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 Major Groups | Acarina / Acari (mites)

Acarina / Acari (mites)

Mites are a major component in benthic and hyporheic communities of freshwater systems, but can be left behind or left unidentified due to their small size. Mites are distinguished from spiders by the body form. Water mites have the cephalothorax and abdomen completely fused whereas the spider body is divided into two parts, head/thorax (cephalothorax) and abdomen. The red, green, blue or yellow body colours of living mites are distinctive although not necessarily species specific. They can often be seen as little coloured dots zipping around in an invertebrate sample. Fish find the red coloured species distasteful but may eat the other species on occasion.
True aquatic mites belong to the Minor Group Hydracarina and Halacaroidea. However, some species from other Minor Groups are frequently collected in routine monitoring.

Descriptive Features:

  • antennae absent
  • 2 pairs of feeding appendages
  • body with no sign of external division or segmentation, often globular but may also be flattened or depressed dorsally, body surface may be smooth, rough, leathery, soft, or sclerotised
  • 4 pairs of legs, frequently fringed with swimming hairs
  • Total length: up to 5 mm
  • Taxonomic Checklist:
    Hydracarina / Hydrachnidiae 

    Distribution: Australia wide

    Sensitivity Rating: SIGNAL grade 6. Mites are particularly sensitive to heavy metals. Some species can tolerate moderate salinity but do not occur in highly saline waters.

    Functional Feeding Group: predators, scrapers, parasites 

    Ecology: Aquatic mites can be found in virtually every freshwater habitat in Australia with those from the Hydracarina group most common. Mites are most abundant in sheltered, shallow vegetated areas of standing and sluggish flowing waters, even in pools of temporary streams. They live both within the substratum and amongst the submerged vegetation. Those species that are semiaquatic are found in damp leaf litter, reeds, under stones and pieces of wood at the margins of water bodies. Species from running waters have depressed bodies, strong claws and lack the fringing setae on their legs. These mites tend to crawl and clamber rather than swim like those species in standing waters.
    The life cycle of mites consists of four stages. The eggs are laid singly or in groups on aquatic plants. The larval stage, which differs markedly from later stages by the possession of only six legs and a highly modified set of mouthparts, is called the ectoparasitic phase. The larvae have been found in freshwater mussels, dragonfly imago and in the eyes of Notonectidae (bugs). By parasitising aerial insects the mites have an effective means of dispersal. The mite larvae attach by their enlarged mouthparts until they become fully engorged then drop off and undergo metamorphosis. The short lived nymph is similar to the adult but lacks the genital field. The nymph attaches to a submerged surface and undergoes a moult into the fully developed adult. Both nymphs and adults are predators feeding primarily on small aquatic insects and crustaceans. Water mites feed by sucking the body fluids from their prey.



    Hydracarina / Hydrachnidiae








    Information Sources: Krantz & Walter 2009, Harvey & Growns 1998, Harvey 1998, Williams 1980, Hawking & Smith 1997, Halliday 2000, Davis & Christidis 1997, ABRS 2009

    Note: New keys to groups and families exist in Krantz & Walter 2009, however that book includes world taxa and no new Australian aquatic families have been recorded since 1998 so the keys in Krantz & Walter 2009 are not included in the Bug Guide.

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