Coleoptera
Coleoptera are one of the largest group of freshwater macroinvertebrates. Their exoskeleton are strongly sclerotised and their elytra are modified into a hard cover for protection. They are found in many aquatic habitats including streams and wetlands in Hong Kong. Most of them are predaceous and are important components of aquatic food chain.
Only few studied water beetles in Hong Kong and therefore identification down to species levels are difficult. Some species are identified down to subfamily or genus level, and apparent species are placed into different morphospecies. There are nine families of adult water beetles and ten families of larvae water beetles, but only Dytiscidae, most Elmidae, Gyrinidae and Hydrophilidae are fully aquatic in both adults and larvae stage.
Keys to the families of adult freshwater Coleoptera in Hong Kong:
| 1a | Compound eyes divided into separate segments, either completely separated or with a dividing ridge; antenna short and clubbed; second antennal segment elongate and scoop-shaped | Gyrinidae |
| b | Compound eyes undivided; antennae variable but without scoop-shaped second antennal segment | 2 |
| 2a | Hind coxal plates completely covering 2 or 3 basal abdominal segments and concealing all but apices of hind femora; beetles more than 2mm long | Halipidae |
| b | Hind coxal plates not broadened or covering abdominal segments | 3 |
| 3a | Hind coxae with medial portion extending posteriorly to divide 1st abdominal sternite into lateral sclerites; prothorax with distinct notopleural sutures; hind tarsi and usually tibiae flattened, stream lines and bearing long, stiff swimming bristles | 4 |
| b | Hind coxae not extending posteriorly to divide 1st abdominal sternite; notopleural sutures almost always absent | 6 |
| 4a | Fore and middle tarsi with 5 segments, segment 4 similar to size to segment 3; scutellum concealed or exposed | 5 |
| b | Fore and middle tarsi four-segmented or with segment 4 very small and concealed between lobes of segment 3; scutellum concealed | Dytiscidae(in part) |
| 5a | Hind tarsi with 2 similar claws; scutellum concealed | Noteridae |
| b | Hind tarsi with single claw; if 2 claws, scutellum exposed | Dytiscidae (in part) |
| 6a | Antennae terminating in abrupt, globular or elongate, 3-5 segmented club | 7 |
| b | Antennae slender, elongate or very short, thick with basal segment enlarged | 8 |
| 7a | Eyes protruding; pronotum narrower than base of adjoining elytra; scutellum small; antennae with 3 or fewer segments before cupule (base of terminal club) | Hydrochidae |
| b | Eyes usually not protruding; pronotum not distinctly narrower than elytra (if narrower than scutellum is large); antennae often have 5 segments before cupule | Hydrophilidae |
| 8a | Prosternum expanded anteriorly as prominent lobe beneath head, head usually contracted into thorax concealing antennae and eyes | Elmidae (in part) |
| b | Prosternum not markedly expanded anteriorly beneath head, antennae clearly visible | 9 |
| 9a | Tarsi with 4th sgment deeply bilobed | Scirtidae |
| b | Tarsi usually filiform, 4th sgment not bilobed | Elmidae |
The above key is adopted and modified from Merritt and Cummins (2008).
The following list of Coleoptera present in Hong Kong combined the survey efforts of Paul Aston (2013-2014) and Ken So (2014-present). Photos of some specimens are not yet taken and hence not available here.
Coleoptera (Beetles) - Adults |
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Dytiscidae
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Elmidae Halipidae Gyrinidae Hydrochidae Hydrophilidae |
Hydrophilidae (continued) |
Limnichidae Noteridae Scirtidae |
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Coleoptera (Beetles) - Larvae |
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Dytiscidae Elmidae Gyrinidae
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Hydrophilidae
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Lampyridae Limnichidae Noteridae Psephenidae Ptilodactylidae |
Scirtidae
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Reference:
Merritt, R. W., & Cummins, K. W. (Eds.). (1996). An introduction to the aquatic insects of North America. Kendall Hunt.