The monarch butterfly is famous for its annual migration to the mountains of central Mexico.
But the creature's lifespan can be a matter of weeks, so the ones that fly south in the fall are not the ones that come back in the spring.
So how do they know where to go? In 2002, Queen's University researcher Barrie Frost found that monarchs use an internal clock and the sun to tell them.
Now, he and Jeremy McNeil, an entomologist at the University of Western Ontario, are investigating how they know when to stop.
“They use the same sites, year after year,” says Dr. McNeil, an expert in the reproductive strategies of migrating insects, and they may smell their way.
Butterflies eat milkweed, which contains noxious compounds and may give their waste a distinctive and long-lasting odour to guide the way, he explains.
Last month, he was at the Monarch Butterfly Biosphere Reserve, about 125 kilometres west of Mexico City, collecting air samples he and his colleagues plan to analyze and compare with samples from forest areas where the insects do not congregate.
The reserve is vital because all monarchs east of the Rockies winter in Mexico (the westerners head to California), where deforestation threatens their habitat.
The government created the butterfly haven in 1986, and last November, President Felipe Calderon announced a plan to curb illegal logging within its borders. However, satellite photos released this month show that clear-cutting is still taking place.
Conservationists say thick, old-growth forest is required to help the monarchs avoid freezing in the mountains. Millions have died after severe storms, as recently as 2004.
But the sanctuary was set up without consulting the local people, who are poor and relied on wood from the forest to build furniture, cook their food and keep warm themselves. More recently, however, many have begun to earn money by catering to the growing number of tourists who now come to see the butterflies.
Dr. McNeil understands better than most what draws the visitors. The first time he saw how the black and orange monarchs cluster on the trees in the tens of thousands, he says, the hair on his arms stood on end.
“If you believed in fairies, you would think that is what you were looking at.”
