Where are all the monarchs this year?

A big clump of pink-flowered swamp milkweed is in full bloom in Pat Reynolds' Plymouth rain garden, and a little girl from next door has been eagerly running to check it each day for the black, yellow and white-striped caterpillars that usually munch on the plants before becoming monarch butterflies.

So far this year, only four caterpillars have been found. Last year, Reynolds, her grandkids and neighbors collected 25 caterpillars to put in jars so they could witness their miraculous transformation.

"You just don't see them this year," Reynolds said.

Gardeners' e-mail lists have been buzzing about the scarcity of monarchs in the Twin Cities this year.

The wildlife hot line at the University of Minnesota's Bell Museum has been peppered with "Where are the monarchs?" calls.

Observers in prairie areas north of the Twin Cities, where dozens of monarchs usually flit, report seeing only a few this year.

Experts say the monarchs' low numbers aren't caused by the butterflies' shrinking winter habitat in Mexico, but by cold, wet springs here and in Texas and Oklahoma. Our recent extremely dry weather hasn't helped, either.

"This is one of those species that deals with adversity quite well, and the population can rebound very quickly," said Taylor, a professor and insect ecologist at the University of Kansas. "I'm more concerned about what happens in Mexico this winter. If overwintering conditions are poor with a small population, it takes longer for the population to rebound."

Karen Oberhauser, an associate professor at the University of Minnesota who runs the Monarch Larva Monitoring Project that relies on volunteers to submit monarch data from all over the country, said population reports from the Upper Midwest are running below average.

Problems started early

"I just talked to a volunteer in North Dakota who has a prairie filled with beautiful milkweed," Oberhauser said. "In a normal year, she sees dozens of monarchs. This year, she's seen one egg and three larvae."

Taylor said the problems started earlier this year, when a fat and healthy crop of monarchs left Mexico in March to begin their migration north. Exceptionally cold weather hit Texas and the Southwest through the first half of June, just as the first new generation of monarchs was beginning to migrate. Those butterflies typically mature in April and fly all the way to Minnesota and even Canada over a six-week period.

"I think relatively few reproductive monarchs reached the northern parts of the range," Taylor said.

Oberhauser said she saw three monarchs in her big perennial garden in Roseville last week. But she cautions that individual observations can be misleading.

"Gardens are just a fragment of habitat, and there may be some years when monarchs just don't find a garden," she said.

Oberhauser will analyze data from her monarch count in September. With natural predators, drought, cold and rain all preying on monarchs -- Oberhauser said 90 percent don't survive past the small caterpillar stage -- their marathon migration seems even more miraculous.

While early monarch generations born in Minnesota live only about a month, dying after they reproduce, Oberhauser said any butterflies that emerge here after about Aug. 20 will live eight to nine months, migrating back to the high, cool forests of Mexico. There they hang from trees in colonies all winter, moving back to the southwestern United States in March to lay their eggs before dying.

Reynolds, a retired elementary-school teacher, said so many schools teach units on the monarchs that it may be the only butterfly some people can identify. She follows the monarch migration on websites that track the insects as they move north. This spring, she said, it was evident when the weather stalled their migration.

She isn't surprised that people notice when monarch numbers are down.

"Think of those little delicate wings and how far they go!" she said.