PROVIDE ECOLOGICAL MYSTERIES
is a time for caterpillars, and those of the imperial moth are showy
and impressive - big around as a thumb and as long as a finger, with
formidable looking spikes on the body. Yellow spots resembling portholes
are on the body segments along the sides. The one we found was a cinnamon
orange color. Many are bright green.
admired the huge caterpillar wearing its gaudy costume as it crawled
onto my hand. I knew it would soon weave a cocoon, enter the pupal stage
underground and later turn into a magnificent yellow-and-purple imperial
moth, a member of the silkworm family.
didn't know about them was more extensive. Why was this one reddish
instead of green? Why do they have little hornlike protuberances on
the head? What is the function of the yellow spots? You don't need to
understand the biology of a plant or animal to wonder and speculate.
and toads, moths and butterflies lead a double life. Caterpillars and
tadpoles are dramatically different in appearance, feeding habits and
other aspects of their ecology from their adult forms. And scientists
are a long way from understanding all of the ecological factors involved
in that transition.
of some, perhaps most, insects is complicated. Clearly they have many
secrets to reveal, and their small size makes certain observations difficult.
The wide variety of caterpillar shapes, colors and ornamentation reinforces
the idea that their ecology and behavior are highly complex. Research
on a seemingly unimpressive western caterpillar supports this conviction.
The study also demonstrates how a single scientist can discover an intriguing
Erick Greene conducted a study on the larvae, or caterpillars, of a
small southern Arizona moth that lays eggs on oak trees. The moth has
two life cycles during a year, laying eggs that hatch into caterpillars
in spring that become moths in summer. These then lay eggs that become
caterpillars later in the summer. This behavior is not particularly
unusual. What the caterpillars do in the two different seasons is.
hatch in the spring feed on the male flowers, catkins, of the oak trees.
The caterpillars not only eat the catkins but also look almost exactly
like them. Thus when a caterpillar is having a meal, it looks like the
food it is eating - great camouflage for a caterpillar that might otherwise
be a tasty morsel for a bird.
about the larvae that hatch in the summer, a time when the catkins are
gone? To look like a catkin on an oak tree that has only leaves and
twigs would be like inviting a bird to dinner. Well, sure enough the
moth has a different strategy for that time of year.
eat leaves instead of catkins, and they quickly assume the shape, texture
and brown color of a tiny oak twig. The caterpillars from the two different
seasons do not vary genetically, so an obvious ecological question for
the investigator to pursue was, how does the caterpillar know whether
to look like a catkin or a twig?
feeding experiments, Greene found that the season a caterpillar was
born was not important. Instead its future appearance was determined
by what it ate. Caterpillars he fed catkins began to look like catkins,
even in summer, when catkins would not normally be present. Those fed
leaves, which have a different chemical composition in that they have
tannins (that are absent in catkins), began to mimic twigs.
As we continue
to uncover such intricate ecological strategies in something as simple
as a moth, we realize how much we do not know. How many wonderful discoveries
are out there waiting to be revealed? With greater understanding of
ecosystems and their interconnecting parts, we learn to appreciate our
natural environments. And the really pressing questions remain: Why
are some imperial moth caterpillars cinnamon orange instead of green?
And what on earth is the purpose of those yellow portholes, other than
to look pretty?
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