Coleoptera Families 2
Dermestidae: skin and carpet beetles
Biology and Behavior: Skin beetles (many also known as carpet beetles) are a relatively small group of common beetles, with about 700 species worldwide. As larvae most scavenge dried materials, especially those rich in protein. Many feed on dead insects or dried plant materials. They are also often found associated with late-stage, decaying carcasses that are somewhat dried. There they feed on most remaining tissues except bone. Some skin beetle larvae are associated with various nests, where they feed on dead individuals and food stores (bee and wasp nests), feathers (bird nests), or fur (mammal nests). Some are associated with the egg cases of praying mantises or spiders, while a few species are predators of the larvae and eggs of bees and wasps (and eggs of spiders). Lastly, some can be found feeding on grains and cereals. Adults are sometimes found at flowers where they feed on nectar and pollen. Like many flies, some skin beetles pupate within the last shed larval skin. The odd beetle (Thylodrias contractus[1]) is strange among other Dermestidae in that males are elongate with long legs and antennae, and have soft elytra; females are equally strange, lacking wings and resembling larvae.
Economic Importance: Skin beetles are known to be both pests and beneficials. Most of their pest status has to do with the tendency of larvae to feed on things we value. Carpet beetles (Anthrenus spp.) and others that live in our homes may feed on animal products including wool fabrics and carpets, furs, leather, and silk. They may even feed on other materials such as linens, cotton, rayon, etc., especially when these items are soiled. Other Dermestidae are know to feed on our stored grains and products, such as rice, oats, beans, corn, and others. Of these the khapra beetle (Trogoderma granarium) is probably to most widespread and important. Skin beetles can also be extremely damaging to insects specimens in collections, and taxidermied animals in personal collections or museums. In certain museum situations, however, skin beetles (especially larder beetles, Dermestes spp.) are extremely useful for cleaning the bones of animals that are meant to be displayed as skeletons. In this same respect Dermestidae are important for helping to dispose of the last bits of carcasses in nature, and thus are considered beneficial decomposers. Another aspect of this is that they are sometimes used in forensics to determine the time of death in human legal cases. Lastly, some adult Dermestidae that visit flowers can be considered pollinators.
How to identify Dermestidae: Skin and carpet beetles are small to medium-sized beetles ranging in size from 1-12 mm in length. They are generally oval to spherical and fairly thick/convex (hump-backed) with a head that is often hidden under the pronotum (somewhat like Anobiidae). Most are dull and have either many hairs/setae covering the body or small scales. In Anthrenus and other genera the scales may form patterns of white, gray or even red/yellow/orange. Most species have short, clubbed antennae that fit in grooves when contracted; the antennal club can vary in number of segments and shape. Unlike most beetle families, many skin beetles have a simple eye (ocellus) on the center of their head [2]. The legs of skin beetles are usually retractable, especially the hind ones where the femora fit into a groove in the coxae. All legs have 5 tarsal segments, with the first four being shorter than the last segment. Dermestid larvae are elongate and generally tear-drop shaped with a well-developed head and legs. Most have body segments that are ring-like and separated by tufts of setae (sometimes with large tufts at the end of the body), giving them a pipe-cleaner look.
Links & References:
Skin and carpet beetles on Bugguide
Fabric pests including carpet beetles
Video of skin beetles being used to clean trophy skeletons
Common Carpet Beetle Anthrenus scrophulariae
Bostrichidae: horned powder-post beetles
Biology and Behavior: Horned powder-post beetles (including the traditional powder-post beetles, formerly in the family Lyctidae [3]) are a small family of beetles with about 550 species worldwide. All larvae are associated with plant materials, most commonly the wood of dead trees. Members often create small, pin-hole tunnels in the wood of twigs, branches or trunks. These wood-feeding types utilize microorganisms in their gut to help digest the tough cellulose and also have an efficient system for retaining water while feeding on extremely dry materials. Some attack stored products, while others feed on living plant tissue or fungus.
Economic Importance: Powder-post beetles that attack wood can become pests of lumber and wooden structures. Their feeding creates many small holes in the wood, affecting its integrity and aesthetics. The few that attack living plants may harm their growth, though the most important of these is probably the giant palm borer (Dinapate wrightii [4]) which is native to the southwestern US. They are the largest Bostrichidae at 60mm and attack weakened California fan palms and date palms. A few species, such as the lesser grain borer (Rhyzopertha dominica [5]) and the larger grain borer (Prostephanus punctatus [6]), attack dried seeds and grain stores. They are common across the world and can infest commercial and household areas. Lastly, one amazing species, the lead cable borer or short circuit beetle (Scobicia declivis), is able to bore through soft metals (lead), shingles and wires where it may damage or short-out electrical systems; normally this species attacks trees.
How to identify Bostrichidae: Bostrichidae range in size from small to large, being 1.5 to over 60mm long (most 2-20mm). They are generally elongate and cylindrical, much like pills. Most have a bulging, spiny pronotum (sometimes with horns) with a downward-facing head positioned underneath (right). They also often have blunt or abruptly-ending elytra, often also with spines. They are sometimes confused with bark beetles (Curculionidae: Scolytinae) in general appearance. Members of Lyctinae and a few other groups have a more flat appearance, with a normal pronotum, abdomen, and forward-facing head. Some are colorful, but most are rough with various shades/mixes of brown or black. Powder-post beetles have normal to enlarged eyes and straight antennae with a two to four-segmented club (sometimes with club segments finger-like). They may have moderate to large mandibles. All have normal legs, usually with a 5-5-5 tarsal formula (some like Psoa are 4-4-4 [7]); the first tarsal segment is often the smallest. Larval Bostrichidae are c-shaped grubs much like Scarabaeidae and Anobiidae [8]. They often have an enlarged head and thorax region, with a tapering abdomen.
Links & References:
Horned powder-post beetles on Bugguide
Silvanidae: silvanid flat bark beetles
Biology and Behavior: Silvanids ("flat bark beetles" once considered part of the family Cucujidae) represent a small family (~500 known species) of beetles that are usually secretive. They are often found under the bark of dead trees, where most feed on fungus (sometimes being predators). A few venture out onto leaves and the open ground, while some are associated with ants. The most well known are species that attack grains and stored products. Very little is known about the biology of many silvanid species.
Economic Importance: A few species of silvanids are pests of our stored foods, feeding as larvae and adults. Products affected include grains, rice, nuts, flour, bread products, dried fruits and other similar products. A few genera contain species known to infest such commodities, but the most common and important species are the sawtooth grain beetle (Oryzaephilus surinamensis) and the merchant grain beetle (Oryzaephilus mercator) [9]. Though the latter does not fly much, both beetles are transported readily in stored commodities and are common throughout the world.
How to identify Silvanidae: Silvanid flat bark beetles are small to minute (2-15mm) and, as their name suggests, are usually somewhat to greatly flattened. They are generally rough, sometimes hairy, and a uniform brown to reddish-brown or tan (right). Silvanids usually have a narrow waist (connection between the pronotum and elytra) and a triangular head. The eyes are located on the sides of the head and have a distinct neck-like constriction behind them, a good diagnostic character for the family. Their antennae are either long and filiform (with an elongate first segment) or shorter with a small, three-segmented club. Silvanids have a 5-5-5 tarsal formula, with the shape and length of the segments being variable. Larvae are variable, but generally elongate, parallel-sided, and pale, with a somewhat flattened head.
Links & References:
Nitidulidae: sap beetles
Biology and Behavior: Sap beetles are a fairly-common family of about 2,800 species worldwide. Most, as alluded to by the name, are saprophaghous meaning they feed on rotting materials. This can include rotting vegetable matter, over-ripe fruits, and other fermenting materials (including carrion). They even feed on sap flows from wounded trees. Many are associated with fungi, while some live in the nests of other insects, feeding on fungus growing inside or on their products/stores. Lastly, some species are predators of other insects.
Economic Importance: Most sap beetles are benign, but some are known to be pests. The most important pest is the small hive beetle (Aethina tumida [10]), which is originally from South Africa and damages commercial honey bee hives. Larvae burrow through the wax and feed on the honey, defecating and causing a loss of honey and rotting/fermentation throughout [11]. Small hive beetles are able to destroy entire hives, causing bees to abscond to a different site. Sap beetles are also known to sometimes transmit oak wilt to trees [12], by being attracted to and feeding on the fungus and transferring spores to living tree wounds when they are feeding on sap. A few species are pests of ripe fruit (including corn) or stored grains. Despite some pests there also beneficial sap beetles, especially those whose larvae hunt pests like bark beetles (Curculionidae: Scolytinae) and scale insects (Hemiptera: Coccoidea).
How to identify Nitidulidae: Sap beetles are a fairly distinct family of minute to small (1.5-12mm) insects. Most are brown, black or mottled, but some like Glischrochilus [13] are shiny black with red/orange/yellow spots. Most are flattened to slightly flattened and oval in shape, and may have texture or hairs. Sap beetles usually also have a strong head and jaws. The most recognizable feature is their shortened elytra, which show from the tip of the abdomen to as many as three abdominal segments. Other characteristics of the family include: 11-segmented antennae ending in a three-segmented club; 5-5-5 or 4-4-4 tarsal formula with tarsal segments usually being lobed except for a short fourth segment and an elongate last segment; legs that may be flattened or retractable against the body. Larvae [14] of sap beetles are variable, but usually elongate with three pairs of legs and various plates or spines along the body.
Links & References:
Coccinellidae: lady beetles and relatives
Biology and Behavior: Ladybugs or lady beetles, and bean/squash beetles comprise a group of almost 6,000 species worldwide. The majority of ladybugs feed on soft-bodied insects as larvae and adults. Prey may include scale insects, mealybugs, aphids, whiteflies and mites. A few species feed on pollen, while one group (Epilachninae [15]) feeds on living plant tissue. Rarely larvae are found in ant or termite nests. Many ladybugs are brightly-colored to warn that they are distasteful or toxic. In fact many are known to exhibit reflexive bleeding, where they exude sticky, noxious liquids from their leg joints to deter predators. Ladybugs may form large masses made up of hundreds to thousands of individuals when overwintering or dormant in warm weather. They sometimes even migrate to locations to do so (including human structures).
Economic Importance: Many ladybugs are important control agents of plant-feeding insects, particularly pests such as sucking bugs (Hemiptera: Sternorrhyncha) and certain mites. Adults and larvae are voracious and can decimate populations of these pests. For this reason they are sometimes imported from other parts of the world for biocontrol of invasive insects, and the most famous example is the vedalia beetle (Rodolia cardinalis [16]) which was imported from Australia to control the cottony-cushion scale (Icerya purchasi) in California. Some ladybugs, however, are pests themselves by directly feeding on crops. In the US two species are known to exhibit this lifestyle: the squash beetle (Epilachna borealis) and the Mexican bean beetle (Epilachna varivestis). The latter attacks beans and other legumes, while the former is a pest of squash and related commodities. Lastly, some ladybugs like the multicolored Asian lady beetle (Harmonia axyridis [17]), were imported for biocontrol of pests but end up becoming pests themselves, displacing native ladybugs and becoming a nuisance to homeowners when they infest houses (even being known to stain materials, smell badly, cause allergies and, in extreme cases, bite).
How to identify Coccinellidae: Ladybugs generally range in size from 0.8-11mm. Many ladybugs are familiar to people, being the stereotypical shiny red with black spots (usually with a black and white pronotum; right). However their diversity is immense and not all have that characteristic coloration: they can be black (sometimes with red spots), gray, yellow, orange, pink, splotched, striped or without patterns [18]. A few are metallic blue, green, or purple. Many are shiny, or slightly dull, while others are rough and even hairy in appearance. All are either spherical or sub-spherical in shape, and usually convex above and flattened on the bottom. Specific characteristics include clubbed antennae and an apparent 3-3-3 tarsal formula (in most, truly 4-4-4 with a small third tarsal segment). Ladybug larvae are often black or brown with orange/red markings and resemble fast-moving, long-legged caterpillars (left). Some, however, are covered in spiny projections (left) or coated in white wax and resemble mealybugs, their prey of choice [19].
Links & References:
Other beetle pages:
Coleoptera: Introduction
Coleoptera Families 1: scarabs, jewel beetles, click beetles, and relatives
Coleoptera Families 3: leaf beetles, longhorn beetles, weevils, and relatives
