Rhinoceros beetle characteristics, habitat, behavior

1334
Robert Johnston

Rhinoceros beetle is the common name for the species that are part of the Dynastinae subfamily. The insects that make up this group are characterized by their large size and physical appearance, where the large horns stand out..

These coleopterans are distributed throughout the world, except in the polar areas. Regarding their habitat, they prefer humid tropical forests and mature forests.

Rhinoceros beetle. Source: Weimar [Public domain]

In such ecosystems, the rhinoceros beetle lives among decayed stems and leaves, on which it feeds. In addition, the adult usually eats fruits, leaves and roots.

In relation to its reproduction, it is sexual. The unicorn beetle, as it is also known, undergoes a complete metamorphosis. Thus, it goes through the stages of egg, larva, pupa to finally become an adult, capable of mating.

Article index

  • 1 General characteristics
    • 1.1 Body
    • 1.2 Size
    • 1.3 Coloring
    • 1.4 Head
    • 1.5 Horns
  • 2 The evolution of the horn
  • 3 Conservation status
  • 4 Habitat and distribution
    • 4.1 Geographical location of some species
    • 4.2 Habitat
  • 5 Taxonomy and subspecies
    • 5.1 - Taxonomy
    • 5.2 - Tribes
  • 6 Food
  • 7 Playback
  • 8 Behavior
  • 9 References¬†

General characteristics

Body

The body of the adult rhinoceros beetle is covered by a thick exoskeleton. In addition, it has a pair of thick wings, known as elytra. Below these, it has other wings, of the membranous type. These allow the beetle to fly, although it does not do so efficiently due to its large size..

The claws of the tarsus are almost all the same size. The exception to this characteristic is present in the males of some Pentodontini. In these, the pro tarsal claws are notably enlarged.

Size

The size of the species that make up the Dynastinae subfamily is very varied. However, in general they can grow up to 18 centimeters. Thus, one of the smallest is the American rhinoceros beetle (Xyloryctes jamaicensis), which is between 25 and 28 millimeters long.

The largest of the clade is the hercules beetle (Dynastes hercules), which has a total length of 18 cm, of which approximately 10 centimeters correspond to the horn.

Coloration

Due to the great diversity of species, the range of colors of the rhinoceros beetle is very wide. Some may be brightly colored, with iridescent and metallic hues. Others are black, green, gray, or dark brown. In addition, its body may be covered with hair, thus giving it a velvety appearance..

On the other hand, in certain insects, such as the hercules beetle, the color of the male varies, depending on the humidity level of the environment that surrounds it..

Thus, in the case that the atmosphere is dry, the elytra have a yellow or olive green hue. These turn black, when the humidity rises considerably. The mechanism associated with these changes in tonality is related to the internal structure of the elite..

Head

In the rhinoceros beetle, the upper lip or labrum is hidden under a shield-shaped structure, known as the clipeus. In relation to the antennas, these have between 9 or 10 segments. Usually the last three form a single structure.

Regarding the dentition, the presence varies among the members of the subfamily. For example, members of the Cyclocephalini tribe do not have mouthparts on the lateral edge of their jaws. In contrast, the species of the Phileurini tribe have teeth.

Horns

The horns of the rhinoceros beetle project as rigid cuticular growths. These are born from the prothorax and / or the head. Regarding its development, it occurs from the epidermal tissue of the larvae, which later proliferates, forming a disk.

The three-dimensional shape of the adult horn originates from a structure of several dermal folds. These unfold as the beetle passes from the larval stage to the pupa..

The size and shape of the male's horn is variable. Thus, the rhinoceros beetle has two horns, one thoracic and the other cephalic, which resemble tweezers..

Another striking species is the elephant beetle. This has a large central horn on its head, the end of which is divided in two. On the sides of the thorax, two shorter conical horns project.

The growth of this structure is affected by various factors, among which is food. According to various investigations carried out, the development of the horns is highly influenced by the physiological and nutritional state of the animal.

Experts point out that these structures are used during contests between males, due to the option of mating with the female. These aggressive interactions are not intended to cause injury to the opponent, but rather to force him away from the area..

In the following video you can see the development of the Hercules beetle (Dynaster hercules), a subspecies of rhinoceros beetle:

The evolution of the horn

The Scarabaeidae family is made up of approximately 35,000 species. Of these, the vast majority do not have horns. However, some complete families have such structures. In this sense, the specialists propose a hypothesis that supports the presence of the horns in these clades.

The approach suggests that the horns existed before the beetles diversified. Thus, experts maintain that there are indications that suggest the presence of this structure in the ancestors of this insect..

One of these is that the vast majority of the hornless subfamilies have at least one species with rudimentary horns, as in the case of the Pleocomidae and Ochodaeidae families..

In addition, some beetles in the pupal stage develop structures similar to thoracic horns. This would be an indication that the adult ancestors probably had these antlers.

If this hypothesis is true, it means that the lack of horns in most current beetles is a condition that implies the suppression of the growth of said structure..

State of conservation

Some of the rhinoceros beetle populations are threatened with extinction. Such is the case of Calicnemis latreillei, which has been categorized by the IUCN as a species at risk of disappearing from its natural habitat.

This beetle lives in Algeria, France, Italy and Spain. In these regions, the environment is degraded, due to logging and deforestation of the forests. In addition, forest lands are used to build urban elements and tourist structures..

Regarding conservation actions, several of the areas where the Calicnemis latreillei are under the protection of national and international organizations.

On the other hand, some species, such as the hercules beetle (Dynastes hercules), they lack sufficient data to know their state of conservation.

However, the rainforests where they live are fragmented and degraded, due to the action of climate change and deforestation. In addition, a large number of species of the Dynastinae subfamily are captured, to be sold internationally as pets..

These factors affect the communities of this insect, and may have a negative impact on its development..

Habitat and distribution

Rhinoceros beetles are widespread on all continents, with the exception of the polar regions and Antarctica. Although its distribution is very wide, the highest population density is found in the tropics.

Geographical location of some species

Rhinoceros beetles that live in the United States are found southward, from northeastern Arizona to the state of Nebraska..

Numerous populations inhabit Central America. For example, in Panama and Costa Rica there are around 157 species, many of which have been recently described. Such is the case of Cyclocephala amazona, C. labidion, C. mustacha Y C. stockwelli.

In Guatemala and Honduras there is Maya dynastes. Likewise, the cornizuelo (Megasoma Elephas) lives from southern Mexico to northern Venezuela and Colombia.

In relation to South America, it extends widely throughout all the tropical regions of the continent. Thus, the Enema bread lives in the Cerrado-Pantanal ecotone (Mato Grosso, Brazil).

Another South American species is the Actaeon beetle (Megasome acteon), found in Bolivia, Colombia, Brazil, Ecuador, Guyana. Peru, Panama, Venezuela and Suriname.

Some of these coleopterans have a much more extensive distribution, such as the European rhinoceros beetle (Oryctes nasicornis). It lives in Europe to the central region of the Scandinavian Peninsula, North Africa, Western and Central Asia.

In contrast, the canary rhinoceros beetle (Oryctes prolixus) is located only in the western islands of the Canary archipelago.

Habitat

Due to its extensive range, the habitats are very diverse. These include humid forests, tropical forests, lauraceous forests, oak forests and lowlands..

In such ecosystems, the rhinoceros beetle lives in the decomposed wood of shrubs and trees. Also, it can be found between the roots or between the stems of palm leaves..

Fallen logs and litter provide the insect with a safe hiding place. In this, you can take shelter during the day, to protect yourself from the threats of your predators.

For some species, such as the Megasoma elephas, lowland wooded areas are a suitable environment for their development.

However, they prefer mature forests. The reason for this is that these ecosystems have a large number of plant species, which are absent in younger forests..

Furthermore, in mature wooded areas there are large amounts of dead logs on the ground and standing, which are in various states of decomposition.

These constitute an ideal environment for the nesting and growth of the larvae, which feed exclusively on this plant material..

Taxonomy and subspecies

- Taxonomy

-Animal Kingdom.

-Subkingdom: Bilateria.

-Infra-kingdom: Protostomy.

-Superfilum: Ecdysozoa.

-Phylum: Arthropoda.

-Subphilum: Hexapoda.

-Class: Insecta.

-Subclass: Pterygota.

-Infraclass: Neoptera.

-Superorder: Holometaball

-Order: Coleoptera.

-Superfamily: Scarabaeoid.

-Family: Scarabaeidae.

-Subfamily: Dynastinae.

- Tribes

Agaocephalini

Members of this tribe have horns or tubercles on the head and on the pronotum. In addition, they have a wide jaw, which may or may not have teeth. The elytra have an irregular stippling.

Regarding its distribution, it is found in the tropical regions of the New World, where there are 11 genera and approximately 40 species..

Cyclocephalini

This tribe is made up of 13 genera, which are restricted to the New World, with the exception of the monobasic genus Ruteloryctes, which is in Africa.

The legs of this beetle have cylindrical tarsi, while in almost all species the anterior tarsi are enlarged. In relation to the jaws, they lack teeth.

Dynastini

This tribe is made up of three genders, which inhabit the New World. The members of this clade are within the group of the largest insects on Earth.

Males generally have horns on the head and on the pronotum. As for the females, the vast majority do not have a horn, but they could have tubercles on the head..

Oryctini

The males of this tribe have horns or tubercles on the head and on the pronotum. As for females, the pronotum generally has a fovea. The jaws have teeth or lateral lobes. The end of the posterior tibia has numerous shallow notches.

The Oryctini tribe is distributed worldwide, with the exception of the poles. In the New World there are a total of 13 genera.

Pentodontini

Pentodontini is the largest tribe in the Dynastinae subfamily, with a total of 25 genera in the New World. The species that compose it are widely extended in the world, less in the polar regions.

One of the characteristics of the members of this clade is that the head and pronotum have tubercles or ridges. In relation to the jaws, they have 1 to 3 teeth or lateral lobes.

Phileurini

The head has short horns or tubercles, while the pronotum is grooved and usually has an apical protrusion. Some species may have teeth, while others lack teeth. Regarding their location, a large part of these are found in tropical areas worldwide..

Feeding

Rhinoceros beetles are herbivorous animals. The diet varies according to the stage of development in which the insect is. Thus, the larvae feed on decomposing plant matter, such as litter and decomposed wood, among others..

Adults have a more varied diet. Depending on the species, they can feed on fruits, either fresh or decomposed, nectar and tree sap. Others eat from the roots of plants that are in a state of putrefaction..

Contrary to their large size, adult species do not ingest large amounts of food, unlike larvae, which eat abundantly and almost constantly.

On the other hand, they usually feed at night, since during the day they hide among the branches and fallen leaves, with the intention of hiding from predators..

Here you can see how a specimen feeds on a piece of orange:

Reproduction

Like the rest of the Scarabaeidae family, the rhinoceros beetle reproduces sexually. In addition, it has a complete metamorphosis, with four stages: egg, larva, pupa and adult..

In the breeding season, the males compete with each other for the right to mate with the female. In these combats, the male seeks to dominate the adversary using his horns.

Thus, the hercules beetle takes the opponent between its two antlers, which resemble pincers, and lifts him off the ground. He then throws it into the air, causing it to fall heavily. This he does repeatedly, until the other male leaves the area. The winner can mate with several females, during the same reproductive period.

After copulation, the female lays the eggs in a closed, dark area, close to the decomposed plant matter. In this way, when the eggs hatch, the larvae can feed on the humus.

Some species take a long time to reach adulthood. For example, the larvae of the genus Megasoma, where the elephant beetle (Megasoma elephas), it can take three to four years to become adults.

In the following video you can see the mating of two specimens:

Behaviour

The rhinoceros beetle is a nocturnal animal. If the insect feels threatened, it may make a loud, shrill sound. This occurs when you rub the elytra against the abdomen.

Some species of the Dynastinae subfamily, such as the Trypoxylus dichotomus, it exhibits a behavior of carving the bark of the tree, in order to feed on its sap. For this, use the small projections of the clipeus.

However, other insects of the same clade, among which are Dynastes hercules Y T. dichotomus, use their jaws to break the trunk, instead of the protrusions of the clipeus.

Also, some adults use only one side of the jaw. Experts point out that this may be because the beetle tries to avoid breaking this structure. This could occur if the animal transfers food from one jaw to the other..

References

  1. Wataru Ichiishi, Shinpei Shimada, Takashi Motobayashi, Hiroaki Abe. (2019). Completely engaged three-dimensional mandibular gear-like structures in the adult horned beetles: reconsideration of bark-carving behaviors (Coleoptera, Scarabaeidae, Dynastinae). Recovered from ncbi.nlm.nih.gov.
  2. Takahiro OhdeI, Shinichi Morita, Shuji ShigenobuI, Junko Morita, Takeshi Mizutani, Hiroki Gotoh, Robert A. Zinna, Moe Nakata, Yuta Ito, Kenshi Wada, Yasuhiro Kitano, Karen Yuzaki, Kouhei Toga, Mutsuki MaseI, Kojima KusadotaI, Kojima RusadotaI, Kojima RusadotaI Laura Corley Lavine, Douglas J. EmlenI, Teruyuki NiimiI
  3. (2018). Rhinoceros beetle horn development reveals deep parallels with dung beetles. Recovered from ncbi.nlm.nih.gov.,
  4. Wikipedia (2020). Dynastinae. Recovered from en.wikipedia.org.
  5. The National Wildlife Federation (2020). Rhinoceros Beetles. Recovered from nwf.org.
  6. Lawrence, J. F. and A. F. Newton. (nineteen ninety five). Families and subfamilies of Coleoptera (with selected genera, notes, references and data on family-group names). Recovered from unsm-ento.unl.edu.
  7. Encyclopaedia britannica. (2020). Rhinoceros beetle. Recovered from britannica.com.
  8. Hadley, Debbie. (2020). Rhinoceros Beetles, Subfamily Dynastinae. ThoughtCo. Recovered from thoughtco.com.
  9. Ed Yong (2014). Rhino Beetle Weapons Match Their Fighting Styles. Recovered from nationalgeographic.com.

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