|
back to organism index
BESS BEETLES
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, formally known as Odontotaenius disjunctus,
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.
Back to top
|
