Yes, there are tigers in northeastern Wisconsin, some that
hunt their prey by day, others by night. Their eyesight is very
excellent when they are not running too fast, and they use their
amazing speed and fierce, sickle-like jaws to bring down their
victims. Fortunately they are not four-legged mammals but rather
six-legged insects, tiger beetles.
Delve briefly into the field of entomology and you’ll find
that beetles, in the order Coleoptera (co-lee-OP-ter-a), comprise
around 40% of all animals on Earth, easily the largest of all
orders. It was Oliver Wendell Holmes who said, "No man can
truly be called an entomologist, sir; the subject is too vast for
any single human intelligence to grasp."
Fortunately there are only around 147 different species of
tiger beetles in North America with some species considered to be
critically endangered. Beetles in general can be easily
recognized by the tough, armor-like forewings, called elytra
(EL-eh-tra), that cover the softer hind wings that are used for
flying. Observe a tiger beetle at rest and you will see that
their elytra usually meet in a line down the middle of the back.
The order name, Coleoptera, means "sheath wings" and
refers to the elytra (eleytron is singular).
Starting around the middle of June and usually extending into
early August I see the brilliant, metallic-green, six-spotted
tiger beetles, between one-half and five-eighths inch long, on
our driveway especially on sunny days during my daily walk out
to the mailbox. Just for the fun of it I occasionally try in
vain to run one down. I’ll usually get to within three feet of
the swift running beetle before it takes off and flies about ten
more feet ahead of me down the driveway. After three or four
bursts of flight the beetle tires and makes a quick short flight
off into the adjacent tall grasses.
Professor Cole Gilbert, Cornell University entomologist, has
intensively studied tiger beetles and learned that one is capable
of running at a speed 53.87 of its body-lengths per second,
amounting to about .53 meters per second. This speed of
approximately 25 miles per hour for short bursts is relatively
(per body size) 10 times faster than our best human sprinter.
Tiger beetles are considered to be the fastest land insects in
the world.
Professor Cole has also learned that frequently these beetles
stop-and-go as they pursue their prey, the reason being that the
beetle’s ability to see shuts down after it accelerates toward
its victims. When moving too quickly they don’t gather enough
photons to form an image of their prey and they have to slow
down.
Couple this voracious beetle’s great speed with its
strongly-toothed sickle-like jaws and its prey victims stand
little chance of escaping. Numbered among its many victims are
aphids, lice, fleas, bugs, caterpillars, ants and worms. These
amazing beetles, however, do have their own predators such as
dragonflies, other larger tiger beetles, birds, spiders and
robber flies.
Quite often I lift the wooden lid covering an old bathtub at
our garden, used to store and warm water for watering young
plants, and there will be one or more six-spotted tiger beetles
frantically swimming around, trying to escape. I simply scoop
them out with a hand and give them their freedom.
With my digital camera set for a quick image recently, I
released one of the fast-moving beetles onto the wooden tub lid
and, surprisingly, it slowed down temporarily along the edge of
the cover for just one picture before flying away. Since then
I’ve learned, fortunately not by experience, that some tiger
beetles are capable of inflicting very painful bites. Caution is
the word in case you wish to handle one of these colorful
insects.
In general, tiger beetles are very alert and active, may be
recognized by their big "bug" eyes, swift actions,
large, pointed, very sharp mandibles, antennae that arise from
the top of the head, long spindly legs that hold the body well
off the ground, narrow thorax and broad, almost oblong elytra.
Colors range from brilliant green, violet, or orange to grayish
and black. One of the most beautiful of all the world’s species
is the Japanese tiger beetle. Invariably tiger beetles will have
at least a few white spots on their elytra.
Most tiger beetles are diurnal, sun-loving species. However,
adults will often burrow into sand or loose soil at night and on
very hot days. Some species live on bare, hard-packed ground,
especially on cultivated land, plowed fields and even along city
sidewalks.
They go through a complete metamorphosis consisting of the
egg, pupa, larva and adult. The highly carnivorous larvae live
in tunnels from which they attack their unsuspecting prey.
Located on the lower backs of the larvae are hooks that anchor
them to the side of the burrow while they subdue their prey.
The beautiful tiger beetles serve to show the value of even
the most barren spots on the planet. Remember, all that glitters
is not gold -- it may be a dazzling green, six-spotted tiger
beetle.
A dazzling green beetle, common in
this region, is the fast-moving voracious, six-spotted tiger beetle.
This column appeared in the Door County Advocate
on 07/19/2003.
© Copyright 2003 Roy Lukes. All rights reserved.
