Coleoptera
Coleoptera is the largest order which consists of 35% (290,000 out of 840,000 insects and related species worldwide) of all the species of the class Insecta. Its hardy elytra cover the abdomen. Its Japanese name is kou-chu, or armor-bugs. Elytra are often brightly colored as is the case with ladybird beetles shown in Figure 1.
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 (Figure 2. コガシラミズムシ科) and Dytiscidae (Figure 3. ゲンゴロウ科) are aquatic beetles.
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.
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 5 shows the tarsus of Coccinellidae. It appears to be three segmented yet four segmented really, with a small segment attached to the last segment. The photo shows a small projection on the tarsal claw of Coccinellidae.
The photo below shows the clavate antenna of 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).
Archeostemata and Myxophaga
The other two less common suborders of Coleoptra are Archeostemata ナガヒラタムシ亜目 andMyxophaga ツブミズムシ亜目.