Major Group: Insecta
Order: Coleoptera
Family: Elmidae (formerly Helminthidae) |
Descriptive Features:
Adults
antennae 11-segmented without distinct club
frontoclypeal suture distinct
ventral portion of the notum, (hypomeron) on each side joined directly to the sternum by notosternal suture and pleuron reduced and concealed
plastron present in s.f. Elminae
plastron replaced by coarse hairs in s.f. Larinae
posterior edge of pronotum simple
abdomen with at least 3 connate ventrites
elytra exposing less than 2 complete abdominal tergites
tarsi 5-segmented
size: 0.95 - 6.0mm
Larvae
antennal length less than head width
labrum separated from head capsule by complete suture
mandibular mola absent
body usually elongate, some Kingolus are broad and flat
abdominal apex with ventrally hinged operculum concealing 3 extrusible tufts of fine, slender gills, 2 anal hooks on operculum
legs 5-segmented, including claws
size: up to 8 - 10 mm |
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Coxelmis larva |
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Notriolus adult |
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Taxonomic Checklist: Subfamily Genera
Elminae (adults aquatic)
Austrolimnius (53 species)
Coxelmis (3 species)
Graphelmis pallidipes Carter (formerly Stenelmis pallidipes)
Kingolus (11 species)
Notriolus (16 species)
Simsonia (16 species)
Larinae (adults riparian)
Hydora laticeps Cater & Zeck
Ovolara (2 species)
Stetholus elongatus Cater & Zeck
Potamophilinus sp. - this genus is thought to occur in northern Aus. but has not been confirmed. |
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Distribution: All states
Sensitivity Rating: SIGNAL grade 7
Functional Feeding Group: shredders (adults), scrapers (larvae) |
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Mt Wills Creek near Granite Flat, Vic |
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Ecology: Instream Habitat: Elmid beetles are commonly known as riffle beetles because of their tendency to live in lotic (running water) habitats with rocky bottoms, in particular riffles, where the water is clear with high oxygen content. Elminae (Austrolimnius, Coxelmis, Graphelmis, Kingolus, Notriolus and Simsonia) species are fully aquatic with the larvae and adults living together under water, whereas the adults of Larainae (Hydora, Ovolara and Stetholus) species are riparian often living at the edges of fresh waters. Larvae of all species live on the substrata of streams, clinging to submerged tree branches, under submerged rocks or to moss covered rocks.
Feeding Ecology: Riffle beetles feed on algae and fine detritus, with wood dwelling beetles feeding on waterlogged wood with its associated algae and fungi.
Habit: Elmid larvae are totally aquatic, breathing by means of tracheal gills. Elminae adults are able to stay permanently submerged by using a plastron. A plastron forms when specialised hairs trap a thin layer of oxygen around the abdomen. As the beetle breaths, the layer of air is used and the concentration of oxygen within the air-bubble decreases compared to the concentration of oxygen in the water causing diffusion of new oxygen across the plastron membrane. Elmidae species therefore are restricted to well-oxygenated waters. Larainae adults cannot remain permanently submerged. Larvae and adults of all species crawl on submerged substratum and are unable to actively swim.
Life History: Riffle beetle larvae go through 5 to 7 instars. Final instar larvae develop a series of spiracles on the side of the body, which allow them to emerge from the water. These mature larvae pupate in the damp areas of the stream bank where they are capable of surviving long periods in damp soil before pupating. For most Australian Elmidae species, the newly emerged adults return to the water without ever taking flight, however it is known that Ovolara and Stetholus species are able to fly. |
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Information Sources: Glaister 1999, Calder 1999a, Lawrence & Britton 1991, Williams 1980, Gooderham & Tsyrlin 2002
Key to Genera: Glaister 1999 (larvae), Lawrence 1992 (adults)
Key to Species: Glaister 1999 (larvae, Coxelmis, Kingolus, Notriolus, Simsonia)
Hinton 1965 (Austrolimnius adults)
Carter & Zeck 1929 (Coxelmis, Kingolus, Notriolus, Simsonia adults, incomplete) |
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