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Scarabaeidae Latreille, 1802
SCARAB BEETLES
Scarabs; Dung beetles; Flower beetles; Rain beetles; Tumblebugs

Life   Insecta   Coleoptera

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Anomala orientalis
© Copyright Hadel Go 2014 · 9
Anomala orientalis
Popillia japonica, -unknown, -back 2012-07-24-14.55.07-ZS-PMax
© Copyright source/photographer · 9
Popillia japonica, -unknown, -back 2012-07-24-14.55.07-ZS-PMax

Pelidnota punctata, Grapevine beetle
© John Pickering, 2004-2017 · 8
Pelidnota punctata, Grapevine beetle
Anomala orientalis
© Copyright Hadel Go 2014 · 7
Anomala orientalis

Pelidnota punctata, Grapevine Beetle
© Copyright John Ascher, 2006-2014 · 6
Pelidnota punctata, Grapevine Beetle
Pelidnota punctata, Grapevine Beetle
© Copyright Sheryl Pollock 2011 · 6
Pelidnota punctata, Grapevine Beetle

Popillia japonica, Japanese Beetle
© Copyright Sheryl Pollock 2011 · 5
Popillia japonica, Japanese Beetle
Onthophagus, M, Side, MD, Charles, Indian Creek NRMA ---.. ZS PMax
© Copyright source/photographer · 5
Onthophagus, M, Side, MD, Charles, Indian Creek NRMA ---.. ZS PMax

Onthophagus, M, Side, MD, Charles, Indian Creek NRMA ---.. ZS PMax
© Copyright source/photographer · 5
Onthophagus, M, Side, MD, Charles, Indian Creek NRMA ---.. ZS PMax
Popillia japonica, unknown, face ---.. ZS PMax
© Copyright source/photographer · 5
Popillia japonica, unknown, face ---.. ZS PMax

Popillia japonica, unknown, side ---.. ZS PMax
© Copyright source/photographer · 5
Popillia japonica, unknown, side ---.. ZS PMax
Popillia japonica, unknown, face ---.. ZS PMax
© Copyright source/photographer · 5
Popillia japonica, unknown, face ---.. ZS PMax

Popillia japonica, unknown, side ---.. ZS PMax
© Copyright source/photographer · 5
Popillia japonica, unknown, side ---.. ZS PMax
Popillia japonica, unknown, face ---.. ZS PMax
© Copyright source/photographer · 5
Popillia japonica, unknown, face ---.. ZS PMax

Popillia japonica, Japanese beetle, mating
© John Pickering, 2004-2017 · 1
Popillia japonica, Japanese beetle, mating
Kinds
Overview
The sacred scarab of the ancient Egyptians, Scarabaeus sacer, which inhabits North Africa, southern Europe and Asia, is often the only species of dung beetle that many people know about. We too often overlook the sizeable dung beetle faunas that inhabits our own continents. Indeed, a little observation in the natural habitats of almost any region of the world will reveal several intriguing species of diverse appearances and behaviors .

The Scarabaeinae, one of the two subfamilies of dung-rolling beetles (the other being the Aphodiinae), comprises about 4500 known species of worldwide distribution, occurring wherever excrement or nutrient-rich substrates are available. About 75 species of Scarabaeinae occur in North America (Borror et al., 422; Ratcliffe 95). Scarabaeine diversity is concentrated in the tropics: for example, while the most scarab-rich site in New York State might have close to 10 species, single sites in the tropics can have nearly 100 species. Most species feed on mammal dung, while smaller proportions feed on carrion or vegetable matter, or are even carnivorous. Dung beetles, together with their saprophagous (decay-feeding) relatives, are ecologically important degraders and re-distributors of nutrients.


Identification
Both the taxonomy and the identification of dung beetles may be confusing because they belong to a large group of similar-looking beetles, the Scarabaeidae. This superfamily includes leaf chafers (Rutelinae), June beetles (Melolonthinae), Hercules and rhinoceros beetles (Dynastinae) and many other flower- and fruit-feeders, as well as several groups more closely related to the Scarabaeinae that feed on detritus, carrion, mushrooms, or other decaying material.

The North American Scarabaeinae may be distinguished from other dung beetles and chafers by the following combination of characters (Ratcliffe, 93-94):

  • 1) Clypeus extends over mouthparts, hiding them from above; clypeus often notched or concave along front edge
  • 2) 8 or 9 antennal segments (antennomeres), with 3-segmented club
  • 3) Bases of middle legs far apart from each other
  • 4) Pygidium (end of abdomen) exposed, not covered by elytra
  • 5) A single spur occurs at the tip of the hind tibiae (except for Melanocanthon, which has two spurs)
  • 6) The North American species have the scutellum hidden under the elytra, so that the elytra meet the pronotum in a T-shape. (Some Ataenius and Glaresis have small scutella, and in Cotinus, a wedge-shaped extension of the pronotum conceals the scutellum)

"How do I know what it is?" B. Ratcliffe and M. L. Jameson's key to global Scarabaeoidea:

Tribes in the Scarabiinae, with rough distributions and nest-making habit, after Cambefort, 1991. An asterisk (*) signifies that the tribe is represented in temperate eastern North America.

TribeDistributionHabit
Canthonini * Worldwide Rollers
Eucraniini South America Rollers
Eurysternini South America to southern Mexico Rollers
Gymnopleurini Africa and Asia Rollers
Scarabaeini Old World Rollers
Sisyphini Old World and California Rollers
Coprini * Worldwide Tunnelers
Dichotomiini* Worldwide Tunnelers
Oniticellini Old World, California, Mexico, West Indies Tunnelers
Onitini Africa and Asia Tunnelers
Onthophagini * Worldwide Tunnelers
Phanaeini * New World Tunnelers

The subfamily Scarabaeinae, like the family Scarabaeidae in general, has been divided up in various ways over the years. A classification such as the above is necessary for us to understand and communicate about the world's large and often bewildering variety of dung beetles. However, the classifications have traditionally been based either on personal intuition (not based on a phylogeny, i.e. an evolutionary tree deduced from morphological and/or genetic data) or based on a phylogeny deduced from a narrow set of data, such as genitalic structure. Some recent studies (e.g., Philips et al. 2004) that use larger amounts of information and improved methods of phylogeny reconstruction are now addressing the problem of simplistic and unstable taxonomies. When the results of these continuing evolutionary studies agree on a general phylogeny, the subfamily's natural subgroups (tribes, genera and intermediate levels) will become clear. In the meantime, the traditional classification distinguishes five tribes of scarabaeines in our area: Canthonini, Dichotomiini, Coprini, Phanaeini, and Onthophagini.

Canthonini have slender middle and hind tibiae (whereas the others' tibiae flare distally), and they lack horns or projections of the head and pronotum. Local genera include Canthon, Melanocanthon, and the large-bodied Deltochilum in the Southeast.

The species traditionally classified in the tribes Dichotomiini and Coprini usually have distinct elytral striae and a distinct third segment of the labial palps. Horns on the head and pronotum are not uncommon. Local genera: Ateuchus, Copris, Dichotomius. (On a worldwide scale, both of these tribes, as well as the Canthonini, may prove to be unnatural groupings; Philips et al. 2004).

Phanaeini, represented locally by Phanaeus, lack claws on their tarsi and even lack tarsi on their front pair of legs. Many are metallic green, blue, or other colors.

Onthophagini in North America also may have horns, but their third labial palpomere and elytral striae are relatively indistinct, and their elytra have at least a few small hairs. The tribe is represented by Onthophagus, a large genus (more than 1500 species worldwide) of small- to medium-sized beetles. ( Smith 2003) lists 42 species in the Nearctic realm and northern Mexico.


Geographic distribution

Natural history
Nutrition
Feeding on dung, carrion, fungi and highly organic soil have been interchangeable in the course of this group's diversification. In particular, coprophagy (dung-feeding) has traditionally been held to be a derived (non-ancestral) trait in the Aphodiinae and a "primitive" or "ancestral" trait in the Scarabaeinae. However, a more recent hypothesis (Philips et al., 2004) suggests that certain mushroom-feeding species were the earliest-diverging scarabaeines (nearest to the base of the subfamily's tree) and that coprophagy evolved later. Undoubtedly, many other Scarabaeinae have secondarily switched to feeding on carrion, mushrooms or soil ( Halffter and Edmonds, 11).

The adults and larvae actually feed on the organic colloids and microorganisms in their food. The dung-rolling species construct food balls (for their own consumption), and brood balls for burial and oviposition, within each of which a single larva develops. Many larval scarabs, like cattle, harbor colonies of microorganisms in an expanded region of their digestive tract; these break down cellulose and help digest other components of the food, and the larva in turn digests these microorganisms.

Life Cycle and Population Dynamics
The traits for which scarabs are best known, their nesting behaviors, are diverse and complex. Whereas many species (especially aphodiines) nest and develop inside dung pats, the behavior of sequestering dung balls entails several other unique habits. Since dung pats, relatively speaking, are ephemeral islands of nutrients, they are a textbook case of resource competition and degradative succession. In resource (or "scramble") competition, individuals compete for a pool of non-renewable resources. The total diversity of dung-feeding species in a field of dung pats depends on how well a few species (such as large scarabs) can monopolize the dung, how much species compete with one another versus how much their members compete among themselves, whether the members of each species are clumped or spread evenly among the pats, and whether predators exist that seek out such aggregations of individuals (Hanski 1991). In degradative succession, a pool of resources is broken down by a sequence of species. For example, in the related area of carcass degradation, the first species strip the fresh meat, and the very last species consume the dry hide, hair or feathers. (The related trogid scarabaeoids, or the "skin beetles," consume dry hide, hair and feathers. See U. Nebraska Entomology's Trogidae.) Dung-sequestering scarabs--those that remove and bury dung fragments--come early in the sequence and are especially important competitors because they can monopolize the resource and pre-empt the sequence of other degraders. This behavior makes dung beetles useful for controlling the populations of dung-breeding flies in areas to which non-native livestock have been introduced. The absence of scarabs capable of dealing with cattle manure in Australia and western North America, where cattle have been introduced, has prompted the experimental introduction of several African Onthophagus species. Some of these have proven capable of reducing the populations of flies that serve as vectors for cattle parasites and diseases. The adults of some species (such as Onthophagus striatulus) may also feed on odiferous matter such as decaying mushrooms or carrion, which, like dung pats, are patchy and evanescent in distribution.

The patchiness of their resource necessitates that dung beetles have a strong sense of smell, which is based in their antennae. Their lamellate (book-like) antennal clubs provide ample surface for olfaction. (See U. Nebraska Entomology's Scarabaeoidea Key for images.) Adults generally track a scent plume in flight, land near the dung, and crawl to it (a behavior that facilitates pitfall trapping). Having attained their goal, scarabaeines may bury dung in tunnels dug beneath the pat (such as Onthophagus), roll dung balls away for burial at a distance, or nest inside the pat itself (endocoprid behavior). "Tumblebugs," the larger Canthon species, best exemplify dung-rolling among North American native species; an individal rolling a half-inch pill along a roadside is not an uncommon sight in rural places. Most male and female scarabs that create more than the simplest nests join in monogamous pairs after little if any courtship (Halffter and Edmonds, 63-64) and cooperate to dig the tunnels; the females tend to do more of the nesting work proper, while the males tend to excavate and provision only. Nevertheless, there is a great deal of variation in nesting behavior. Copris and Phanaeus are examples of North American genera that pair monogamously.

Clutch size is often small, which is unusal among insects. For example, Copris species average three to four eggs per brood (but up to 20). Having a smaller number of offspring allows the parents to put more energy into ensuring the survival of each one. The eggs are often very large relative to the female's body, with egg length averaging 1/3 of body length (Halffter and Edmonds 29). The mortality of the young (by predation or disease) is necessarily low, since the larvae develop in a hidden, protected, nutrient-rich environment. Still, other scarab species can lay large numbers of eggs. In the North American fauna, the species introduced to consume cattle manure (such as Onthophagus gazella, which can lay up to 200 in experimental conditions) were chosen for this trait ( Halffter and Edmonds 29).

In general, scarabaeine larvae conform to the typical scarabaeoid "white grub" or "C-grub" habitus: they are pale and hunched in a "C," usually with the abdominal segments dorsally inflated in a distinct hump and the end of the abdomen flattened. These features help the larva maneuver itself in its cell in the dung ball. The immobile pupae, the stage of metamorphosis between larva and adult, often have spines and extensions that keep the rest of the body out of contact with the dung.

Because the larvae are protected, the adults experience more pressure from natural selection. Halffter and Edmonds (25-29) recognize several sources of mortality that put selective pressure on the adults, including random weather variation, the patchy and unpredictable distribution of dung pats, and the fast rate at which dung pats dry out (scarabs need fresh dung, so they must locate it in a time window). Other selective forces are density-dependent: that is, selective pressure increases with population density. These include disease and predation (especially in the tropics) and competition for food and nesting space. Scarabaeinae thus tend to specialize to a certain degree. The species' distributions are most strongly influenced by vegetational ground cover (e.g., desert, grassland, forest) and local climate, which determine the rate at which dung dries out, and the soil type, which influences what kinds of nests can be dug (Halffter and Edmonds, 13). Less common is narrow specialization on excrement from specific animals, such as rodents or carnivores. A few exotic species cling to particular hosts, such as sloths, tapirs, wallabies or even large snails (Balthasar, 57). Onthophagus orpheus inhabits the burrows of mammals, and Onthophagus polyphemi and Copris gopheri in Florida dwell in the tunnels of the burrowing tortoise, Gopherus polephemus. Some North American aphodiines specialize in deer droppings (see Aphodiinae).


How to encounter
In the Eastern United States, the highest diversity of dung beetles seems to usually be found in sunny, sandy areas (although collecting in different habitats will yield interesting results). As you go from south to north, or from the coast inland (and to higher elevations), diversity generally decreases. North of Massachusetts, there are only a handful of Onthophagus and Copris species to be found, whereas in the Carolinas down to Florida, a variety of large and often colorful Phanaeus (which can be collected as far north as Massachusetts) and Canthon await the collector, as well as many smaller species. Sandy pine and oak forests and scrubby areas are good places to look for dung beetles, and soft sandy soil is easy to dig in. Actually, "looking" for dung beetles is usually not terribly productive. Flipping over cattle dung in pastures may seem intuitively like a good way to find dung beetles, but this method is rarely successful. Baited pitfall traps are the standard dung beetle sampling method. Human (considered to be the best) or pig dung is placed in a small cup or in a mesh bag and suspended inside a can or jar which is dug into the ground. Water with soap can be put in the bottom of the trap (to drown the beetles and prevent them from escaping). More elaborate flourishes can include a rain guard (which can be a rectangular piece of cardboard arched over the can and staked into the ground on either end), some kind of guard to keep out rodents and other animals (a steel mesh square of a preferred gauge is used to cover the trap and the four corners are staked into the ground to secure it), etc. As dung beetles are habitat-specific, setting traps only meters apart between bordering habitats can yield very different species. The drawback to pitfall collecting is that it, like light-trap collecting, yields high numbers of specimens but little ecological data (such as what the species actually eat, or what they provision their larvae with). However, it is a good way to determine presence or absence of different species.


Links to other sites

References


Acknowledgements
We would like to thank Sacha Spector for his reviews and Brett Ratcliffe and Mary Liz Jameson for advice.
  • Jim Hayden, Dept. of Entomology, Cornell University and American Museum of Natural History
  • Kyle Beucke, Dept. of Invertebrate Zoology, American Museum of Natural History
  • Stephanie Westergren, Dept. of Entomology, University of Nebraska
  • John Pickering, University of Georgia, Athens

Supported by

Hosts · map
FamilyScientific name @ source (records)
Asclepiadaceae  Asclepias syriaca @ PN- (1)
Asteraceae  Achillea millefolium @ PN- (1)
Fabaceae  Trifolium pratense @ PN- (3)

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Updated: 2018-01-23 08:28:40 gmt
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