The Structures of Life Module is Growing...with Bess Beetles

FOSS Newsletter Staff
March 03, 2003 | Program News

The FOSS Structures of Life Module for grades 3–4 ©2000 consists of four sequential investigations dealing with the observable characteristics of organisms. Students observe, compare, categorize, and care for a selection of organisms including plants, crayfish, and land snails. Students investigate structures of the organisms and learn how some of the structures function in growth and survival. The module will soon grow to include a fifth investigation called Meet the Bess Beetle. Here's a sneak preview of the new addition to the FOSS family of organisms.

Why a New Investigation?

This fifth investigation is being developed especially for teachers and students in states where the land snail, Helix aspersa, is considered a pest and is not allowed in the state. We selected the bess beetle as an alternative organism to the land snail because it fits the FOSS criteria. For an organism to be considered for FOSS, it must be safe for students to handle, easy to care for, able to survive well in classroom environments, large enough for students to make detailed observations, and exhibit structures or behaviors of interest to students. Studying the organism must provide opportunities for student concept development in life science. It is a bonus when the organism is native or naturalized in the region so students might find them in the local environment. While the land snail, Helix aspersa, is still recommended for those states where the organism is already naturalized, we recommend use of the bess beetle—formally known as Odontotaenius disjunctus—for other states.

Closeup of a Bess Beetle

Introduction to Beetles

Insects make up about 60 percent of the known animals. At least a third of those insects are in the order Coleoptera, the beetles, including some 350,000 different beetle species. One out of every five animal species known on Earth is a beetle. Lady bird beetles, fireflies, whirligig beetles, and darkling beetles (the mealworm adult stage) are all in this order. Like other insects, beetles wear their skeletons on the outsides of their bodies instead of inside like people. This outside skeleton is called an exoskeleton. All insects have three pairs of legs. Their bodies are divided into three parts—head, thorax, and abdomen. Most insects have two pairs of wings, and their heads have two eyes and two antennae.

The most important characteristics that all beetles share is their short, hard front wings called elytra. When a beetle folds its wings, the elytra cover its entire abdomen. This forms a protective shell that gives a beetle its "armored" appearance. When a beetle flies (and not all beetles do), it lifts its elytra so that its back wings can beat.

Beetles go through several stages of development called metamorphoses. Life starts as an egg. The wormlike larva emerges from the egg. The larva is the stage in which the insect eats and grows. Next the larva enters a resting stage, the pupa. Finally the pupa changes into the hard-shelled adult.

Beetles occupy a wide range of environments all over the world. They are found almost everywhere on Earth—in rain forests, deserts, mountain lakes, and even sewers. They live in every environment except the oceans. They eat almost everything, too. Some of them are herbivores, others are parasites and live in or on other animals, and many are scavengers, living on dead animals and dung. Some beetles are helpful to humans, eating other insect pests or breaking down material for decomposition. Other beetles can be harmful when they eat crops and human foods.

Bess Beetle Natural History

Bess beetles go by many names—bess bug (although they are not true bugs), betsy beetles, patent leather beetles, or palladid beetles. There are two species of bess beetle in the United States; over 500 related species are found in the tropics. They are fairly common in the Eastern United States, found in decaying logs from Texas to Florida and as far north as Canada. They are considered beneficial organisms, important in the recycling of dead wood.

Adult beetles are up to 4 cm long (about 1.5 inches), shining black with a series of grooves running the length of the elytra. Students will observe the adult bess beetle's six legs, but they may count four, rather than three, body parts. Students will discover that beetles have two thoracic segments, allowing its hard body to move more freely. Students will find a tiny, gold-colored fringe on the legs and edges of the beetle's body. The exact function of the fringe is unclear, but it may help to keep the beetle clean.

Protruding from the beetle's head between the eyes is a short horn. Most noticeable to students are the beetle's strong mouthparts (mandibles) and feathery antennae. The mouthparts allow the beetle to chew through decaying hardwood that serves as both food and shelter. (Although they look vicious, the beetle doesn't chew on anything other than decaying wood so there is no potential harm to small fingers.) The antennae "drive" the beetle. Students will observe the beetle using the antennae to explore the air. It is assumed that they use their antennae to sense odors in the environment—decaying wood or other beetles of the same species—but this has not been well-studied.

Bess beetles are somewhat social insects, living in colonies in decaying stumps and logs. They prefer hardwood—oak, elm, and other deciduous trees—that is well-decayed and falls apart easily. The beetles will chew their way through the wood, making tunnels, or galleries, as they go. In the classroom, a layer of decayed wood in a clear basin and a daily spray of water are all they need.

Bess beetles live in pairs within the colony and share housekeeping and larval care duties over long time periods. Eggs are carried through the tunnels delicately in the mandibles. Larvae are fed on a well-chewed mixture of beetle feces and wood. When the larvae pupate, which may take up to a year, they are then moved to a separate chamber for their protection. All this keeps the beetles very busy for the 14—16 months of their adult life.

Bess Beetle Communication

When adult bess beetles are disturbed, they produce a squeaking sound by rubbing their elytra against their abdomens. Students will be able to hear this stridulating. Stridulating is apparently used for communication between members of their colony and it is especially effective since most of the beetle's life is spent in darkness. Studies suggest that the sounds for defense are different than the sounds for courtship.

Bess Beetle Food

Bess beetles chew wood, and it is considered a food source but only indirectly. Unlike termites, bess beetles don't have symbiotic bacteria in their gut that help them digest the cellulose in the decaying wood they ingest. Bess beetles processes the wood through their digestive system and then a fungus grows on the beetles feces. It is this fungus that beetles eat as a food source.

Bess Beetle Mites

Eating fungus that grows on decaying wood, providing care for larvae, communicating through sounds—these are all fascinating features of the bess beetle. But they have another interesting feature—they have co-evolved with at least one kind of mite. Mites care commonly found hitchhiking on the body of the bess beetle. Some of these mites are only found on bess beetles, suggesting a relationship that has evolved along with the organisms. It's not clear that the beetles benefit from the mite, but because of their exoskeleton, they aren't harmed in any way. It may be that the mites live on secretions given off by the beetle or they may just share the decaying wood. The mites are not known to damage the beetles, don't bite or harm students, and do not leave the classroom habitat basins. Should they get on a student's hand the mites are easily brushed off.

Bess Beetle on child's finger being passed to another child's hand

Bess Beetle Investigation Summary

In Meet the Bess Beetle, Part 1: Bess Beetles at Home, students observe the beetles and learn how to handle them carefully. They become familiar with the structures of the beetle and make labeled drawings of those structures. Students set up an appropriate habitat that will provide for the needs of the beetle in the classroom. They maintain a care-and-feeding routine for two colonies of bess bugs, each in a clear basin with a cover. Students record observations over time and share them with other students.

In Part 2: Comparing Crayfish and Beetles, students observe more closely and record the beetle's structures and behaviors. Using a Venn diagram, they compare crayfish and beetles structures (both are in the phylum Arthropoda, one is an insect and other a crustacean). They discuss the functions of the various structures they observe.

In the previous sessions, students have observed how well the bess beetle can cling to a surface with their strong legs and claw-like feet. In optional Part 3: The Beetle Pull, students find out just how strong their beetles are. Using dental floss for a simple harness and paper clips for "cargo," they discover the beetles can readily pull many times their own mass. This leads to a discussion of what function such strength may serve in the beetles' survival.

Bess Beetles in the Classroom

Everything needed to conduct the new Structures of Life investigation is in the ©2000 Edition FOSS kit with the exception of the beetles and the decaying wood. The decaying wood must be supplied by the teacher. The beetles are available from Delta Education by calling 1-800-258-1302 (Monday–Friday, 8 am–6pm EST) and asking for them by name. A copy of the new investigation folio and student sheets will be sent to every school using the Structures of Life Module later this spring.

Hardy, easy to maintain, harmless, and fascinating, bess beetles have all the characteristics for a successful FOSS classroom critter.