''Pleocoma'' is the only

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

genus of rain beetles (family

Pleocomidae The rain beetles are a group of beetles whose extant species are found only in the far west of North America. They spend most of their lives underground, emerging in response to rain or snow, thus the common name. Formerly classified in the Scara ...

) and is endemic to the Pacific states of North America. Fossil remains of ''Pleocoma'' have been found in the

Yixian Formation The Yixian Formation (; formerly Romanization of Chinese, transcribed as Yihsien Formation or Yixiang Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the Barremian stage of the Early Cretaceous. I ...

in China, suggesting beetles in this genus have existed in something like their present form since at least the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period. There are 27 described species in ''Pleocoma''. Possessing a robust oval body form similar to other scarabaeiforms, their ventral side is densely covered with fine, long hairs (genus name derives from Greek (', abundant) and (', hair), extending to the legs and to the margins of thorax and

elytra An elytron (; ; : elytra, ) is a modified, hardened forewing of beetles (Coleoptera), though a few of the true bugs (Hemiptera) such as the family Schizopteridae are extremely similar; in true bugs, the forewings are called hemelytra (sometime ...

. The back is hairless and glossy. Overall colors range from black to a reddish-brown, while the hairs may range from yellow to red to black. The antennae are 11-segmented, with a club of four to eight lamellae, more than in any other group of the

Scarabaeoidea Scarabaeoidea is a superfamily of beetles, the only subgroup of the infraorder Scarabaeiformia. Around 35,000 species are placed in this superfamily and some 200 new species are described each year. Some of its constituent families are undergo ...

. The

mandibles In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

are not functional, and the opening into the

esophagus The esophagus (American English), oesophagus (British English), or œsophagus (Œ, archaic spelling) (American and British English spelling differences#ae and oe, see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), c ...

is closed off; adults do not eat. Larvae have the typical scarabaeiform characteristics, C-shaped bodies generally a creamy white. They feed on roots in the soil, often deep beneath the host plant. Details of the larval stage are only known for some species; they have nine or more

instar An instar (, from the Latin '' īnstar'' 'form, likeness') is a developmental stage of arthropods, such as insects, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...

s, and may take up to 13 years to mature. After a late summer pupation, adults of both sexes dig their way to the surface, emerging around the onset of the fall/winter rainy season typical of, for instance, California's climate; some species are active as late as early spring. Females have only vestigial wings, so the males fly around (often while it is raining), homing in on

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

s released by the females. They mate on the surface or in a burrow dug out by the female, then the female lays eggs in the bottom of the burrow. The "triggering" conditions required for some species to fly are so stringent that a given population may only be active for a single day in a given year. Males are commonly attracted to bright lights.

Species

Fossil species

* †'' Pleocoma dolichophylla'' Nikolajev & Ren, 2012

Species

Fossil species

References

Further reading