CATERPILLARS ARE SCAVENGERS
by Whit Gibbons
July 15, 2007
an animal that depends on finding the carcass of a species on the endangered
species list before laying its eggs. The gopher tortoise moth does just
that, and its caterpillars dine strictly on the material that holds the
shell of the gopher tortoise intact.
tortoise is federally protected in its western range of Alabama, Mississippi,
and Louisiana. In Georgia, South Carolina, and Florida, the tortoise is
only afforded state protection but has been proposed for federal listing.
The gopher tortoise is the largest burrowing reptile in the Southeast,
making its winter and nighttime home by constructing underground tunnels
up to 10-feet deep and 30 feet long. The gopher tortoise moth, though
relatively poorly known, is an equally fascinating species as noted by
Mark and Nancy Deyrup of the Archbold Biological Station in Florida.
(people interested in butterflies and moths) work with some of the most
intriguing animals in the world. Some focus on familiar butterflies such
as the elegant swallowtails, the nomadic monarchs, and the little blue,
white, or yellow varieties that flit across the landscape. Although typically
more attractive to us, butterflies don't hold a candle to the moths in
terms of abundance. For example, butterflies have fewer than 20,000 species
worldwide compared to more than 140,000 species of moths. The more than
11,000 kinds of U.S. moths outnumber the U.S. butterflies by more than
10 to 1.
obvious lepidopterans are butterflies hovering around pretty flowers on
sunny days and moths practicing suicide missions around outdoor lights
at night where hungry spiders, bats, and treefrogs forage. But their caterpillars
hold the most unusual and bizarre secrets. Moth caterpillar lifestyles
include those that protect themselves with venomous bristles (urticating
hairs). Some caterpillars have dramatic, scary looking eyespots on their
front or back end that might keep a bird from trying to make a meal of
it. Monarch butterfly caterpillars feed on milkweeds and retain the toxic
alkaloids of the plant in their own bodies. Thus, both monarch caterpillars
and adults are protected from potential bird predators by being poisonous.
Although over 90% of caterpillars are herbivores, the diversity of plants
eaten and the ways in which they feed seem near endless. A small proportion
of the world's caterpillars are carnivorous, subduing and eating other
animals, including flies, spiders, and ants. Some even eat other caterpillars,
and a Hawaiian species eats snails after capturing them in a silk trap.
But aside from herbivory, the most common caterpillar feeding category
is that of the scavengers that make a living by eating dead animals. The
gopher tortoise moth qualifies as a scavenger specialist, along with more
infamous members of the same family, the clothes moths whose caterpillars
eat wool and fur.
for feeding on dead tortoises may be getting rarer as the big reptiles
disappear from more and more areas with development, but the gopher tortoise
moth has a plan when it finds one. The female moths are among the last
scavengers to arrive at a tortoise shell lying on the ground, the muscles,
bone, and major organs already scavenged by flies and beetles. The moths
lay their eggs at night on or near the carcass, to which the hatching
caterpillars are attracted.
of interest to the caterpillars is the protein known as keratin (our fingernails
are keratin), which binds the tortoise's large shell plates together.
Keratin provides the food for the caterpillars. But what keeps these soft-bodied
little potential prey from become meals themselves to predatory invertebrates,
such as ants, roaming the woods? Each gopher tortoise caterpillar secretes
a protective tube made mostly of silk and covered with grains of sand
that is long enough to extend from below the ground to the various seams
on the tortoise. The tube protects the creature from predators and buffers
it from hot or cold weather as it crawls to one end to eat and to the
other to retreat underground.
I said above
that lepidopterists have many opportunities for startling discoveries.
Wonder what you might find in your own backyard if you look closely enough
at the caterpillars or other insects you find?
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