By Nathan Welton
South Coast Beacon
a bad place to hang for the winter, especially if you’re a butterfly.
But how thousands somehow find their way there, and how countless others
flutter all the way to a small, mountainous fir forest in the Mexican
state of Michoacán, has long perplexed scientists. Now, recent
research offers a bit more insight — or just more controversy,
depending on how you see it — into the mystery of the monarch.
In a May issue of the journal Science, Steven Reppert of the
University of Massachusetts Medical School and his colleagues
reported that migrating butterflies navigate with a genetic compass,
oriented to the sun, and compensate for the sun’s changing
celestial position with a biological clock.
“Monarchs have a genetic program to undergo this marvelous, long-term flight
in the fall,” said Reppert. “They are essentially hell-bent
on making it to their over-wintering grounds.”
But Adrian Wenner, monarch-navigation dissident and UCSB emeritus professor
of biology, remains skeptical. He said he believes prevailing scientific
dogma — and
the notion that scientific journals and the media are suckers for glamour — has
prevented researchers from accepting the possibility that the insects
simply hop on jet streams and go with the flow.
“Look, do you think a butterfly can navigate for thousands of miles?” he
asked. “Navigation implies that they have in their little tiny brains
the ability to migrate across the entire United States to these groves.
“I say the monarchs are simply insects … not some exotic bird.”
Most monarchs live for only several weeks or months, but every fourth or fifth
generation, biologically different and longer-lived insects emerge from their
cocoons, called chrysalises. These butterflies are hardy enough to endure lengthy
migrations, and venture forth to a winter or summer home they, their parents,
or even their great-great-great grandparents, have never before seen.
At least, that’s what navigation theorists contend.
For several months, the insects will journey 50 to 100 miles a day
using a roadmap possibly encoded within the twists of their DNA. It
seems improbable they’d be able to find what they don’t even know they’re
looking for, but the Massachusetts study helps to explain why it’s
The team first exposed cocoons to different patterns of light and dark,
finding that light has a profound affect on the butterfly’s internal clocks.
When subjected, in the laboratory, to a normal daylight cycle beginning at
1 a.m. instead of 7 a.m., the animals would emerge from their cocoons appropriately,
in sync with the adjusted day. But when they were exposed to all-day illumination,
the butterflies emerged at random times, suggesting light can disrupt the insect’s
In order for the bugs to successfully find Michoacán’s firs, they’d
need to follow the sun, said Lincoln Brower, a butterfly expert and University
of Florida professor, and in order for them to know where the sun was in the
sky, they’d need to know the time.
Thus, the researchers needed to show that the circadian clock was tied
to the butterflies’ sun compass, so Reppert put the bugs in a flight simulator — an
enclosure with an upward air current and a rod, attached to the insect, on
a frictionless bearing — that could determine their direction while flying.
The team found that monarchs subjected to light coinciding with the East Coast
day appeared ready for a border-run, pointing southwest, toward Mexico. When
the researchers shifted the light-dark cycle six hours earlier, to one that
would mimic a more western “day,” the butterflies still aimed
toward Mexico, only this time pointed southeast.
“It’s clear that our data show that these animals use a circadian
clock and a sun compass,” said Reppert. “I think it’s great
biology, great fundamental knowledge and it may tell us something new about how
the brain works and how circadian clocks — which govern the sleep cycle — work
in the monarch.”
Although the study’s results seem intuitive and obvious, Wenner
still has some beef with the findings.
“(The paper offers) supportive evidence, sure, but only if you start with
the assumption they’re navigating,” said Wenner, making a distinction
between migration — or mass movements — and deliberate navigation.
“Monarch butterflies are magical, they’ve got a lot of mystery, and
there’s a lot of authority saying, ‘Yes, they navigate.’ So
you’ve got a brick wall of a problem here.”
While he acknowledged butterflies tagged in the United States have wound up
in Mexico, he cited evidence showing that butterflies are airborne flotsam
that fall victim to the wind, contending it would be a conceptual leap to assume
they purposefully flew there.
“Jet streams move up from Mexico and into the Northeastern states (in March
and April),” said Wenner. “So they just have to leave the trees,
hop in the winds, and bingo — they’re up in the Midwest in
no time. In the fall, the jet streams bring cold fronts back down South.”
Wenner described a scene reminiscent of someone cluster-bombing North
America with butterflies: those tagged in California have appeared
in Mexico, while others have turned up to the north, east and west — and some East Coast
monarchs have even appeared in Britain after an arduous trip across the Atlantic.
He also said scientists load the dice when they go on Mexican monarch hunts,
because they don’t look in other places, like Florida or Texas.
While Florida’s Brower acknowledges the dice may have been loaded, he
said the data is overwhelming and irrefutable that numerous insects make it
“A year ago, there was a huge (butterfly) mortality in Mexico and they
recovered nearly 3,000 tags — and low and behold they recovered them at
the over-wintering site,” said Brower. “The total number of tags
recovered last year exceeded the total number of tags collected there by a factor
of 10 since the ’70s.”
It’s all turned into a big bug brouhaha, and Wenner has a large
consensus to overcome in order to disprove the current scientific
Still, a few things are certain, according to Brower.
“Whether the monarch has a map or not has yet to be shown, but what has
been shown is that they’re capable of sun-compass orientation and time
compensation,” he said.
“We don’t fully understand how monarchs migrate to Mexico, but there’s
no question that they have the ability to use this sun compass and circadian
clock. There’s no doubt.”