The Ground Beetle
There are about 40,000 species of ground beetle alive in the world, and only about 2,000 of those species live in North America and Europe. A large family of beetle, known by the Latin Carabidae, they may be found on every continent except Antarctica. As a result, ground beetles have been subject to the avid fascination of collectors for centuries. Darwin, for example writes enthusiastically about his own collection.
The classification of ground beetles scientifically (or their taxonomy) shares a common base. This is as follows: (Kingdom) Animalaia, (Phylum) Arthropoda, (Class) Insecta, (Order) Coleoptera, (Suborder) Adephaga, (Superfamily) Caraboidea, and (Family) Carabidae. The specification of species and genus, etc. follows on from here. The first documentation of ground beetles (specifically the adephaga) dates them back to 250 million years ago (the Permian period). Evidence suggests that as late as 200 million years ago (Triassic period) they began to separate from near relations and evolve into their own diverse family throughout the Jurassic period. Extensive research has been done to clarify the evolution and taxonomy of this insect family.
While the specifics of their preferred habitat may vary according to where they live, most ground beetles live underneath tree bark, beneath fallen logs, and among the rocks or sand that accumulate along the edge of rivers and other bodies of water, such as ponds or lakes. They thrive in the dark and damp of these spaces.
The bodies of ground beetles are rounded with a black or metallic color, and are often ridged where their protective shell covers their wings (called elytra). This makes it quite easy for them to camouflage themselves among their preferred habitat of rocks and bark. Another reason it is an ideal place for them to live. In some species the elytra, or wing covers, are fused and they are unable to fly. This is especially true of larger species. Species of ground beetle are further distinguishable by a range of characteristics, including the shape of their elytra (as in the case of the violin beetles) or the presence of a groove on their foreleg with a comb of hairs that they use to clean their antennae (as in the case of the flanged bombardier beetle).
Most, though not all, species of ground beetle are carnivorous and nocturnal. They will deliberately hunt down any invertebrate they are capable of overpowering, in some cases running down their prey. The tiger beetle (Cicindelnae) for instance, is capable of maintaining a speed of five miles per hour (8 kilometers per hour), which makes them one of the fastest land animals on the planet in relation to their size. The tiger beetle is also one of the few diurnal beetles, and therefore is more brightly colored and has larger eyes in order to hunt by sight. Another species of ground beetle (known as the promecognathus laevissimus in Latin) specializes in hunting the cyanide millipede (harpaphe haydeniana) and has evolved to counter the millipede’s deadly hydrogen cyanide.
When it comes to defending themselves from predators, ground beetles are very well equipped, though each species in a slightly different way. The majority of them have well developed pygidial glands toward the back of their underbelly. These allow them to release noxious, even caustic secretions that ward off potential predators.
In some cases, like the bombardier beetles, the secretion is mixed with more volatile compounds to produce a small combustion. This might create small popping sound, or a cloud of acrid gas. The gas can be potent enough to kill invertebrate predators out right, causing injury to small mammals such as mice or shrews. For humans, it is just a highly unpleasant experience. Interestingly, however, the ability to “bomb” predators occurred twice in the evolution process as there are two species of beetle that are capable of doing so: the flanged bombardier beetles (grouped among the most ancient ground beetles) and the more typical bombardier beetles or Brachininae (these are of a more modern lineage).
Of course this isn’t the only way that ground beetles have evolved to defend themselves. Separate from the bombers in their self-defense, are the squirting beetles. The South African anthiini beetles are capable of squirting their secretions over quite a distance.
The relationship between humans and ground beetles is generally a positive one. As a predatory invertebrate, feeding on many that are considered to be pests, ground beetles are generally considered beneficial. In some cases they have even been shipped internationally as a pest control effort. The C. sycophanta, commonly known as the Forest Caterpillar Hunter, for example, was brought over to New England from Europe as early as 1905 as a form of biological pest control for the gypsy moth, rather than employing pesticides or other toxic chemicals; a method that continues to be employed as gypsy moths have spread further into the North American continent over the past century.
There are, however, a few species that are considered to be pests. The zabrus, for example, is one of the few herbivorous beetles that have been known to do damage to crops on occasion (in particular the zabrus tenebrioides on these occasions). More generally ground beetles are viewed as pests only if they are present in large numbers. In these instances they can become obnoxious to humans during outdoor activities like camping or a cook out. The latter especially if they get into the food because when they release their defensive secretions the foodstuffs are ruined.
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