Insects, due to their vast numbers, are perhaps the most understudied animal
group in the world. But Gabor Lovei, a researcher in New Zealand, remains
undaunted, having devised a fascinating new way to study beetles at night.
NOVA: Can you describe night-active ground beetles and explain what makes them
GL: Ground beetles belong to the beetle family Carabidae. They are widely
distributed, and can be found in abundance everywhere, except in deserts. There
are about 40,000 known species of ground beetles, and at least as many yet to
be described. A typical ground beetle has a proportionate body, long, strong
running legs, powerful mandibles and large eyes. Their colors are typically
black or brown, often with iridescent colors.
NOVA: Describe the greatest challenge studying this insect presented.
GL: Most species are night-active. During the day they hide in the ground or
in crevices. This, combined with their cryptic coloration makes them very
difficult to study.
NOVA: Describe the technology you use in the field.
GL: The equipment I use is called the harmonic radar, which was originally
developed to locate avalanche victims. It was first used by two Swedish
biologists, Mascanzoni and Wallin, in Uppsala for tracking invertebrate
movements around 1985. The equipment consists of a hand-held aerial with a
built-in radar wave generator, a battery, a pair of earphones and a passive
diode glued to the back of a beetle. The harmonic radar works similarly to
metal detectors. The intensity of the reflected signal is related to the
distance of the diode from the radar.
NOVA: What has this technology has enabled you to learn about night-active
GL: By following the beetles during the night, it became possible to find out
how far they move, what path they follow, sometimes what they eat or what eats
them. We found that their search path is similar to a predator search path—long "walks" (during which the beetles walk almost linearly, sometimes for
hundreds of yards) alternate with intensive "searches" of a small area.
Well-fed beetles move less than hungry ones. This proves that activity, even
during the night, is risky, so beetles that do not have to move (to eat, or to
find an individual of the opposite sex to mate), don't. Some species regularly
climb trees—it came as a surprise that more species do this than we
NOVA: Describe a typical night in the field.
GL: The beetles were collected beforehand and fitted with a transponder. The
transponder (made by soldering a diode and a flexible, fine wire coil) was
glued on the beetles' backs before taking them out to the study area. We wait
until total darkness, and release the beetles, one by one. The release points
are marked with a peg. Every 5-15 minutes, we switch on the radar, and start
searching for the beetle. We slowly walk in a spiral pattern, starting from
the last known point of the beetles' location, and make slow, sweeping motions
with the hand-held radar. Guided by the radar, the beetle is relocated, and a
new marker peg is placed where it was found. This goes on through the night—or until we fall asleep—or the battery fades. Next day we return and map
the walking path of the beetle by measuring the direction and distance of the
locations the beetle was found during the night. Then we try to find the
beetle. Sometimes the beetle remains in the field for several days, other
times it is taken back to the laboratory, and weighed to assess feeding
success. This is repeated night after night, until the end of the experiment,
or the loss of the beetle.