Major Group: Insecta
Order: Coleoptera
Family: Gyrinidae |
Descriptive Features:
Adults
head not exserted
eyes divided into dorsal and ventral portions
antennae very short and thick, with less than 11 segments, the first of which is very large, length always greater than 1 mm, entirely or almost entirely glabrous
dorsal surfaces rarely with erect, fixed sensory setae
elytra truncate exposing most of one abdominal tergite
abdomen with ventrite 1 divided into 2 or 3 parts by hind coxae
prothorax with pair of notopleural sutures (distinct from sharp lateral margins) separating notum from externally visible pleuron on each side
metasternum without transverse suture, if suture present, then elytra without regular puncture rows
mesocoxal cavities open laterally (partly closed by mesepimeron)
metacoxal plates absent or consisting of narrow mesal portion only, not concealing basal ventrites or femora
metacoxae lateral portions longer than metasternum
metacoxae extending laterally to meet elytra, so that junction of metepimera and first ventrite is not visible
tarsi always 5-segmented
fore tibia without antenna cleaner
forelegs long, raptorial
mid- and hindlegs short, paddle-like
size: 3.5 - 15.0mm
Larvae
maxillary palp, 4-segmented
mandibles narrow and falcate, with internal perforation
labial palps 3-segmented
labrum completely fused to head capsule
antennae longer than head width
body long, thin
abdominal segments 1-8 with lateral gills
abdominal tergum 9 without paired urogomphi, sometimes with 2 pairs of gills
abdominal segment 10 not or only slightly longer than 9, with 2 pairs of hooks at apex
legs 6-segmented, including pretarsus (claws)
size: up to 20mm |
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Gyrinidae larva |
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Aulonogyrus strigosus adult |
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Taxonomic Checklist: Genera
Aulonogyrus strigosus Fabricius
Dineutus 2 species
Gyrinus convexiusculus MacLeay
Macrogyrus 15 species |
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Distribution: Australia wide
Sensitivity Rating: SIGNAL grade 4
Functional Feeding Group: predators |
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Murray River at Cottadidda State Forest, NSW |
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Ecology: Instream habitat: Gyrinid beetles occur at the edges of small lakes, in ponds, small dams, and within slow flowing, sheltered sections of creeks and rivers. Adults of Gyrinidae species are the only beetles to inhabit the water surface in both lotic and lentic habitats.
Feeding ecology:Adults are predators on insects which have fallen into or have become trapped within the water surface film. They locate prey using a specialised organ, within the antennal pedicel, which is sensitive to surface waves. Larvae are bottom dwelling predators and feed on a variety of soft-bodied animals e.g. worms, chironomid larvae or odonate nymphs.
Habit: Gyrinid adults are commonly known as ‘whirligig beetles’ reflecting their habit of rapidly skimming across the water surface in a circular pattern. They are usually active during daylight and found in small to large groups until they are disturbed, when they will actively seek cover in vegetation. The circular swimming pattern comes from having flattened, paddle-like mid- and hind-legs that are shorter than the forelegs. The beetles are able to skim the water surface with the aid of surfactants secreted by pygidial glands. Eyes of adults are separated into upper and lower pairs allowing the beetles to see above and below the water simultaneously. Larvae remain submerged through all instars and obtain oxygen from the water through abdominal gills.
Life history: In North America gyrinid beetles copulate on the water surface and then the female lays her eggs on stems of emergent vegetation a few centimetres below the waters surface. After hatching larvae pass through two to three instars. The final instar larvae climb onto emergent vegetation or crawl onto shore where they form a mud or sand cocoon for pupation. |
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Information Sources: Watts 2002, Lawrence & Britton 1991, Williams 1980, Gooderham & Tsyrlin 2000, Lawrence et al. 2002a
Key to Genera: Watts & Hamon 2010 (adults, larvae – excluding Gyrinus), Watts 2002 (adults, larvae - Aulonogyrus & Macrogyrus not separated)
Key to Species: Watts & Hamon 2010 (adults, larvae) |
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