Whirligig beetle

Behavior and morphological adaptations

The Gyrinidae are surface swimmers for preference. They are known for the bewildering and rapid gyrations in which they swim, and for their gregarious behavior. Most species also can fly well, even taking off from water if need be. The combination constitutes a survival strategy that helps them to avoid predation and take advantage of mating opportunities. In general the adults occupy areas where water flows steadily and not too fast, such as minor rapids and narrows in leisurely streams. Such places supply a good turnover of floating detritus or struggling insects or other small animals that have fallen in and float with the current.

The positions that individuals occupy within a group are determined by a number of factors, thought to include hunger, sex, species, water temperature, age, parasite level and stress level. Research underway on their behavior is directed at investigating the significance of chemical defense in relation to their position in the group. Such studies are of interest in research into aspects of nanotechnology because the beetles' motion may be expected to provide insights into how groups of robots might coordinate movements.

In particular the beetles make behavioral trade-offs that affect their choices of positions within a group. For example, relatively hungry beetles go to the outside of a group, where there is less competition for finding food, but higher risk of encountering predators. Males are also more likely to be found on the outside of groups (although grouping is not known to be relevant to mating behavior in this family). The economies that the beetles can gain by suitably adjusting their positions within the group, are important when individuals swim against the flow of a stream. By swimming behind other beetles they can take advantage of forward-moving drafts. Such action is called drafting. The determination of forward/backward positioning within a group has been found to be affected in a complex manner by a combination of water speed, sex of the beetle, and the type of predator (bird or fish) that a beetle has most recently observed.

The beetles could use the waves generated by their moving as a sort of radar to detect the position of object on the water surface around them. This technique could be used to detect prey or to avoid colliding each other.

The adult beetles carry a bubble of air trapped beneath their elytra. This allows them to dive and swim under well-oxygenated water for indefinite periods if necessary. The mechanism is sophisticated and amounts to a physical gill. In practice though, their ecological adaptation is for the adults to scavenge and hunt on the water surface, so they seldom stay down for long. The larvae have paired plumose tracheal gills on each of the first eight abdominal segments.

Generally, gyrinids lay their eggs underwater, attached to water plants, typically in rows. Like the adults, the larvae are active predators, largely benthic inhabitants of the stream bed and aquatic plants. They have long thoracic legs with paired claws. Their mandibles are curved, pointed, and pierced with a sucking canal. In this they resemble the larvae of many other predatory water beetles, such as the Dytiscidae. Mature larvae pupate in a cocoon that also is attached to water plants.

Taxonomy

Whirligig beetles were previously grouped with other aquatic members of the Adephaga such as Dytiscidae, as members of the group "Hydradephaga". However based on molecular evidence they are currently thought to be the earliest diverging lineage of the Adephaga, and to have evolved their aquatic ecology independently from other adephagans. Cladogram after Vasilikopoulos et al. 2021

Internal taxonomy

Taxonomy after

• Spanglerogyrinae Folkerts, 1979
  • †Angarogyrus Ponomarenko, 1977 - Early Jurassic-Early Cretaceous, Asia
  • Spanglerogyrus Folkerts, 1979 - North America

• Heterogyrinae Brinck, 1955
  • †Mesogyrus Ponomarenko, 1973 - Late Jurassic-Early Cretaceous, Asia
  • Heterogyrus Legros, 1953 - Madagascar
  • †Cretotortor Ponomarenko, 1973 - Late Cretaceous-Paleocene (Asia)
  • †Baissogyrus Ponomarenko, 1973 - Zaza Formation, Russia, Early Cretaceous (Aptian)

• Gyrininae Latreille, 1810
  • Dineutini Desmarest, 1851
    • †Cretodineutus Liang et al., 2020 - Burmese amber, Late Cretaceous (Cenomanian)
    • †Cretogyrus Zhao et al., 2019 - Burmese amber, Cenomanian
    • Dineutus MacLeay, 1825
    • Enhydrus Laporte, 1835
    • Macrogyrus Régimbart, 1882 (including Andogyrus Ochs, 1924)
    • †Mesodineutes Ponomarenko, 1977 - Darmakan Formation, Russia, Danian
    • †Miodineutes Hatch, 1927 - Germany, Miocene
    • Porrorhynchus Laporte, 1835
  • Gyrinini Latreille, 1810
    • Aulonogyrus Motchulsky, 1853
    • †Gyrinoides Motchulsky, 1856
    • Gyrinus Geoffroy, 1762
    • Metagyrinus Brinck, 1955
  • Orectochilini Régimbart, 1882
    • Gyretes Brullé, 1835
    • Orectochilus Dejean, 1833
    • Orectogyrus Régimbart, 1884
    • Patrus Aubé, 1836
  • †Chimerogyrus Gustafson, Michat & Balke, 2020 - Burmese amber, Cenomanian
• Incertae sedis
  • †Anagyrinus Handlirsch, 1908 - Insektenmergel Formation, Switzerland, Early Jurassic, Hettangian
  • †Gyrinopsis Handlirsch, 1908 - Insektenmergel Formation, Switzerland, Early Jurassic, Hettangian