Used as an alternate to land snails in: Structures of Life (2nd edition, CA edition)
Bess beetle – Odontotaenius disjunctus
Background. One out of every four animals in this world is a beetle. Poke around in a field, under the surface of the ground, in trees, gardens, rotten stumps, or wood piles, and you are likely to run into a beetle of some sort. We may know them as hungry munchers of grain supplies or house foundations, but they serve vital roles in the food web as scavengers and decomposers. In the classroom, they take on the starring role in students’ investigations into structure and function.
Bess beetles are classified in the insect order called Coleoptera. Coleoptera is the largest order of organisms, including over 350,000 species. With so many opportunities, you are sure to know several. Ladybird beetles, fireflies, scarabs, and darkling beetles (the mealworm adult stage) are all Coleoptera. They all have hard, shell-like forewings, or elytra, from which their name is derived. In Greek, koleos means "sheath,"and ptera means "wing." This unique structure functions as a tough protector of the beetle's delicate hind wings and soft abdomen. When the beetle decides to fly, the hind wings unfold and do their job. At rest they tuck themselves back under the hard elytra. These tough elytra also protect beetles as they squeeze through narrow passageways and burrow into decaying wood or sandy soil.
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 usual six legs and three body parts common to all insects. Some students may identify four body parts on their beetles. They have just discovered another characteristic of Coleoptera, which have two thoracic segments. Like a knight in articulated armor, the thorax of this beetle has two sections, allowing its hard body to move more freely.
If you look for information on bess beetles, you'll find that they have several aliases. Betsy beetle, bessbug, patent leather beetle, and passalid beetle are all names for a beetle commonly found in decaying logs from Texas to Florida and as far north as Canada. They are considered beneficial organisms, important in recycling dead wood. There are only two species of passalids in the U.S., while over 500 species of passalids can be found in the tropics.
A bess beetle has tiny, gold-colored fringe on its legs and on the edges of its body. The exact function of the fringe is unclear, although it may help keep the beetle clean. Protruding from the beetle's head is a small horn. Most noticeable to students are the beetle's strong mandibles and feathery antennae. The mandibles allow the beetle to chew through the hardwood that serves as both food and shelter. It will rarely bite the hand that holds it. In the unlikely event it does, it is more of a surprising nip than a bite. Antennae "drive" the beetle. Students will observe the beetle using 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, with colonies living together in decaying stumps and logs. They prefer hardwood—oak, elm, and other deciduous trees—that is well decayed and falls apart easily. The beetles chew their way through the wood, making tunnels, or galleries, as they go. In the classroom, a layer of decayed wood in a high-walled basin and a daily spray of water is all they need.
Life cycle. All beetles go through several stages of development called metamorphosis. Life starts as an egg. The wormlike larva emerges from the egg. The larva eats and grows. Next the larva enters a resting stage, the pupa. Finally, the pupa changes into the hard-shelled adult.
Unfortunately, maintaining a reproducing colony is not easy. One difficulty is distinguishing males from females, hard to do based on external observations, although females tend to be a bit larger. Another difficulty is keeping adult pairs in an undisturbed container so they can construct a family burrow system. Bess beetles are very sensitive to air movement, almost more so than light, so every time the decaying hardwood is replenished, the beetles will be disturbed. Bess beetles live in pairs within the colony and share housekeeping and larval care over long time periods. They delicately carry eggs through the tunnels in their mandibles. Larvae eat a well-chewed mixture of beetle feces and wood. When the larvae pupate, which may take up to a year, they are moved to a separate chamber for their protection. All this keeps the beetles very busy for the 14–16 months of their adult life.
When adult bess beetles are disturbed, they produce a squeak by rubbing their forewings (elytra) against their abdomen. Students will be able to hear this stridulating. Stridulating is apparently used for communication between members of the colony, and it is especially useful because most of the beetle's life is spent in darkness. Studies suggest that the sounds for defense are different than the sounds for courtship. The larvae also make sounds, using a different mechanism.
Eating. Bess beetles chew wood, which is indirectly a food source. Unlike termites, bess beetles don't have symbiotic bacteria in their gut that help them digest the cellulose in decaying wood. Bess beetles process wood in their digestive system, and then a fungus grows on the beetles' feces. It is this fungus that give beetles nourishment.
Mites. Eating fungus that grows on decaying wood, providing care for larvae, communicating through sounds—these are all fascinating features of bess beetles. But they have another interesting feature—they have coevolved with at least one kind of mite. Mites are commonly found hitchhiking on the body of the bess beetle. Some of these mites are found only 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 find protection from the beetle while they 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 mites get on a student's hand, they are easily brushed off.
What to do when they arrive. Keep the bess beetles in a well-ventilated plastic container, provide them with decaying hardwood from oak, elm, or other deciduous trees (no conifers), and mist the wood and container several times a week to maintain the moisture. It may also help to keep some sphagnum moss on top of the wood to maintain the moisture. Hardy, easy to maintain, harmless, and fascinating, bess beetles have the characteristics for a successful classroom critter.
A Bess Beetle Investigation is available. This investigation, called Meet the Bess Beetle, was 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. **See the Structures of Life 2nd edition FOSSweb page to download the Bess Beetle Alternative Investigation.
What to do with them when the investigations are completed. Give the bess beetles to another teacher conducting the module or return to the district science coordinator for distribution to other schools. Bess beetles should never be released into the wild as they can compete with local organisms and disrupt the environment. If you have collected bess beetles locally then you can return them to the location where they were found.