aquatic vascular plants of streams, lakes, or ponds. Here, herbaceous aquatic caterpillars often exhibit the same preference for host plants as their terrestrial counterparts, using their chewing mouthparts to graze microflora or feed on certain species of aquatic vascular plants. Like land-dwelling caterpillars, aquatic caterpillars are distinguished by their elongated, somewhat cylindrical bodies, distinctive heads with at most simple eye spots, three pairs of legs on the thorax, and short pairs of prolegs along the bottom of the abdomen.
Most moths are terrestrial, however a few of the caterpillars of the family Crambidae are truly aquatic (about 740 species worldwide, 160 in North America). They are holometabolous, meaning they have egg, larval, pupal, and adult stages. They can be found in a variety of lentic and lotic habitats. Most larvae feed on floating plants or algae on rock surfaces. Often, first instar larvae are hydrophilic (water-loving) and absorb oxygen directly from the water. As the larvae become larger some species become hydrophobic (water-resistant) with a layer of air held against the body. This is advantageous, as oxygen diffuses more rapidly through air than water. Similar to the closely related Trichoptera (caddisflies), some species make cases or tents out of plant material and silk. They often have a close relationship with a host plant on which they both live and feed; these plant feeders often cover themselves with pieces of leaf or they burrow in the stem. The algal-feeding species of genus Petrophila live in streams and spin a silk tent on a rock or other solid substrate from beneath which they graze on the algae. The caterpillars pupate in or beneath the plant or silk material, and emerge as terrestrial moths.
+ Expanded Character List
Caterpillars with wings and wing pads absent. Eye spots usually present, but compound eyes absent. Short segmented legs present on thorax, not as long as abdomen. Underside of abdomen with several pairs of prolegs (fleshy nubs) with tiny hooks.
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