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Eleodes

Eleodes (commonly known as pinacate beetles or desert stink beetles) is a genus of darkling beetles in the family Tenebrionidae. They are endemic to western North America, ranging from southern Canada to central Mexico, with many species found along the Mexico-United States border. Some species have been introduced to Colombia. The name pinacate is Mexican Spanish, derived from the Nahuatl (Aztec) name for the insect, pinacatl, which translates as "black beetle".

Eleodes species range from about in length and are black, with some having a reddish tint on their abdomen. The setae of some species such as Eleodes osculans collect debris and give the insect a brown color, a similar effect occurs in the species Eleodes mirabilis giving it the appearance of having whitish stripes on its abdomen. Due to the number of species and their large range these beetles have a fairly varied appearance throughout the many species. All produce quinone or similar substances as a deterrent to predators, and many will stand on their heads to spray it. They are typically found in the arid desert regions of their range, but can also be found in forests and grasslands. All Eleodes species are flightless as their elytra are fused together and their second pair of wings is very reduced and vestigial.

Ecology

Most members of the genus Eleodes are primarily detrivores feeding on plant and animal debris. Some species are more inclined to consume living plants, which is especially true for species native to the plains of North America, such as Eleodes hispilabris and Eleodes opaca. The larvae of those species and others are considered pests as they feed on the roots of crops.

Species found in dry regions, such as members of the subgenus Eleodes, are usually much larger than what is expected for most insects, this is due the lack of water in the area leading to these beetles evolving larger bodies in order to hold more of it. Water loss is also the reason that the elytra are fused in Eleodes. As expected, species found in forests, such as members of the subgenus Blapylis, are smaller, closer to the size of most other insects.

Eleodes are generally more active at night; some species are strictly nocturnal while others can and will be active during the day. As these beetles are fairly long-lived for insects, they must adapt to the different seasons. During the fall, they are diurnal as it is warmest during the day. When winter comes, they take shelter and become inactive so as not to freeze in the cold. When spring arrives, they go back to being active during the day until the summer when they switch to being active at night to survive the deadly high temperatures of the desert. Eleodes take shelter almost anywhere that can protect them from the hot and cold. This can be wood or rocks, but is often rodent burrows. Every night when these beetles scavenge for food, they pick a new shelter for the day, which, if not suitable for protection against the elements, will be abandoned in search of a new one. One subgenus, Caverneleodes, lives only in caves, cave-like environments, or rock crevices. These beetles have reduced eyes and only leave their hideouts to scavenge for food.

Chemical defense

Beetles within Eleodes and other genera within Tenebrionidae exude a foul-smelling odor and a very distasteful liquid from glands to ward off predators. This liquid is most commonly a quinone. While not being poisonous the liquid does usually deter predators, the success of this defense mechanism has led to the evolution of a Müllerian mimicry complex among Eleodes acuticauda, Eleodes dentipes, and Coelocnemis magna, the latter of which while not being within Eleodes is a still distasteful prey item. All three previously mentioned species look strikingly similar, leading to a strengthened defense against potential predators. Another Müllerian mimicry complex exists between Eleodes scabrosa and Eleodes tuberculata. The "head-standing" behavior exhibited by these beetles is aposematic. By leaving their presence and identity unambiguous to potential predators, it means that more individuals can survive as predators will avoid beetles with the "head-standing" behavior.

While this defense is generally effective in deterring predators, they are still preyed upon by many species, such as owls, foxes, coyotes, skunks, bats, turtles, etc.

Fossil record and evolution

Fossils of Eleodes acuticauda, Eleodes osculans, Eleodes carbonaria, Eleodes granulata, Eleodes gracilis, and others have been found in the La Brea Tar Pits, Carpinteria Tar Pits, and the Snowmastodon Site which are all dated to the Pleistocene epoch. Eleodes split off from the rest of Amphidorini at least 8 to 15 million years ago in the Miocene, although this estimate is likely on the lower side due to low taxon sampling.

Taxonomy

Eleodes is the largest New World genus of darkling beetles comprising around 200 species divided up into the following 17 subgenera.

<big>Subgenera:</big>

<big>Incertae sedis:</big>

Notes

See also

References

External links