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"A spectacular sampling of the more than 350,000 species of beetles on earth. . . . The book is not only an excellent reference, but a joy to peruse."
The Book of Beetles celebrates the beauty and diversity of this marvelous insect. Six hundred significant beetle species are covered, with each entry featuring a distribution map, basic biology, conservation status, and information on cultural and economic significance. Full-color photos show the beetles both at their actual size and enlarged to show details, such as the sextet of spots that distinguish the six-spotted tiger beetle or the jagged ridges of the giant-jawed sawyer beetle. Based in the most up-to-date science and accessibly written, the descriptive text will appeal to researchers and armchair coleopterists alike.
The humble beetle continues to grow in popularity, taking center stage in biodiversity studies, sustainable agriculture programs, and even the dining rooms of adventurous and eco-conscious chefs. The Book of Beetles is certain to become the authoritative reference on these remarkably adaptable and beautiful creatures.
WHAT IS A BEETLE?
The English word "beetle" comes from the Middle English bityl or betyll and the Old English bitula, all of which mean "little biter." Other commonly used names, such as "weevil" and "chafer" derived from Old English and Old High German, also relate to biting. Coleoptera, first coined by Aristotle in the fourth century bce and later adopted as an order of insects by Carl Linnaeus in 1758, is derived from the Greek words koleos, meaning "sheath," and pteron, or "winged," and was inspired by the tough elytra of beetles.
Among other adaptations, beetles are distinguished from other insects by their chewing mouthparts, the conversion of their forewings into hardened elytra, their hind wings that fold lengthwise and across beneath the elytra, and their holometabolous development. Holometabolous insects pass through four very distinct life stages: egg, larva, pupa, and adult. The larvae and adults frequently differ in habits and habitat, functioning in the environment as if they were two separate species.
Beetles, like other insects, crustaceans, arachnids, millipedes, centipedes, and their kin with segmented exoskeletons and jointed appendages (antennae, mouthparts, legs), are classified in the phylum Arthropoda. Light and durable, the beetle exoskeleton is incredibly tough and rigid or characteristically soft and pliable, and provides protection and support. It serves as a platform for important tactile and chemosensory structures externally, while providing an internal framework that supports muscles and organs. The exoskeletal surface is smooth and shiny, or dulled by waxysecretions or microscopic networks of cracks (alutaceous) resembling that of human skin. The surface is variously festooned with spines, hairlike setae, or flattened setae called scales, and sculpted with tiny bumps (tubercles), pit-like punctures, ridges, grooves (striae), or rows of punctures.
The colors of beetles are derived either from chemical pigments obtained from their food or structural properties of the outer layers of the exoskeleton. Most beetles are black as a result of melanin deposition during sclerotization, the chemical hardening process of the exoskeleton that occurs after emergence from the pupa, or eclosion. Microscopic surface sculpturing also influences beetle colors, as do patterns of setae, scales, or waxy secretions. Black desert darkling beetles (Tenebrionidae) are sometimes partially or completely covered with a white, yellow, or bluish-gray waxy bloom that reflects light and helps to keep the beetle cool.
The brilliant iridescent and metallic colors of beetles are created by multiple reflective layers in the exoskelton and scales, or a layer of highly complex photonic crystals that reflect light at different wavelengths to create specific metallic colors and shimmering iridescence. These structures are determined genetically, but their final form in individual beetles is determined by conditions experienced during growth and development.
As with other insects, the beetle body is divided into three distinct regions: head, thorax, and abdomen.
The hardened head capsule is attached to the thorax by a flexible and membranous neck, and is clearly visible from above or partially withdrawn inside the thorax. It bears chewing mouthparts that typically consist of an upper lip (labrum), two sets of jaws (mandibles, maxillae), and a lower lip (labium). The usually conspicuous mandibles are modified to cut, grind, or strain various foodstuffs. The maxilla and labium may possess delicate fingerlike structures, or palps, that help manipulate food. Beetle mouthparts are directed forward, or prognathous (e.g., whirligig beetles [Gyrinidae], ground beetles [Carabidae]), or downward (hypognathous), as in leaf beetles (Chrysomelidae) and weevils. The mouthparts of some beetles, especially those of weevils (Curculionoidea), are borne at the very tip of a snout-like rostrum, an adaptation often associated with flower- or seed-feeding habits.
Although usually shorter than the body, the antennae are much longer in many longhorns (Cerambycidae) and brentid weevils (Brentidae). Equipped with incredibly sensitive receptors, these appendages help beetles detect food, locate egg-laying sites, identify vibrations, and assess temperature and humidity. Those of males are sometimes quite elaborate and are packed with chemical receptors for detecting pheromones, sexually attractant odors released by females. Each antennal segment is referred to as an antennomere. The basic number of antennomeres for beetles is 11, but reductions to as few as seven are common, while 12 or more occur in some species. Antennal modifications are described as filiform (threadlike), moniliform (bead-like), serrate (saw-toothed), pectinate (comb-like), flabellate (feather-like), clavate (gradually clubbed at the tip), capitate (abruptly clubbed at tip), lamellate (terminal antennomeres flattened or plate-like), or geniculate (elbowed).
The compound eyes are entire (rounded or oval in shape), emarginate (kidney-shaped), or are completely divided, as in the whirligigs (Gyrinidae). They are often reduced in flightless species, or absent altogether in cave and litter species that dwell in total darkness. Ocelli, simple eyes limited to detecting light and dark, are found only in a few rove beetles (Staphylinidae), some leiodids (Leiodidae) and derodontids (Derodontidae), and in most hide beetles (Dermestidae).
Male heads are sometimes adorned with extraordinary antler- or tusk-like horns that may vary greatly in size depending on overall body size, larval nutrition, and other environmental and genetic factors. Horns enhance the reproductive capabilities of males and are used in battles against rival males to butt, block, pry, or lift them out of the way.
The beetle thorax consists of three segments, each bearing a pair of legs. The clearly visible midsection of a beetle is the prothorax, the upper or dorsal surface of which is covered by a plate, the pronotum. The pronotum may bear horns that work in concert with those of the head, or is scooped out to facilitate burrowing in the soil or rotten wood. The mesothorax and metathorax bear the elytra and membranous flight wings, respectively. They are broadly connected to one another and are hidden under the elytra. The ventral sclerotized plates for these two thoracic segments are termed the meso- and metaventrite. Dorsally, the elytra usually meet along a straight line down the back called the elytral suture. A small triangular plate of the mesothorax called the scutellum is often visible between the bases of the elytra.
The legs are modified for burrowing, swimming, crawling, running, or jumping, and usually consists of six distinct segments. The coxa is generally short and stout, and firmly anchors the leg into the coxal cavity of the thorax, yet allows for the horizontal to-and-fro movement of the legs. The trochanter is usually small and freely movable in relation to the coxa, but fixed to the femur. The femur is the largest and most powerful leg segment and is greatly enlarged in species that jump (e.g., Scirtidae). The tibia is usually long and slender, but may be modified into a rakelike structure on the front legs of burrowing species, or fringed with long setae to enhance their use as oars by aquatic beetles. The tarsus is typically divided into multiple articles called tarsomeres, and ends in a claw-bearing segment referred to as the pretarsus. Each tarsus consists of up to five tarsomeres (including the pretarsus), the exact number of which may be of diagnostic value and is expressed as a three-digit tarsal formula (e.g., 5-5-5 or 3-3-3), which indicates the number of tarsomeres on the front, middle, and hind legs, respectively. The penultimate tarsomere is often difficult to see without examination under high magnification, a fact denoted by the statement "appears 4-4-4, but actually 5-5-5."
Beetles typically have five visible abdominal segments, although there can be up to eight. Each segment is comprised of four plates, or sclerites: a dorsal tergum or tergite, the ventral sternum, and two lateral pleura. The dorsal terga are thin and flexible in beetles with abdomens completely covered by the elytra, but are thicker and more rigid in rove beetles (Staphylinidae), clown beetles (Histeridae), and others with short elytra. The penultimate and ultimate terga are called the propygidium and pygidium, respectively. The lateral pleura are usually small, more or less hidden from view, and have a single breathing pore, or spiracle. The ventrally visible abdominal sterna are called ventrites. Ventrites are numbered beginning at the base of the abdomen and are separated by deep to shallow transversal divisions called sutures, or by narrow membranes. The internal copulatory organs of males are often of great value in species delimitation and identification.CHAPTER 2
Our efforts to classify and understand the evolutionary basis for the diversity of beetles and other organisms are called systematics. Systematic study involves two narrowly defined, yet highly interdependent fields—taxonomy and phylogenetics. Taxonomy is the science and practice of recognizing, describing, and naming species, while phylogeny is the study of the relationships of taxa based on their shared evolutionary history to develop a natural, rather than artificial, classification. Overall, beetle species and their genera are currently placed in 1,663 tribes, within 541 subfamilies, nested in 211 families grouped into four suborders (see here).
A beetle species is the smallest aggregation of populations that is distinguishable by a unique set of characteristic traits resulting from reproductive and, therefore, genetic isolation. Some species are easily diagnosed on the basis of genital configuration, while others may require the examination of many individuals from different populations to discern traits that are consistently different among closely related species.
Linnaeus initiated the naming of organisms using only two words, the genus and species, or binominal name (commonly called the scientific name). The binominal is usually italicized and the genus is always capitalized. In scientific documents, the scientific names of beetles are generally followed by the surname of the person who first described the species and the year in which it was described. When a species originally described in one genus is transferred to another subsequently, parentheses are placed around the author's name and year of description. The year of publication of a name establishes its nomenclatural priority in the event that someone else comes along later and mistakenly describes the same species again under a completely new species name (a synonym), or inadvertently uses the same name to describe a totally different species (a homonym).
The formation and use of scientific names are codified in the International Code of Zoological Nomenclature. When describing a new species of beetle, a coleopterist designates one of the specimens used for the description as the holotype. The holotype, placed in the care of a museum or other public institution where it will be accessible to other researchers for examination, will for ever serve as the name bearer and international standard for that species. Beetle species are typically grouped into genera, subtribes, tribes, subfamilies, families, superfamilies, and suborders, although in some cases (in the less diverse groups) not all ranks are used. Some ranks end in universally accepted suffixes, such as subtribes (-ina), tribes (-ini), subfamilies (-inae), families (-idae), and superfamilies (-oidea).CHAPTER 3
EVOLUTION & DIVERSITY
The remains of the ancient beetle-like Protocoleoptera and true beetles are abundant in the fossil record, mostly as impressions in sedimentary rock or entombed in petrified tree sap called amber. Fossil Protocoleoptera are known from the Lower Permian rocks of eastern Europe, dating back about 280 million years. The insects were flattened, probably occupied tight spaces under loose bark, resembled the modern insect order of Megaloptera (alderflies, dobsonflies, and fishflies), and likely included precursors to several modern holometabolous insect orders. Protocoleopteran elytra had distinct ribbing and sculpturing resembling that of species in the extant family Cupedidae, but were less regularly sculptured and extended beyond the abdomen. Modern Coleoptera replaced the protocoleopterans by the Late Triassic (240–220 million years ago), when all four of today's beetle suborders were present. Based on fossil evidence from Europe and Central Asia, the evolutionarylineages of all of the modern Coleoptera were established by the Jurassic (210–145 million years ago).
Amber secreted by conifers during the Jurassic suggests that these ancient trees were already under attack by wood-boring insects similar to modern bark beetles (Curculionidae). At least 60 beetle families have been found preserved in amber, most of which are attributable to tribes and genera that still occur to this day. Amber deposits with fossil intrusions formed in tropical forests and other ancient habitats are poorly represented in the fossil record.
Most fossil beetles from the Quaternary period (1.6–0.5 million years ago) are identical to modern beetles. Their remains are not fossilized, but instead were preserved among permanently frozen detritus, water-lain sediments, prehistoric dung middens, or asphalt seeps.
Mostly small and compact, beetles are well equipped to exploit most terrestrial and freshwater habitats. Beetles owe much of their success to the possession of elytra, allowing the effective concealment of soft membranes that are exposed in other insect groups. Whether beetles live on land or in the water, their elytra protect them from abrasion, desiccation, parasites, and predators. Between the elytra and abdomen is the subelytral cavity, an important adaptive feature used by both terrestrial and aquatic beetles. For example, desert species use the subelytral space to insulate the body from sudden changes in temperature and to prevent desiccation, while some aquatic beetles use this space to capture and store oxygen in order to breathe under water. The ability of many beetles to fly also increases their chances to avoid predators, find food, locate mates, and colonize new microhabitats.CHAPTER 4
COMMUNICATION, REPRODUCTION & DEVELOPMENT
Beetles communicate with each other using lights, smells, or sounds. Many fireflies (Lampyridae) are bioluminescent and attract mates by producing their own lights, with males and females exchanging species-specific flash patterns. The females of many species emit chemical odors, or pheromones, that sexually stimulate conspecific males. Beetles also increase their chances of finding a mate by gathering around odiferous food sources, especially carrion, dung, flowers, or sap flows. Some scarabs (Scarabaeidae), longhorn beetles (Cerambycidae), and bark beetles (Curculionidae), produce sounds by stridulation, or rubbing parts of their bodies together. Male deathwatch beetles (Ptinidae) bang their heads against the walls of their wooden galleries to attract the attention of females, while southern African darkling beetles known as tok-tokkies (Psammodes) drum their abdomens against rocks and soil to attract mates.
Elaborate courtship behaviors immediately prior to copulation are uncommon among beetles, although the males of some species (e.g., in families Cantharidae, Meloidae, and Cerambycidae) do briefly engage in licking and touching behaviors using their mouthparts, antennae, legs, and genitalia before copulation. In most species, the male simply mounts the female briefly and may remain in contact with her afterward to block the advances of other males and assure his paternity. Females store the male's sperm in a special pouch, or spermatheca, until fertilization occurs as the eggs are being laid.
DEVELOPMENT AND PARENTAL CARE
Eggs are carefully buried singly or in batches in the soil, or placed in or near the appropriate larval foodstuff. Upon hatching, the larva's mission is simple—to eat and grow. Larvae that scavenge carrion and dung or mine plant tissues tend to be grub- or worm-like, while predatory species are generally flattened and leggy. Predatory larvae typically feed on other arthropods, although some prey on small vertebrates. Species with larvae that areparasitoids (parasites that eventually kill their host) of other insects (e.g., members of Ripiceridae and Rhipiphoridae) develop by hypermetamorphosis, where the first larval instar is active and leggy, while the remaining instars are grub-like and relatively inactive.
Excerpted from The Book of Beetles by Patrice Bouchard. Copyright © 2014 Ivy Press Limited. Excerpted by permission of The University of Chicago Press.
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