(= HELMINTHIDAE, ELMINTHIDAE)

Riffle beetles

Code QC340000

Larvae elongate to ovate, length 2mm to over 20mm when mature. When broadly ovate, elmid larvae may be distinguished from psephenids by the head, which is visible in dorsal view. Elmid larvae possess short, three segmented antennae, which easily distinguishes them from scirtids, and stemmata (5 pairs) closely clustered to form a single eye. The legs are well developed with 5 segments, the apical segment forming a single tarsungulus (claw). The ninth abdominal segment forms an operculate gill chamber into which three pairs of filamentous anal gills are retracted. The operculum bears two hooks. This combination of gill characters readily distinguishes elmids from all other larvae. Urogomphi absent.

Elmid larvae (Polyphaga, placed in Byrrhoidea by Australian authors, Dryopoidea by American authors) live in clear, generally somewhat shallow, running water, and occur throughout Australia. Currently, around 150 species are recognised from over 8 genera. Many are highly substrate specific, for example algal grazers tend to be associated almost exclusively with cobbles, and Australia possesses a diverse and abundant xylophagous (wood-feeding) elmid fauna. In native-forested mountain streams, xylophagous elmids, including Notriolus and some Simsonia species, are important processors of submersed wood. Their gouging mode of feeding increases the surface area available on woody substrates for utilisation by decaying organisms (fungi and bacteria) and other macroinvertebrates, and they probably also have a crucial role in nutrient cycling, reducing the biomass locked away within wood and associated fungi to a particulate form useable by gathering animals. Adult elmids are found in similar habitats to corresponding larvae, but appear to be less specialised, mostly being generalist particulate detritivores.

References:

Brown, H.P. (1991) Elmidae (Dryopoidea) pp. 404-407. In: Stehr, F.W. (ed.) Immature Insects. Volume 2. Kendall/Hunt Publishing Company, Dubuque, Iowa.

Lawrence, J.F. and Britton, E.B. (1991) Coleoptera. pp. 543-683. In: CSIRO, Insects of Australia. Volume 2. Melbourne University Press, Carlton, Victoria.

M c Kie, B.G. (1996) The Community Ecology of Wood-Associated Macroinvertebrates in Streams of the Brindabella Ranges, Australia. Honours Thesis, Australian National University.