JEFFERSON CITY - Monarch butterflies, some of whom migrate more than 2,000 miles to winter in Mexico, are moving through Missouri by the thousands this fall.
Monarchs are unique among butterflies because of the long-distance migration.
Mike Brown, entomologist for the state Department of Agriculture, said he has seen more monarchs this year than in the past.
"That's just the ones I've seen in my garden," Brown cautioned. "But it's not an official count."
Scientists estimate that tens of thousands of monarch butterflies will pass through Missouri. Overall, more than 100 million butterflies will make the trip to Mexico. The migration season lasts from August to late October.
The annual migration highlights one of the world's environmental concerns.
Researchers have warned that logging around the small forest in Mexico that is the monarchs' destination may threaten the insect.
Also, a few preliminary studies have found indications that larval-stage monarch caterpillars may be at risk from genetically-modified corn pollen.
Milkweed is the only food source for larval monarchs, and it's commonly found in and around corn fields.
A study by Laura Hansen-Jesse and John O'Brycki at Iowa State University found that milkweed plants that had been exposed to genetically-modified corn pollen had 20 percent of the monarch larvae die. None of the larvae on regular corn died.
"This isn't going to wipe out monarchs in the Midwest, but it's something that needs to be considered in the future debate," O'Brycki said.
Other researchers take a different view.
"These studies don't cause me to be alarmed right now," Brown said. "What concerns me is they haven't done any studies on this with conventional corn and conventional insecticide."
While the debate rages, others are more concerned with tagging and tracking monarch populations.
Linden Trial of the University of Missouri's Department of Conservation Biology said she started tagging monarchs in late August.
The small tags, about the size of a pen tip, are placed on the underside of the butterfly's wings, she said. The tags are numbered and labeled with the location, age and sex of the monarch.
"The furthest I've had one picked up is in Jefferson City," Trial said. "But I know of others in Missouri who have had tagged monarchs tracked all the way to Mexico."
Of course, the biggest threat to the monarch may be represented by the splats that appear on the windshields of cars throughout Missouri this time of year.