The refuges serve as pit stops on the insects' long migration - some come from as far north as Canada. They ride the wind currents, traveling up to 80 miles a day, until arriving in highland fir forests south of the border in November.
The U.S. Fish and Wildlife Service cites drought in the Midwest and a mild winter and early spring in some regions, as factors in decreasing the numbers of migrating insects. But the conservation group MonarchWatch.org says decreased butterfly numbers in recent years are due to a reduction in habitat and the move to herbicide-tolerant crops that limit the growth of the insects' staple food, milkweed.
Among the National Wildlife Refuges that lay out the welcome mat for the black and orange butterflies and people hoping to view them during their stopover:
Florida
St. Marks National Wildlife Refuge is one of the butterflies' last stops before they fly out over the Gulf of Mexico. The refuge, on Northwest Florida's Gulf Coast, sponsors a Butterfly Festival (Oct. 27 this year) timed (with luck) for the peak monarch arrival.
Virginia
The insects flock to the Eastern Shore of Virginia National Wildlife Refuge on the tip of the Delmarva Peninsula from early September to late October. The Eastern Shore of Virginia Birding and Wildlife Festival (Oct. 5-7), also gives a nod to the visiting insects.
Texas
When conditions are right, thousands of monarchs daily flit over the prairies and oak Savannahs of Balcones Canyonlands National Wildlife Refuge from late September to early October. The drought severely limited their numbers in 2011, but with winter and spring rains, refuge officials are hoping for a better turnout this year. Drop by on Oct. 13 for butterfly tagging and walks at the refuge's Doeskin Ranch.
Kansas
The monarchs descend on Kansas from mid to late September, where the Quivira National Wildlife Refuge hosts "Monarch Mania" on Sept. 15 to mark their layover. The public can take part in tagging and releasing and other monarch-related activities. Even if the winds don't cooperate, there's guaranteed viewing here, thanks to an enclosed butterfly pavilion.
Iowa
Neal Smith National Wildlife Refuge invites the public to catch butterflies for tagging at its Monarch Madness Day Sept. 8, but the butterflies can be spotted here year-round along the refuge's Tallgrass Trail.
(Copyright © 2012 USA TODAY)