Rain beetle
Encyclopedia
The rain beetles are a group of beetle
s found 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 Geotrupidae, they are currently assigned to their own family Pleocomidae, considered the sister group to all the remaining families of Scarabaeoidea
. The family contains a single extant genus, Pleocoma, and one extinct
genus, Cretocoma, described in 2002 from Late Cretaceous
deposits in Mongolia
.
Of 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. The back is hairless and glossy. Overall color ranges 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 4–8 lamellae, more than in any other group of Scarabaeoidea
. The mandibles
are non-functional, and the opening into the esophagus
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
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
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.
Members of Pleocoma are known from extreme southern Washington, throughout the mountains of Oregon
and California
, and into the extreme north of Baja California
.
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
s found in the far west of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. They spend most of their lives underground, emerging in response to rain or snow, thus the common name. Formerly classified in the Geotrupidae, they are currently assigned to their own family Pleocomidae, considered the sister group to all the remaining families of Scarabaeoidea
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...
. The family contains a single extant genus, Pleocoma, and one extinct
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
genus, Cretocoma, described in 2002 from Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
deposits in Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
.
Of 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. The back is hairless and glossy. Overall color ranges from black to a reddish-brown, while the hairs may range from yellow to red to black. The antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
are 11-segmented, with a club of 4–8 lamellae, more than in any other group of Scarabaeoidea
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...
. The mandibles
Mandible (insect)
Insect mandibles are a pair of appendages near the insect’s mouth, and the most anterior of the three pairs of oral appendages . Their function is typically to grasp, crush, or cut the insect’s food, or to defend against predators or rivals...
are non-functional, and the opening into the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
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
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
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
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 outside the body of the secreting individual to impact the behavior of the receiving individual...
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.
Members of Pleocoma are known from extreme southern Washington, throughout the mountains of Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
and California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, and into the extreme north of Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
.