Coleoptera

Introduction

Beetles. The largest order with over 130 families and 350,000 species worldwide or about one-third of all described animal species. About 25,000 species occur in North America, north of Mexico, but only about 1200 of these are purely aquatic. Many additional species are semiaquatic. Endopterygota, holometabolous.

Recognition

Larvae without external wingpads, thoracic legs usually present, no abdominal prolegs, antennae with more than one segment, not a neuropteran/megalopteran. Adults with chewing mouthparts, fore wings modified into a hard elytra, which covers the hind wings and usually most of the abdomen, antennae with 11 or fewer segments. Pupae are exarate, pads of forewings thickened, antennae with 11 or fewer segments, usually above water.

Life Cycle

Highly variable- most species are univoltine with rapid larval growth during the summer and long-lived adults. Some adults are short-lived, some larvae take nearly a full year to complete their growth, a few take several years. Adults and/or larvae (rarely eggs) overwinter. There are normally 3 to 8 larval instars. The last instar larva usually leaves the water to find a pupation site. Adults emerge and walk or fly to the water. Adults may stridulate to attract mates. Eggs are usually laid in the habitat of the larvae and seldom diapause.

Trophic Roles

All trophic roles are assumed by Coleoptera species. Many species are predacious, some with extra-oral digestion. Species from secondarily aquatic families often feed on aquatic vascular plants.

Communities

Coleoptera species are present in streams of all sizes as well as all types of shallow lentic habitats. The larvae and adults of most species are dependent on atmospheric oxygen, but some respire aquatically or obtain oxygen from submerged vascular plants. Beetle communities are most complex in small, warm, ponds, where the many species are separated by habitat, trophic role, period of activity, and body size. Temporary ponds are often well populated. The open channel of lotic habitats normally has few species, but may have large densities. The beach zone of both lentic and lotic waters may have many specialized species. Adults and larvae normally have the same habitat, but there are notable exceptions.

Economic Importance

Many important terrestrial pests and beneficial predators, some secondarily aquatic families (Chrysomelidae and Curculionidae) can be pests of semiaquatic crops (rice), some terrestrial species are used as fishing fly patterns and as fish bait. Aquatic species are far less consequential to man. Some are eaten by fish, others may eat fish, may help control nuisance organisms, many are good water quality indicators.

Zoogeography

Long-lived, strong flying adults make many species widely distributed. Species in springs are sometimes flightless and more local.

Collecting

The aquatic larvae and adults are usually collected in similar manners. Lotic, open channel species are easily collected by routine benthic samples, some are very small, some may cling strongly to the substrate and to the net. Many lotic species hug the shorelines and are nocturnal, these can be highly aggregated by day. Most aquatic and semiaquatic beetles (except those that favor springs) disperse widely as adults and many are attracted to black lights. Semiaquatic adults can be swept from shoreline vegetation. Lentic species may be collected by rigorously netting up the vegetation and extracting through a Berlese funnel. Large powerful swimmers may avoid most netting attempts. Many species are more vulnerable at night. Species on beaches may be flooded into the water and netted from the surface, but some species run very fast or may even take flight from the surface. Bottle traps can be very effective in vegetation choked ponds.

Rearing

The pupae can be easily reared (if found) until the adults emerge, by keeping them alive is a cool place. Getting the larvae to pupae can be more difficult. The first instar larvae may be reared from eggs. The larvae are generally cannibalistic.

Preservation

Larvae are best fixed in Kahle's solution and stored in 70% ethanol. The adults may be treated similarly, or collected straight into 70-80% ethanol. The adults are best studied dry. They may be pinned or pointed after storage in fluids or they may be killed in a killing jar and pinned or pointed directly.

Taxonomy

The great diversity creates many exceptions for high level taxa. Most aquatic groups are reasonably well known, taxonomicly as adults at the species level. The larvae are much less well known. Both stages are poorly known biologically. Mostly a specialist's group below the family level, except for Elmidae.

Synopsis Of Neartic Families

  1. Suborder Adephaga- The terrestrial Geadephaga and the aquatic Hydradephaga, mostly predacious with chemical defenses. The larval legs have 6 total segments (coxa, trochanter, femur, tibia, tarsus and pretarsus, which consists of 2 claws (1 in Haliplidae), the antennae are 4 segmented (3 in Amphizoidae). The adults have the first abdominal sternite divided by the metacoxae, the hind trochanters are large and offset toward the middle, antennae are normally filiform with 11 segments, the notopleural suture is present, tarsi usually 5-5-5.
    1. Haliplidae- crawling water beetles, herbivorous, widespread in ponds and lakes some prefer streams. The larvae have 1 tarsal claw and do not swim. The swimming adults with the hind coxae expanded into large plates.
    2. Gyrinidae- whirligig beetles, prefer ponds and lakes or the margins and backwaters of streams and rivers. The larvae craw through dense bottom debris, they have lateral gills on the abdomen and 2 pairs of hooks on segment 10. The adults spend much time swimming on the surface, they have the compound eyes divided into dorsal and ventral parts, the antennae is very short and stout.
    3. Noteridae- burrowing water beetles, mainly tropical in hydrophyte choked waters. The larvae are non-swimming and non-tapered with short, fossorial legs and broad mandibles. The swimming adults have the prosternal process wide, flat and abuts on metasternal process.
    4. Dytiscidae- predacious diving beetles, occur in all types of aquatic habitats, most larvae and all adults swim. The larvae are tapered with 8 abdominal segments, with long legs and sickle-shaped mandibles. The adults have the prosternal process acute and indenting into metasternum.
    5. Amphizoidae- trout stream beetles, usually found at stream margins on organic substrates, both larvae and adults crawl and float if dislodged. The larvae have 3 visible antennal segments and the tergites have explanate lateral edges. The adults are 11-16 mm and lack swimming adaptations.
    6. Carabidae- ground beetles, in the broadest sense all Geadephaga, many species occur only on beaches. The larvae are diverse, but without aquatic adaptations (gills or swimming hairs). The adults also lack aquatic adaptations, the terminal antennal segments of nearly all species with fine pubescence, unlike the Hydradephaga.

  2. Suborder Myxophaga- Two families (in the Neartic) of tiny (0.5 - 1.5 mm) aquatic beetles. Larvae with spiracular gills, many species pupate under water. The adults have tarsi 3-3-3 and weakly clubbed antennae of less than 9 segments, notopleural sutures are present, the hind coxae is expanded.
    1. Hydroscaphidae- skiff beetles, mostly tropical in algae mats of shallow streams. The larvae have 2 antennal segments and spiracular gills on the thorax and abdominal segments 1 and 8. The adult antenna has 8 segments with the last segment enlarged, the elytra is short.
    2. Microsporidae minute bog beetles, once Sphaeriidae, larvae and adults occur in interstitial spaces at stream edges. The larvae have 2 visible antennal segments and spiracular gills on abdominal segments 1-8. The adults are oval, shiny, convex dorsally.

  3. Suborder Polyphaga- The majority of Coleoptera. The larval legs have 5 total segments (coxa, trochanter, femur, tibia and tarsungulus, which consist of a single claw, or the legs may be further reduced or absent, antennae have 3 or fewer segments. The adults have the first abdominal sternite not divided by the metacoxae, the hind trochanters are seldom large and offset toward middle, the notopleural suture is usually lacking, the antennae and tarsi formulae are diverse.
    1. Staphylinidae- rove beetles, many species occur only on beaches. The larvae are elongate with sickle-shaped mandibles. The adults are elongate with antennae more-or-less filiform and with the elytra usually very short.
    2. Hydraenidae- minute moss beetles, 1 to 3 mm long algae eaters mostly at water margins, rarely among moss. The larvae have 10 abdominal segments and 5 ocelli on each side. The adults the maxillary palps longer than the antennae, 6 or 7 visible abdominal sterna and antenna with a 5 segmented club.
    3. Hydrophilidae- water scavenger beetles, widespread in many types of aquatic habitats especially warmer ones. The larvae are mainly carnivorous, lightly sclerotized, with 8 abdominal segments, large mandibles, and 6 ocelli on each side. The adults are scavengers with the maxillary palps longer than the antennae, the are 5 visible abdominal sterna, a short antennae of 7-9 segments with a 4 segmented club.
    4. Georyssidae- minute mud-loving beetles, larvae and adults live on sandy to muddy beaches. The larvae are hydrophilid-like, but with 3 segmented legs. The adults are 1-3 mm long, with maxillary palps shorter than the antennae, which has 9 segments and a 3 segmented club, tarsi are 4-4-4.
    5. Scirtidae- marsh beetles, once Helodidae. The larvae are aquatic detritivores in dense debris, they have a tapered body and a very long, many-segmented antennae. The adults occur on emergent vegetation, they are ovate and flattened, with five tarsal segments the fourth is lobed beneath.
    6. Limnichidae (inc. Lutrochidae)- marsh-loving beetles, the larvae and adults may be aquatic or semiaquatic. Larvae are elmid-like with the ninth segment rounded posteriorly and with movable ventral operculum with internal hooks, 5 lateral 1 ventral ocelli. The adults are pubescent, ovate, 0.8 to 5mm long, with last tarsal segment long, claws long, antennae with less than 11 segments.
    7. Dryopidae- the long-toed water beetles. The larvae may be aquatic or terrestrial, ninth segment rounded posteriorly and with movable ventral operculum, no internal hooks. The adults are aquatic with the last tarsal segment long, claws long, antennae short, front coxae transverse.
    8. Elmidae- riffle beetles, the larvae and most adults are aquatic, almost always in lotic riffles, neither is dependent on the atmosphere. The larval ninth segment with movable ventral operculum with a pair of internal hooks, 5 lateral ocelli. The adults have the last tarsal segment long, claws long, antennae usually filiform and long, front coxae globose.
    9. Ptilodactylidae- toed-winged beetles, the larvae may be aquatic, they are elmid-like, but lack the operculum, numerous anal gills are present. The adults are terrestrial, elongate, soft bodied, with a heart-shaped scutellum.
    10. Heteroceridae- variegated mud-loving beetles, the larvae and adults burrow on beaches. The larvae are tapered, clothed with setae, mouthparts prognathous; adults have the tibiae dilated and very spiny, antennae with a 7 segmented serrate club.
    11. Psephenidae (inc. Eubriidae)- water pennies. The larvae are aquatic, erosional zone scrapers, the body is very flattened, the tergites are expanded laterally to cover the entire body. The adults are short-lived and terrestrial, the body is broad and depressed. Some pupate underwater.
    12. Lampyridae- firefly beetles. The larvae can be aquatic or semiaquatic snail predators, they have the tergites expanded laterally. The adults are terrestrial, they have the pronotum covering the head. Some species have luminescent lanterns.
    13. Chrysomelidae- leaf beetles, mostly terrestrial, but the larvae of some species feeding inside submerged vascular plants. The larvae are short and obese with reduced legs. The adults are have 4 visible tarsal segments, the first 3 of which are dilated with hairy pads.
    14. Curculionidae- weevils, mostly terrestrial, aquatic species associated with vascular plants, larvae with short obese body without legs; adults with the head prolonged into a snout and geniculate antennae.

Montana Species list

Reference update

Some genus level name changes

Some species level name changes

Other Sites

Updated on 23 NOV 1995 D.L. Gustafson
AIM home page
dlg@rivers.oscs.montana.edu