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Coleoptera (コウチュウ目)
Coleoptera is the largest order which consists of about 40 percent of all the species of the class Insecta. Its hardy elytra cover the abdomen. Elytra are often brightly colored as is the case with ladybird beetles shown in Figure 1. In Japan, elytra are regarded as armor and Coleoptera species are called as armor-bugs or kou-chu.
Figure 1. Elytra (f. Coccinellidae) Length: 6mm
The coxae, or the first segment of their metathoracic legs are highly developed, and they cover the large portion of its abdomen. Most Coleoptera we see belongs to the suborder Adephaga (オサムシ亜目) and Polyphaga (カブトムシ亜目).
Adephaga
The major characteristics of Adephaga species are well developed hind coxa that separates the first abdominal sterna. Shown in the figure 2 and 3 are of Adephaga species. Haliplidae (コガシラミズムシ科 Figure 2.) and Dytiscidae (ゲンゴロウ科Figure 3.) are aquatic beetles.
Figure 2. Crawling Water Beetle (Peltodytes sp. f. Haliplidae) Length: 4mm
This tiny (4mm) Haliplidae species carries air bubbles underneath its coxa that covers the ventral surface of its abdomen. It swims by propelling its hairy meta- and prothoracic legs. The two spots at the base of its pronotum identifies the genus Peltodytes. The two spots are absent in the species of genus Haliplus.
Figure 3. Predaceous Diving Beetle (f. Dytiscidae) Length: 9mm
November 1999, Amherst, MA
Predaceous diving beetle is an aquatic beetle that swims with its metathoracic legs. The legs are hairy and widened, and they move simultaneously to swim, which is the characteristics of this family.
Similar looking Hydrophilidae (water scavenger beetles ガムシ科) is not a member of Adephaga and is a Polyphaga species. They differ from Dytiscidae in the length of its long maxillary palps and clavate antenna. Hyrophilidae species swim with alternate movement of their legs and rest with their heads up in the water while Dytiscidae rest with their heads down.
Polyphaga
Shown in the Figure 4 is the ventral view of species of Polyphaga, one of Coccinellidae family (ladybird beetles テントウムシ科). Notice the first abdominal sterna is connected.
Figure 4. Hind Leg (f. Coccinellidae)
Figure 5 shows the tarsus of Coccinellidae. It appears to be three segmented (four segmented really, with a small segment attached to the last segment). The tarsal claw of Coccinellidae is very peculiar -- it is toothed..
Figure 5. Tarsus and Tarsal Claw (f. Coccinellidae)
Figure 6 shows the clavate antenna of Coccinellidae.
Figure 6. Antenna (f. Coccinellidae)
Many of the Coccinellidae species are predaceous and mostly feed on aphids. Chrysomelidae (leaf beetles ハムシ科) is an another family that looks similar to Coccinellidae, which are herbacious. Their antennae are conspicuous, and their claws are simple and not toothed.
Other popular Coleoptera includes Scarabaeidae (scarab beetles, such as rhinoceros beetles and flower beetles コガネムシ科), Lucanidae (stag beetles クワガタムシ科), Curculionidae (snout beetles ゾウムシ科), and Cerambycidae (long horned beetles カミキリムシ科).
Elateridae コメツキムシ科 (Figure 7) is an another member of Polyphaga. It has strong muscles that fills up its thorax enable it to jump in the air, with a snap, when it is laid on its back. This species is called ricecake-making-bug or kome-tsuki-musi because of this behavior in Japan. Its antenna is serrated. Its tarsal segments are 5-5-5. Its white, shiny larvae are called wire-worm (elateriform).
Figure 7. f. Elateridae
(November 2001, Portland, OR), Length: 8mm
Archeostemata and Myxophaga
The other two less common suborders of Coleoptra are Archeostemata ナガヒラタムシ亜目 and Myxophaga ツブミズムシ亜目.