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Digitizing and providing web access to this text was funded in part by the Alberta Conservation Association and the University of Alberta, Department of Biological Sciences

Coleoptera(Beetles)


Introduction

Coleoptera, the beetles, is the largest order of insects in terms of number of species. There are about 250,000 described species of beetles, representing about 20% of all extant species of known multicellular animals. Most beetles are entirely terrestrial. Of the 18 families with freshwater representatives in North America, 12 or 13 are found in Alberta. Dytiscidae is the largest family of aquatic beetles in Alberta; there are about 150 species of dytiscids in the province (Larson 1975).

General Features

Both larvae and adults of the aquatic families are usually aquatic. Exceptions are the Scirtidae (Scirtes and Cyphon), where the larvae are aquatic and the adults are terrestrial, Helichus (Dryopidae), which has aquatic adults and terrestrial larvae, and Limnichus (Limnichidae), in which adults are probably semi-aquatic and the habitat of the larvae is unknown. Beetles are found in all types of aquatic habitats, being more numerous and diverse in standing water than in running water. Both adults and larvae are found mainly on the substratum; however, some, e.g. Dytiscidae and Gyrinidae, are active swimmers. Although adults of all families except Scirtidae are found in water, they are generally good fliers, and via flying can disperse to new aquatic habitats.

Feeding, Life Cycle

There is much variation in feeding habits, both in the adult and larval stages. Some are herbivorous, some omnivorous, and some are active and voracious predators. Generally, aquatic beetles oviposit beneath the surface of the water. Although little is known about specific life cycles of most aquatic beetles in Alberta, temperate aquatic beetles are mainly univoltine, but some can have cycles of two or more years. There is no fixed number of larval instars; for example dytiscids, hydrophilids, gyrinids and haliplids have three larval instars; whereas elmids might have five or more. Generally, the larva crawls out of the water to pupate in what is called a mud cell, which is usually constructed near the water line.

Collecting, Identifying, Preserving

Pond-net sampling is suitable for collecting most adults and larvae; but mature larvae and adults can be very small, about 2 mm in length, and a fine-meshed pond-net is needed to collect these beetles. And of course samples have to be thoroughly searched for small specimens. Many adult aquatic beetles will be inactive and therefore inconspicuous when the sample is brought out of the water. If the sample is placed in a white enamel pan and allowed to dry for awhile, the beetles, when they start to dry out, will become active and are easily spotted in the sample. Most adults and larvae tend to be in very shallow water near the water's edge, often amongst dense emergent vegetation or debris. Successful beetle collecting depends on having a sturdy net that can sweep through the tangled vegetation, such as sedges, and can scoop up the debris of the substrata.

Many of the features called for in the adult keys are best seen by examining the specimen when it is dry (Fig 41.1). This is especially true of hairs and suture-like features, which are difficult to see on dark specimens immersed in fluid. Another method is to soak beetles in about a 3% solution of sodium hydroxide, before examining the specimens. About 80% ethanol is usually a good preservative for both larvae and adults, although some workers prefer to pin the adults. However, many workers prefer initially to kill and fix the larva with boiling water or with Kahle's solution (see Trichoptera chapter), especially to maintain the color and distend the specimen. Figure 41.1 shows anatomical features needed to identify most adult beetles.

See Pennak (1978), McCafferty (1981) and White et al. (1984) for keys to genera of larval and adult aquatic beetles of North America. White's (1983) A Field Guide to the Beetles of North America covers all families and is valuable in recognizing terrestrial beetles that are accidental in aquatic samples. The families are treated in the text in alphabetical order.

Aquatic Coleoptera Families of Alberta

  • Family Amphizoidae—trout stream beetles
  • Family Chrysomelidae—leaf beetles
  • Family Curculionidae—weevils
  • Family Dryopidae—long-toed water beetles
  • Family Dytiscidae—predacious water beetles
  • Family Elmidae—riffle beetles
  • Family Gyrinidae—whirligig beetles
  • Family Haliplidae—crawling water beetles
  • Family Hydraenidae—minute moss beetles
  • Family Hydrophilidae—water scavenger beetles
  • Family Lampyridae—fireflies and relatives
  • Family Limnichidae—marsh-loving beetles
  • Family Scirtidae—marsh beetles

Amphizoidae (trout stream beetles)

These beetles, never very abundant, appear to be most common in the Rocky Mountains foothills and mountain streams of southern Alberta (see order key and Plates 41.3 and 41.12). Both adults and larvae slowly crawl along the substratum, and both larvae and adults are usually found along the edges of streams, quite often being associated with woody material-"debris dams" out of the current are good places to collect them.

Amphizoid beetles are predacious. Their major prey is stonefly (Plecoptera) larvae (White et al. 1984). Little is known about pupation. Edwards (1954) found surprisingly large eggs (with a diameter of over 1 mm), which were fastened in cracks underneath driftwood. The single genus is Amphizoa (Plates 41.2 and 41.8). Adults are large, up to about 15 mm in length, and larvae are distinct because of the laterally expanded plates of the body.

Chrysomelidae (leaf beetles)

This is a large family of mainly terrestrial beetles, called leaf beetles because they feed on leaves. At least four aquatic genera are found in Alberta (see CHRYSOMELIDAE ADULTS and LARVAE pictorial keys): Donacia (Plates 41.3 and 41.5), Plateumaris (formerly a subgenus of Donacia), Macro plea (=Neohaemonia) (Plate 41.5) and Pyrrhalta (=Galerucella) (Plates 41.3 and 41.5). Both larvae and adults feed on aquatic plants, especially water lilies. Larval and adult Pyrrhalta feed only on the top surfaces of floating aquatic plants; whereas Donacia can feed on the submerged part of aquatic plants as well (White et al. 1984).

Hoffman (1940a, 1940b) studied Donacia species in northern Michigan. Following is a synopsis of some of his findings. Species had a preference for a single or at most a few aquatic plants; pupation (in an air-filled silk cocoon) and subsequently mating usually took place on the same plant that was the habitat of the larva. Females deposited egg masses on plants at the water surface or above water; when the larvae hatched, they had to find the correct plant and usually migrated to the bottom of the plant before becoming established on the plant, which might be anywhere from the roots to the leaves; in Michigan, Donacia had life cycles of two or more years.

Curculionidae (weevils)

Curculionidae is another large family of mainly terrestrial beetles. Adults are easily distinguished from other beetles by their snout (see order key and Plate 41.6), which in aquatic weevils is not as long as in some terrestrial adults. Larvae are also readily separated from other beetle larvae, because curculionid larvae do not have legs. But do not confuse them with certain dipteran larvae. As true for aquatic Chrysomelidae, both larvae and adult curculionids are associated with aquatic plants. The legless larvae mine into the plants and feed; whereas the adults feed on plant material from the outside. Therefore larvae will rarely be collected unless one collects and dissects the host plants. For example, Tanysphyrus is a miner in duckweed (Lemna). Pupation usually takes place in or on the host plant. The eggs of at least some species are inserted into the host plant.

There are relatively large numbers of genera in which at least one species is suspected of being aquatic or semi-aquatic. At least eight genera with aquatic representatives are found in Alberta: Bagous (Plate 41.6), Euhyrichopsis (Plate 41.6), Lissorhoptrus, Litodactylus (Plate 41.6), Lixellus (Plate 41.6), Notiodes (=Endalus), Phytobius, and Tanysphyrus. Notiodes is common in Alberta.

Dryopidae (long-toed water beetles)

Helichus is apparently the only aquatic genus of Dryopidae occurring in Alberta (see order key and Plate 41.12). All larvae of this genus are apparently terrestrial, but adults are aquatic, living mainly in running water. Little is known about the biology of these beetles. Adults are reported to be herbivorous (Leech and Chandler 1956). Adult Helichus striatus LeConte, perhaps the only species in the province, is about 6 mm in length.

Dytiscidae (predacious water beetles)

This is the major family of entirely aquatic beetles in Alberta (see DYTISCIDAE ADULTS and LARVAE pictorial keys). World-wide, there are about 3,000 species. In Alberta, about 150 species have been described (Plates 41.1 and 41.6). Specimens of Hydroporus are perhaps the most common adult aquatic beetles in Alberta. Dytiscidae contains some of the smallest adult aquatic beetles (1.5 or 2 mm in length) and also the largest adults (Dytiscus, to 40 mm). Dytiscids are found in a wide variety of both standing and running water habitat. Many species can be collected from shallow regions of ponds, especially in vegetation. A sturdy dip net very actively worked (some of the large adults and perhaps larvae can avoid slow-moving objects) through weedy areas usually yields numerous dytiscids. Larvae are usually found on the substratum, but the adults are good swimmers-and also very good fliers.

Both larvae (Plate 41.1) and adults (Plates Plate 41.9 - Plate 41.12 ) are predacious, some large larvae and adults even subduing and eating small fish. Adults trap air beneath the elytra and can remain submerged for long periods before coming to the surface to replenish the air through spiracles at the tip of the abdomen. Most larvae also come to the surface to replenish their oxygen supply. Pupation takes place out of water but usually near the water. The eggs are deposited in a variety of locations: above the water line, inserted into aquatic plants or on the plants; the different ovipositing sites appear to be correlated with the type of ovipositor of the female (Brigham 1982). Most Alberta species have only one generation a year and overwinter as adults (Larson 1975).

The DYTISCIDAE ADULTS pictorial keys follow mainly the diagnostic features of Larson (1975). Species of the genera listed below have been reported from Alberta. Almost all records are from Larson (1975) (see Larson for species of Dytiscidae in Alberta).

Subfamily Dytiscinae: Acilius (Plate 41.9), Dytiscus (Plates 41.11 and 41.12), Graphoderus (Plates 41.1 and 41.11), Hydaticus (Plate 41.10)

Subfamily Colymbetinae: Agabus (Plate 41.11), Carrhydrus, Colymbetes (Plate 41.9), Coptotomus (Plate 41.11), Nybius (Plate 41.10), Neoscutopterus (Plate 41.9), Rhantus (Plate 41.9)

Subfamily Hydroporinae: Desmopachria (Plate 41.11), Hydroporus (Plate 41.10), Hygrotus (Plate 41.10), Laccornis (Plate 41.10), Liodessus (Plate 41.10), Potamonectes (Plate 41.9), Oreodytes (Plate 41.9)

Subfamily Laccophilinae: Laccophilus

Elmidae (riffle beetles)

Elmidae is an entirely aquatic family (see ELMIDAE ADULTS and LARVAE pictorial keys). Both adults and larvae are found crawling on the substratum (Plates 41.2 and 41.5). Although called riffle beetles, they can be found in fairly slow-moving areas of streams as well. Elmids are found throughout Alberta. Most adults are rarely over 4 mm in length. The hard-bodied larvae are distinctive and can only be confused with larvae of dryopids, but dryopid larvae are terrestrial.

There are few complete life cycle studies of elmids. White (1978) described the life cycle of a Stenelmis sexlineata Sanderson. Although this genus has not been reported from Alberta, its life cycle is probably typical of many elmids. Stenelmis larvae apparently did not leave the riffle to pupate, but relied on water level fluctuations to leave the mature larva out of water where pupation took place. After the adults emerged from the pupae, they had a short flight period, but after entering the water did not fly again. Eggs were laid on the undersides of submerged rocks.

The following genera have been reported from Alberta: Cleptelmis, Dubiraphia (Plate 41.2), Heterlimnius, Narpus (Plates 41.2 and 41.5), Optioservus (Plate 41.2), and Zaitzevia.

Gyrinidae (whirligig beetles)

Gyrinus is the common Alberta genus of this entirely aquatic family, but Dineutus, which had been known from north-central Saskatchewan, has now been collected in Alberta (Carr 1990) (see order key). Adult gyrinids are distinctive because of their divided eyes. Both larvae and adults are found in all types of aquatic habitats (Plates 41.1 and 41.6).

The shiny-looking adults are often conspicuous, with their gyrating (hence the name) movements on the water's surface. They are rarely observed diving beneath the water. Adults are sometimes found in aggregations, which might contain more than one species (Hilsenhoff et al. 1972). Pupation takes place on shore. Eggs are laid on aquatic plants. Larvae are predacious, while adults, which are strong fliers, are more scavenger, feeding on trapped insects on the water's surface. At least 11 species of Gyrinus have been recorded from Alberta.

Haliplidae (crawling water beetles)

Haliplids are common throughout much of Alberta. Adults of this family are distinctive because of their greatly expanded coxal plates (see HALIPLIDAE ADULTS and LARVAE pictorial keys). Three of the four genera of North America haliplids are found in Alberta: Brychius (Plate 41.2), Haliplus (Plates 41.2 and 41.4) and Peltodytes (Plate 41.4). (The rare Apteraliplus apparently does not occur in Alberta). Both larvae and adults can be collected from aquatic vegetation of standing waters, such as ponds and marshes, but some occur in shallow water areas of streams.

Both adults and larvae are mainly herbivorous. For species of Wisconsin, Hilsenhoff and Brigham (1978) found that most probably had one-year life cycles, with the adults overwintering. Pupation took place in moist soil out of water, but near the water line, and the females deposited eggs in or on algae.

Hydraenidae (minute moss beetles)

Both larvae and adults of this family superficially resemble larvae and adults of some hydrophilids (see HYDRAENIDAE ADULTS and LARVAE pictorial keys). But both larva and adult hydraenids are small, rarely over 2 mm in length (Plate 41.4 ).

They are found in a variety of aquatic habitat (the adults sometimes on shore), but rarely in moss. Hydraenids do not appear to be very abundant in Alberta; but perhaps, in part, this is due to being overlooked because of their small size.

Adult and larvae of Ochthebius and a smaller percentage of Hydraena are found in standing waters; whereas Limnebius adults and larvae are often found at the margins of clear, sandy rivers (Perkins 1980). By stirring the substratum, these little beetles will float to the surface. According to Perkins (1980): "Since they cannot swim, these tiny beetles become trapped in the surface film, appearing as silvery specks due to their ventral air bubble. While in this inverted position, a beetle is able to walk about on the underside of the surface film, and when near an emergent object the floating beetle is immediately pulled to the object by surface tension, and rapidly crawls beneath the surface." Larvae and adults appear to be mainly herbivorous; eggs are deposited on woody substrata or small rocks beneath the water's surface (Perkins 1975).

Species of Hydraena, Ochthebius (including Gymnochthebius) and Limnebius occur in Alberta.

Hydrophilidae (water scavenger beetles)

This family contains both aquatic and terrestrial representatives (see HYDROPHIUDAE ADULTS and LARVAE pictorial keys). It is of course the aquatic group of the family that is called water scavenger beetles. In Alberta, at least 15 genera encompassing over 40 species are known to occur (Plates 41.1, 41.7, and 41.8). Adults and larvae are found in both standing and running water, perhaps being most abundant in ponds. Although the family is called water scavenger beetles, larvae are apparently mainly predacious. It is the adults that are mainly scavenger, being both omnivorous and herbivorous. Both larvae and adults come to the surface to replenish their oxygen supply.

Pupation takes place out of water, in a mud cell not far from the water. Females deposit eggs enclosed within a silken egg case, which is attached to aquatic plants. Helophorus is the largest genus of hydrophilids in Alberta, and specimens of Helophorus are one of the first beetles to move into snowmelt pools in the spring (Carr 1990). Species of the following genera probably occur in Alberta: Ametor (Plate 41.7), Anacaena, Berosus (Plates 41.1and 41.8), Cercyon (Plate 41.7), Crenitis (Plate 41.7), Cymbiodyta (Plate 41.8 ), Enochrus (Plate 41.8 ), Helophorus (Plates 41.1 and 41.7), Hydrobius (Plate 41.7), Hydrochara (Plate 41.8), Hydrochus, Hydrophilus (Plate 41.1), Laccobius (Plate 41.8), Paracymus (Plate 41.8), and Tropisternus (Plate 41.7 ).

In the key to larvae of Hydrophilidae, Anacaena and Paracymus would key together. The mandible of Paracymus has three prominent teeth (see pictorial key), whereas the mandible of Anacaena has three prominent teeth and a very small fourth tooth. Adult Anacaena will key with Crenitis. Adult of these two genera are small, about 2 mm in length; Anacaena has a protuberance on the mesosternum before the middle coxae, whereas Crenitis lacks this protuberance.

Lampyridae (fireflies and relatives)

Lampyridae is usually not treated in manuals of aquatic insects, although White et al. (1984) include the larvae in their key to aquatic beetle families. A few larval lampyrids (genera unknown) have infrequently but consistently been collected from littoral regions of lakes in Alberta (see order key). These larvae are apparently either aquatic or semi-aquatic (Plate 41.3).

Limnichidae (marsh-loving beetles)

Both larvae and adults of most limnichids are terrestrial, but some adults are found near water. In Alberta, Limnichus alutaceus (Casey) has been recorded from Alberta (Carr 1990) (Plate 41.5). These adults would probably key to the DRYOPODAE-ELMIDAE section, but Limnichus is hairy and less than 2 mm in length. The larvae are presumed to be terrestrial. Liminchidae is not included in the pictorial keys.

Scirtidae(=Helodidae) (marsh beetles)

Adults of Scirtidae are terrestrial and the larvae are aquatic (see order key and Plates 41.2 and 41.5). Larvae are quite small, usually less than 5 mm in length and are distinct from larvae of other families because of their long antennae. Little is known about aquatic scirtids; the larvae are found near the water's surface in standing waters. Cyphon has been recorded several times from Alberta and recently Scirtes sp. has also been collected in Alberta (Carr 1990). A Cyphon larva has a fringe of short, regularly spaced setae at the lateral margins of the middle abdominal segments; whereas a Scirtes larva has only scattered lateral setae on the abdomen.

Some Taxa Not Reported From Alberta

The other common families of North American beetles are probably not found in Alberta; these are Noteridae (the burrowing water beetles) and Psephenidae (water pennies). Both adult and larval Noteridae are aquatic, being found mainly in ponds. The noterid Suphisellus is widespread (White et al. 1984) and would probably be the one to be found in Alberta, but this is unlikely. Only larval Psephenidae are aquatic. They are distinct, having the body very much flattened due to the body segments being expanded laterally; this gives the larva an almost ovoid shape. Some larvae are up to 6 mm in length. It is unlikely that these very distinctive beetle larvae are to be found in Alberta.

Survey of References

The following references contain information on the aquatic beetles of Alberta: Aiken (1985, 1 986a, 1 986b), Aiken and Leggett (1984), Aiken and Roughley (1985), Aiken and Wilkinson (1985), Larson (1974, 1975, 1985, 1 987a, 1 987b, 1989), Larson and Pritchard (1974), Newhouse and Aiken (1986), Perkins (1980), Reist (1980), Wallis (1929). See also the bottom fauna references listed at the end of Chapter 3 (Porifera).

For anatomical features important in identifying adult aquatic beetles, see Figure 41.1.

Pictorial Keys

Figures

Plates

  • Plate 41.1
    Coleoptera Larvae.
    Upper, left to right: Graphoderus sp. (Dytiscidae) [12 mm], unidentified Dytiscidae larva [25 mm].
    Middle, left to right: Hydrophilus sp. (Hydrophilidae) [15 mm], Helophorus sp. (Hydrophilidae) [6 mm].
    Lower, left to right: Berosus sp. (Hydrophilidae) [8 mm], Gyrinus sp. (Gyrinidae) [15 mm].
  • Plate 41.2
    Coleoptera Larvae.
    Upper, left to right: Scirtidae larva [5 mm], Narpus sp. (Elmidae) [5 mm], Dubiraphia sp. (Elmidae) sp. [8 mm].
    Lower, left to right: Optioservus sp. (Elmidae) sp. [4 mm], Brychius sp. (Haliplidae) sp. [5 mm], Haliplus sp. (Haliplidae) sp. [6mm].
  • Plate 41.3
    Coleoptera Larvae.
    Upper, left to right: Pyrrhalta sp. (Chrysomelidae) [10 mm], Donacia (Chrysomelidae) larva [10 mm] and pupa [6 mm].
    Lower, left to right: Amphizoa sp. (Amphizoidae) [10 mm], Lampyridae larva [15 mm]
  • Plate 41.4
    Adult Coleoptera.
    Upper, left to right: Peltodytes sp. (Haliplidae)-dorsal [5 mm], Peltodytes sp. (Haliplidae) ventral [5 mm]. Halipus sp. (Haliplidae) [4 mm].
    Lower, left to right: Halipus sp. side view [4 mm],Hydraena sp. (Hydraenidae) [2 mm], Ochthebius sp. (Hydraenidae) [2 mm].
  • Plate 41.5
    Adult Coleoptera.
    Upper left to right: Pyrrhalta sp. (Chrysomelidae) [8 mm], Macroplea(=Neohaemonia) sp. [3 mm], Donacia hirticollis (Chrysomelidae) [11 mm].
    Lower, left to right: Narpus sp. (Elmidae) [5 mm], Limnichus alutaceus (Limnichidae) [2 mm], Scirtes sp. (Scirtidae) [3 mm].
  • Plate 41.6
    Adult Coleoptera.
    Upper, left to right: Litodactylus sp. (Curculionidae) [5 mm], Euhyrichopsis albertanus (Curculionidae) [6 mm].
    Middle: Lixellus sp. (Curculionidae) [7 mm].
    Lower: Gyrinus sp. (Gyrinidae) [8 mm].
    Lower right: Bagous transversis (Curculionidae) [4 mm].
  • Plate 41.7
    Adult Coleoptera (all Hydrophilidae).
    Upper,left to right: Helophorus sp. [3 mm], Hydrobius sp. [8 mm], Tropisternus sp. [12 mm].
    Lower, left to right: Ametor scabrosus [7 mm], Cercyon marinus [4 mm], Crenitis morata or digesta [4 mm].
  • Plate 41.8
    Adult Coleoptera (all Hydrophilidae). Upper, left to right: Cymbiodyta acuminata [5 mm], Enochrus collinus [6 mm], Hydrochara obtusata [22 mm].
    Lower, left to right: Laccobius sp. [4 mm], Paracymus subcupreus [3 mm], Berosus fraternus [3 mm].
  • Plate 41.9
    Adult Coleoptera (Dystiscidae).
    Upper, left to right: Acilius semisulcatus [12 mm], Neoscutopterus hornii [15 mm], Rhantus binotatus [10 mm]. Lower, left to right: Colymbetes sculptilis [18 mm], Oreodytes laevis [4 mm], Potamonectes elegans [5 mm].
  • Plate 41.12
    Adult Coleoptera. Upper, left to right: Amphizoa sp. (Amphizoidae) [15 mm], Helichus sp. (Dryopidae) [7 mm].
    Lower: Dytiscus alaskanus (Dytiscidae) [26 mm].
  • Plate 41.10
    Adult Coleoptera (all Dytiscidae). Upper, left to right: Laccornis conoideus [5mm], Liodessus affinis [2mm], Ilybius pleuriticus [12mm].
    Lower, left to right: Hygrotus sayi [3mm], Hydroporus superioris [5mm], Hydaticus modestus [12mm].
  • Plate 41.11
    Adult Coleoptera (all Dytiscidae). Upper, left to right: Graphoderus occidentalis [12 mm], Agabus anthracinus [7 mm], Coptotomus longulus [8 mm].
    Lower, left to right: Dytuscus alaskanus [26 mm], Desmopachria convexa [2 mm].