Water penny larvae feed on periphyton, the thin layer of algae and micro-organisms that forms on stones and other objects in moving freshwater. Larvae of some species seem to be attracted to each other, but some are solitary and it is rare to find more than one. This helps them keep their place in streams, and not be washed into the water. Water penny larvae tend to move away from light, cling to whatever they touch, and move into any water current they encounter. gonochoric/gonochoristic/dioecious (sexes separate).Believed to all be sexual dioecious species (each individual either male or female), with internal fertilization. Probably semelparous, adults only live a few weeks. Psephenus herricki females lay hundreds or thousands of small, bright yellow eggs on submerged and emergent objects in stream riffles with fast current. Reproduction information only known for one or a few species. Pupation is completed inside the larval skin. Some species create an air-filled chamber under water, but most pupate on land, in moist soil. When read to transform, larvae small chamber where they enter the pupal stage and metamorphose into an adult. If the warm season is short, they may need more than one year to complete the larval stage. In this stage they grow and molt several times during warm months. They cling to gravel and other hard debris in the water, grazing on the algae and other micro-organisms that grow there. Aquatic larvae hatch from the eggs and drop or crawl into the water. ( Brown, 1991 McCafferty, 1983 White and Brigham, 1996 Wichard, et al., 2002)įemale water penny beetles lay their eggs above or at the edge of the stream or shore habitat where their larvae will live. In the rest of the family, pupae and adults are air-breathers, with functional spiracles. The genus Psephenoides is more fully aquatic, neither larvae nor pupae have functional spiracles, and both stages have gills. Most also have filamentous gills that extract oxygen from the water, either paired structures on abdomenal sterna, or a single caudal structure near the anus. They have a few functional spiracles for air breathing. Most species in this family have amphipneustic larvae: they can extract oxygen both from air and directly from the water. Larvae have clawed legs for clinging to rocks in moving water, and chewing mouthparts for scraping food off of rock and other hard substrate.Īdults are dark-colored, 4-6 mm long, with somewhat flattened bodies, short thread-like antennae, and mandibles not visible from above.
#Riffle beetle larvae plus
This flat round shape, plus their brownish color, earns them the name "water pennies". They dorso-ventrally flattened, with expansions of the dorsal plates that extend out so far that they are oblong or nearly round when viewed from above - the head and legs completely covered. Larvae are 3-10 mm long, ranging in color from pale amber to nearly black (usually matching the substrate) and have a distinctive shape. ( Brown, 1991 McCafferty, 1983 White and Brigham, 1996)
Adults are often found on the underside of logs and other objects overhanging streams. Most pupae and all adults are air-breathing, but stay near the water. They are most often found in fast-moving streams, especially riffle beds, but some species are found on rocky lake shores with wave action. Psephenid larvae cling to hard substrates (rocks, woody debris) in well-oxygenated water. Members of the Psephenidae are found on all continents except Antarctica. ( Brown, 1991 Lee, et al., 2007 Shepard, 2002) Geographic Range There are only about 263 species in 31 genera are known (Lee et alia, 2007) but this family has not received intensive study, and there are probably more species still undescribed. The classification of the family is uncertain, some authorities recognize some subgroups as separate families. This small family of beetles gets its common name ("water pennies") from the unusual shape of the larvae, which have widely expanded dorsal plates that give the animals a flat round shape, like a coin.
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