Coleoptera

“If one could conclude as to the nature of the Creator from a study of his creation it would appear that God has an inordinate fondness for beetles”                                                                       -J.B.S. Haldane

The Coleoptera (beetles) are an order of insects that contain more species (>400,000) than another order, comprising 40% of insecta and 25% of all known animals. Some estimates put the number of beetle species at 1 million, but the inaccessibility of tropical habitats and small sizes of the specimens makes describing the entire diversity difficult. The distinguishing characteristics of beetles are hardened hindwings (elytra) incapable of flight, a triangular plate between the wing cases (scutellum) and mandibulate (biting) mouthparts and a large prothorax with a small mesotheroax.

IMPORTANCE. Being such a diverse group of insects, the coleoptera range from being beneficial carnivores that may predate pests (such as ground beetles, ladybirds and rove beetles) to pernicious pests that burrow into or eat roots, flowers, leaves, stems, fruits, trees and even stored grains. Other beneficial beetles include detritivores such as dung beetles that roll up dung and bury it making it unavailable for pestilent flies and parasitic worms that need it to breed. Some beetles are a mix of beneficial and pestilent- dermestids (skin beetles) have been used in taxidermy to clean bones of the remaining skins, but can also be a pest of entomological collections.

CLASSIFICATION. Coleoptera can be divided into 4 suborders: Archostemata, Mxyophaga, Adephaga and Polyphage, the last of which contains 90% of the order’s species. Polyphaga contains more than 170 families, including important families such as Curculionidae (weevils), Staphylinidae (rove beetles), Scarabaeidae (scarab beetles), Lucanidae (stag beetles) and Meloidae (blister beetles). The highly abundant Carabidae family (ground and tiger beetles) belong to the Adephaga suborder. More detailed classification can be found here.

IDENTIFICATION. Adephaga can be distinguished from Polyphaga by several morphological characteristics, such as enlarged trochanters of hind legs in adephaga; immovable metacoxae dividing the 1st abdominal sternite and a medial folding hinge and closed cell in the wing veination. Adephaga larvae are campodeiform whereas polyphaga larvae are various types (including eruciform). An introduction to keying out families can be found through this link.

ADAPTATIONS. Beetles are on of the earliest endopterygote (complete metamorphosis) groups to evolve. They exploited the surface and sub-surface of habitats which led to adaptive radiation. The success of the beetles can be attributed to their diversity in movement (rapid runner, agile climbers and jumpers), protective features (tough cuticle, large jaws, speed, crpytic habits and chemical weapons), mouthparts (mandibulate- bite and can deal with broad range of food) and their efficient cuticle (good at conserving water).

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