(Reprinted from Y.E.S. Quarterly 11(2), APR/JUN 1994)

by Gary A. Dunn and Daniel K. Young

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The insect order Coleoptera is the largest order in the entire animal kingdom and contains about 40% of all insects. Conservative estimates place the number of species at around 400,000, but recent investigations in the Amazon region of South America are suggesting the actual number could be closer to 2.5 million species! Some of the families within this order contain several thousand species each.

The habits of beetles are highly variable. Some live in the soil or decaying animal or plant matter (dung, carrion, refuse, rotting wood, humus, etc.). Many live on or in plants; others live in aquatic and semiaquatic situations. Beetles may be predators, parasites, plant feeders, and/or scavengers. The beetles have been a tremendously successful group because of their ability to adapt, both as larvae and adults, to many habitats (including many highly specialized microhabitats within macrohabitats).

As a result, beetles have evolved into a seemingly endless array of body sizes, body shapes, and colors. this incredible variation is often the basis for difficulties encountered when first trying to learn beetle identification. There are approximately 120 families of beetles which occur in the continental United States and Canada. Of this number, some two dozen families contain the majority of the species and account for 80% of the beetles commonly seen in North America.

The identification of Coleoptera to even the family level is sometimes difficult. Often the characters used to differentiate between some families are difficult to see or interpret. Fortunately you can learn to recognize most of the common beetle families through a combination of "general appearance" features such as size, shape, coloration, antennal structure, and/or tarsal structure. Some families, even those with thousands of species, have a single definitive character that immediately separates it from all other families (like the snout of the Curculionidae (weevils). Eventually, however, you will develop a "feel" for even some of the more difficult families. The ability to make accurate, speedy identifications takes time and experience, so don't give up!

The secret to beetle identification is to learn the conspicuous features that are associated with each particular family. You must learn to distinguish between "trivial" characters, those which only belong to a single genus or species, and the diagnostic characters that apply to all or most all of the genera and species in the family.

Common Beetle Families

1. CICINDELIDAE (tiger beetles)

The tiger beetles are brightly colored beetles that frequently have a metallic luster. The head is quite large and is wider than the pronotum of the thorax. The legs are long and slender and provide these beetles with the ability to run very rapidly; they are also quick to take flight when approached or pursued. Both the adults and larvae are predaceous. The adults of the largest genus (Cicindela) are diurnal and are most frequently found in open areas with sparse vegetation. The adults of the other North American genera (Megacephala, Omus, and Amblychila) are nocturnal. The larvae of all genera live in burrows and capture other small insects as they walk by.

2. CARABIDAE (ground beetles)

The members of this beetle family exhibit a great deal of variation in size and shape. Many species are darkly colored, sometimes shiny or even metallic, and somewhat elongate and flattened. In contrast to the closely-related tiger beetles, the heads of most ground beetles are narrower than the pronotum of the thorax.

The majority of these beetles are predaceous, but a significant number of species (even whole genera) are scavengers or seed feeders. Most ground beetles are active primarily at night and are commonly seen at lights.

3. DYTISCIDAE (predaceous diving beetles)

The predaceous diving beetles possess a smooth, oval body with flattened hind legs. The hind legs are generally fitted with a fringe of hairs to aid in swimming. The outer margin of the pronotum is often marked with light brown or yellow, and some members of this family have the elytra (wing covers) sculptured with longitudinal grooves.

As the common name implies, these beetles feed on other insects and small invertebrates. The larvae are also predaceous, and are commonly called "water tigers". Both the adults and larvae are aquatic, but the nocturnally active adults are often seen at lights.

4. GYRINIDAE (whirlygig beetles)

Whirlygigs are black in color and oval to elliptical in shape. Each compound eye is divided into an upper and lower half, giving the appearance of two pairs of eyes. The middle and hind legs are short (not seen from above) and greatly flattened for swimming.

The unusual name for these beetles refers to the way in which they swim: in circular patterns on the surface of ponds, lakes and quiet streams. the adults and larvae are predaceous.

5. HYDROPHILIDAE (water scavenger beetles)

The water scavenger beetles look similar in appearance to the predaceous diving beetles, but unlike the dytiscids most water scavenger beetles possess a long spine (or "keel") on the underside along the midline and are unicolorous shiny black.

Most of the water scavenger beetles are indeed aquatic, but some species are terrestrial and live in damp soil or animal manure. While some species are largely scavengers, at least a few species are predators. Some members of this family are attracted to lights at night.

6. SILPHIDAE (carrion, sexton, and burying beetles)

The silphid beetles are soft-bodied and more-or-less flattened. the wing covers are generally widest at the tip (giving a wedge-shapped appearance to the body) and generally marked with irregular crossbands of yellow, orange, or red. These beetles have clubbed antennae, and the broad, spiny legs are adapted for digging.

As the common names imply, these beetles are scavengers associated with animal carcasses. However, a few species are associated with decay fungi and some are predaceous.

7. STAPHYLINIDAE (rove beetles)

The rove beetle family is a large one, but most all of the species can be recognized by the long, slender body and the shortened elytra (wing covers) which leave the majority of the abdomen visible from above. The hind wings are folded up underneath the elytra when not in use and are therefore not visible even though they are actually much larger than the front wings.

The adults and larvae of this family are mostly predaceous, and occur in and around dead organic matter (plant and animal), under rocks and logs, near margins of lakes and streams, and in a variety of other terrestrial habitats. Some even live in the nests of other insects, such as termites and ants. Many are active at night and many are attracted to lights.

8. LUCANIDAE (stag beetles)

The stag beetles are mostly medium to large-sized beetles that are usually brownish or blackish in color. They are closely related to the scarab beetles, but differ in having the antennae elbowed with terminal segments that are not capable of being held tightly together.

These beetles are named for the large, antler-like mandibles that the males of many species possess. They occur primarily in wooded areas where the larvae feed on decaying wood. Adults are often attracted to lights.

9. PASSALIDAE (bess beetles/horned passalus beetles)

This family is largely tropical in distribution, so throughout the eastern part of the United States there is but one representative of this species: Popilius disjunctus (Illiger). This beetle is rather large, elongate, and shining brownish or blackish. Furthermore, there is a single prominent "saddlehorn" on the front of the head in the middle. they are found in decaying logs in which they form communal galleries. When handled they frequently make a squeaking noise which is produced by rubbing the wings against the abdomen.

10. SCARABAEIDAE (scarab, flower, and dung beetles)

This is a very large and diverse family with both large and small members. Some of our largest modern-day beetles belong to this family. Virtually all members of this family can be identified by the unusual clubbed antennae. The last 3-5 segments are enlarged to form an asymmetrical club which is capable of being moved (much like moving the fingers of your hand together or apart).

There are two major types of scarab beetles: those that feed on plants (flower beetles, junebugs, or chafers) and those that feed on dung or animal carcasses (dung beetles and skin beetles). A few of the scarabs live in the nests of ants or termites. Many scarabs are nocturnal and can be found at lights.

11. LAMPYRIDAE (lightningbugs or fireflies)

Many fireflies are able to produce light from the undersides of their abdomens. The light produced is usually yellowish-green; the underside of the abdomen near the tip is also this color when viewed in daylight. Not all fireflies produce light, and so some look very similar to soldier beetles. However, the lampyrids differ in having most of the head concealed by the pronotum (and appearing retracted).

The larvae of these beetles are predaceous, usually on snails and other soft-bodied animals, and the adults are primarily plant feeders.

12. CANTHARIDAE (soldier beetles)

The soldier beetles are elongate, soft-bodied beetles, similar in appearance to some lampyrids. They differ from the fireflies in that the head protrudes out in front of the pronotum and is not concealed from above. In addition, no members of the soldier beetles are able to "glow".

The adults are common on flowers and foliage; members of the genus Chauliognathusare yellow and black and are very common on the flowers of goldenrod.

13. DERMESTIDAE (carpet and hide beetles)

Members of this beetle family are usually small, oval or elongate-oval, tightly compact beetles with short, clubbed antennae. The legs and antennae are frequently difficult to see, especially in dead specimens, because they are tightly pressed to the body and fit into shallow grooves. Many of these beetles are covered with hairs or short, flattened scales of various colors.

The larvae and adults of the dermestid beetles are generally associated with protein-rich food sources such as animal hides, hair, organic fabrics, pollen, human and pet foods. They may also become serious pests in unprotected insect collections!

14. ELATERIDAE (click beetles)

Click beetles range in size from very small to large, and are commonly rather elongate with a large pronotum that is produced along the posterior angles into spine-like processes. Click beetles are generally drably colored, but a few have contrasting markings and some are metallic. The most interesting feature for members of this family is their ability to "click". The clicking mechanism occurs on the underside and is composed of a spine that extends posteriorly from the prosternum and fits into a groove in the mesosternum. With this mechanism the click beetles can flip themselves in the air, often with an audible "clicking" sound; it helps them to turn themselves over when they are on their backs, and probably is of use in avoiding predators.

The larvae are hard-bodied, elongate forms commonly referred to as wireworms. Many are phytophagous (sometimes reaching pest status), but some are predaceous. Adults occur on foliage, or logs and stumps. Many are also attracted to lights at night.

15. BUPRESTIDAE (metallic wood boring beetles)

The metallic wood boring beetles are closely related to the click beetles, and this accounts for the similarity in body shape. (They differ in lacking the clicking mechanism and the hind angles of the pronotum are not produced.) Most are bright metallic in color (especially on the underside).

Metallic wood boring beetles are phytophagous and are usually found in association with recently killed trees. As a rule the adults are most active on bright, sunny days. Under such conditions they frequently occur in large numbers on log piles and stumps where they mate and lay eggs. A few seem to be attracted to heat and can be seen running over still smoldering timbers after a forest fire. The larvae, called flat-headed borers, tunnel into wood where they generally require one to several years to develop into adults. A few of the metallic wood boring beetles are leaf miners, and a couple are responsible for gall formation.

16. MELOIDAE (blister beetle)

The blister beetles are soft-bodied and have a small pronotum that is narrower than both the head and elytra. They may be striped or unicolorous (one common species is black and can be found on goldenrod flowers in the late summer). The common name refers to their ability to produce a substance called cantharidin, which can cause irritation and blistering of the skin in humans. The cantharidin secretion is used by these beetles as a defensive mechanism.

The larvae are parasitic (primarily on grasshoppers) and the adults feed on foliage and flowers.

17. TENEBRIONIDAE (darkling beetles)

This family is especially prominent in the southwestern United States, and its members are extremely variable in appearance. For the most part adult darkling beetles are darkly colored. Two characteristics that can help you recognize members of this family include the 5-5-4 tarsal formula (where the number represent the number of tarsal segments on each of the three pairs of legs; notice the last pair of legs has a reduced number of segments) and the eyes which are "notched" or "bean-shaped" (emarginate) along the front margin.

In the arid regions, darkling beetles can be seen wandering across the ground (both day and night); in the eastern portion of the country they are often associated with dead trees, shelf fungi, and sandy areas. Several of the smaller species are significant pests of stored grain products.

18. COCCINELLIDAE (ladybird beetles)

The ladybird beetles are small to medium-sized, oval beetles that are usually brightly colored (red or orange with black spots, or the reverse). Some members of this family can be confused with the leaf beetles, but ladybird beetles have distinct clubbed antennae and a different tarsal formula.

Both the larvae and adults are predaceous and are of great benefit to humans by devouring large numbers of aphids, mealybugs, and scale insects. However, members of the genus Epilachna (bean beetles) are phytophagous and can cause substantial damage.

19. CHRYSOMELIDAE (leaf beetles)

The leaf beetle family is a large one, with many common species. Many are similar in appearance to the ladybird beetles, but others are more elongate. The antennae are threadlike (filiform) and generally less than half the length of the body. Many of the leaf beetles are striped or patterned, and some resemble tiny tortoises in shape.

The majority of the species are phytophagous as both larvae and adults; many are serious plant and crop pests (for example, cereal leaf beetle, corn rootworms, Colorado potato beetle, asparagus beetle, locust leafminer, etc.).

20. CERAMBYCIDAE (long-horned beetles)

The long-horned beetles usually have rather long antennae, commonly longer than the length of the body. The eyes are "notched" or "bean-shaped" (emarginate) and the antennae arise in or near this notch. The next-to-last tarsal segment is also "notched" or "split" (bilobed), and the last tarsal segment is attached between the lobes. Most of these beetles are elongate and narrow-bodied, and may be unicolorous or striped.

The larvae, commonly referred to as round headed borers, create tunnels in wood. The adults are generally found on trees, logs and stumps, on flowers, and at lights.

21. CURCULIONIDAE (snout beetles or weevils)

The weevils can be easily recognized by their elongate snout. In a few species the snout is broad and not as obvious, so look for the elbowed antennae (which are often clubbed at the tip). This is the largest family of beetles, and as such, exhibit tremendous diversity in size, shape, and color. Many are compact and hard-bodied, but others are more elongate and soft-bodied. Some are covered with scales.

Most weevils are found in association with plants, as wood borers, leaf miners, gall makers, and foliage feeders. Some also feed on seeds, fruits, and roots. Many are attracted to lights at night.

USEFUL REFERENCES

Arnett, R.H. and N.M. Downie. 1980. How to Know the Beetles. W.C. Brown Co. Dubuque, IA. 416pp.

Dillon, E.S. and L.S. Dillon. 1961. A Manual of the Common Beetles of Eastern North America. Dover Publications. Mineola, NY. 884pp.

Dunn, G.A. 1994. The Insect Identification Guide (4th Edition). Young Entomologists' Society. Lansing, MI. 70pp.

Papp, C. S. 1984. Introduction to North American Beetles. Entomography Publications. Sacramento, CA. 333pp.

White, R.E. 1983. A Field Guide to the Beetles of North America. Houghton Mifflin. Boston. 496pp.

Zahradnick, J. 1985. Kafer Mittel und Nordwesteuropas. Paul Parey Publications. Berlin. 497pp (in German)

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