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The New York Times
My Alerts: Evolution
June 15, 2010 5:27 AM
--------------------------------------

Science: Insects That Can't Beat Them, So They Scare Them
By SEAN B. CARROLL
Researchers  discovered moths and butterflies that display
patterns mimicking those of predators.

June 14, 2010



*Insects That Can’t Beat Them Scare Them*

*By SEAN B. CARROLL*

Imagine that you are a one-half-ounce, two-inch-tall insect-eating bird
foraging for dinner on the dimly lighted floor of a Costa Rican rain
forest<http://topics.nytimes.com/top/news/science/topics/forests_and_forestry/rain_forests/index.html?inline=nyt-classifier>.
You come face to face with a pair of beady eyes. Study them for a moment.

If those eyes belonged to a snake, that moment of study would mean that you
would be dinner by now.

The face, however, is not a snake’s, but the chrysalis of a skipper
butterfly. An uncanny resemblance — but, as it turns out, not a unique
disguise.

In one area of Costa
Rica<http://topics.nytimes.com/top/news/international/countriesandterritories/costarica/index.html?inline=nyt-geo>alone,
a team of researchers led by Daniel H. Janzen and Winnie Hallwachs of
the University of
Pennsylvania<http://topics.nytimes.com/top/reference/timestopics/organizations/u/university_of_pennsylvania/index.html?inline=nyt-org>and
John M. Burns of the Smithsonian National Museum of Natural History
have
discovered hundreds of species of moths and butterflies whose caterpillars
or chrysalises display false eye and face patterns that mimic those of
snakes, lizards or other animals. In a study published this week in
The Proceedings
of the National Academy of
Sciences<http://topics.nytimes.com/top/reference/timestopics/organizations/p/proceedings_of_the_national_academy_of_sciences/index.html?inline=nyt-org>,
they propose that this plethora of counterfeit patterns has evolved to
exploit birds’ innate instinct to avoid potential predators.

The idea is a fresh twist on the well-established phenomenon of mimicry
among animals. First described by the British explorer Henry Walter Bates in
the 1860s (the subject of my
column<http://www.nytimes.com/2010/02/16/science/16crea.html?scp=1&sq=Imitators%20That%20Hide%20in%20Plain%20Sight,%20and%20Stay%20Alive&st=cse>on
Feb. 16), the original insight was that harmless, edible species could
gain protection from predators by resembling distasteful, noxious species.

Bates assumed that for this mechanism to work, the potential predators had
to learn which prey in their range were to be avoided. And the potential
prey — say, a large, colorful adult butterfly — must closely resemble the
inedible species it mimics.

But when it comes to a deadly encounter with another species, there may be
no second chances, no opportunity for learning. Hence, natural selection
would favor instant recognition, and hard-wired rapid responses, in a close
encounter with potential danger. Harmless creatures that evolved some
general resemblance to the variety of creature features to be avoided (eyes,
scale patterns) would then gain some protection

Dr. Janzen and colleagues have cataloged a delightful assortment of striking
false eye patterns on the front and rear ends of caterpillars and the front
ends of chrysalises.

Their bounty and insights are the product of a dedicated, and somewhat
accidental, long-term study of the denizens of the Área de Conservación
Guanacaste, or A.C.G. <http://janzen.sas.upenn.edu/>, in northwestern Costa
Rica.

It began in 1978, when Dr. Janzen broke some ribs falling into a ravine
while conducting field studies in the region. The road to the hospital was
too rough to navigate, so he wrapped his sore rib cage and confined himself
to a chair for a month.

Unable to explore the rain forest, he soon went a bit stir-crazy. The field
station had only two hours of electricity each night, and just enough power
to run a 25-watt light bulb. Fortunately for Dr. Janzen, that was a bumper
year for moths, which were attracted to the light. So he passed the time
building a moth collection.

When he recovered enough to wander back into the rain forest, he discovered
that it was also a bumper year for caterpillars. The challenge was to
identify which of the many different kinds of caterpillars belonged to which
species of moths or butterflies. Now 71, he told me from his field station
32 years later that “my private insanity was to find all of the species
before I die.”

To accomplish his goal, he had to set up a system of collecting the
caterpillars, photographing each of them, raising them into adults, then
identifying each of the species, at least half of which had not been
described previously. He started by himself, then was joined by his wife,
Dr. Hallwachs, an expert on rodents and now caterpillars. The operation
continues to this day, 365 days a year, with the help of 33 trained Costa
Rican assistants.

In an area of about 77 square miles, more than 450,000 caterpillars have
been studied. As of a few years ago, the team had identified more than
12,000 species. That number ballooned to 15,000 species when the team
discovered, through the use of DNA typing, or “bar coding,” that many of the
species were actually made up of multiple distinct species, as many as 11 in
one case <http://www.pnas.org/content/101/41/14812.full>. The total number
of species in just this one region equals that of all of the moths and
butterflies species of North America.

With caterpillars and chrysalises coming into the station at the rate of
more than one hundred a day, Dr. Janzen began to discern a trend. In species
belonging to many different groups, he saw caterpillars or chrysalises that
bore all sorts of paired eyelike markings of various color schemes, with
round or slit pupils. The variety of patterns suggested that the bugs do not
have to match exactly the appearance of any particular predator for the ruse
to work.

Moreover, the distinct behavior of many caterpillars when handled
underscored that the whole game was to startle the many species of
insect-eating birds that foraged in the dry, cloud and rain forests of the
conservation area. Some eye patterns became visible only when the
caterpillars were molested and expanded part of their body, and some large
specimens wriggled and rattled like snakes.[image:
15CREA-span-articleLarge-v2-1.jpg]

Dr. Janzen and his colleagues estimate that a typical foraging bird might
encounter tens to hundreds of false-eyed bugs each day. It is unlikely that
a bird encountering such a spectrum of patterns could learn to discern which
specific ones were safe and which were not, especially when one mistake
would mean its demise. It would be better to leave suspicious items alone
and to quickly move on.

For two centuries, naturalists have sought to catalog and make sense of the
dazzling diversity of life, particularly as found in the tropics. Often, new
insights have come from asking very simple questions, like “Why does this
small caterpillar look like a snake on one end?”

But the answer to such questions requires finding many more creatures and
understanding where and how they live. And that requires a special breed of
human willing to live far from the comforts of home and eager to look at
450,000 bugs for 32 years.


Martin





Full Story and nice image of scary (not really) caterpillars:
http://www.nytimes.com/2010/06/15/science/15crea.html?emc=tnt&tntemail1=y

-- 
–––––––––––––––––––––––––––––––––––––––––
Martin Weiss, PhD
Science Interpretation, Consultant
New York Hall of Science

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