MIDDLE TOWNSHIP - Pat Sutton's backyard butterfly garden teems with wildlife on a hot summer afternoon. Dozens of monarchs flirt in the air, circling one another among the trees and flowers. Tiger swallowtails drink nectar from purple and yellow zinnias. Caterpillars feast on milkweed leaves in the shade.

This scene is a far cry from spring and early June, when Sutton, a retired naturalist, literally saw no butterflies. It was the first time Sutton had seen such a scarcity in her 30 years of butterfly watching, and they did not return in large numbers to her garden until early August.

Sutton observed a similar shortage in parts of Cumberland County in late June when she volunteered for the North American Butterfly Association's annual survey, and again when she and her husband, Clay, went to the Candian province of Quebec for a vacation in July.

"It was spooky," she said during a recent garden tour. "We should have been seeing a lot more of them, and there was one of this, one of that."

Call it the case of the missing butterflies. No one knows for sure why so many butterflies disappeared, but Sutton and other people believe poor weather earlier this year may have played a large role.

Preliminary data from the North American Butterfly Association show populations in several states dropped in June and July - some as much as 50 percent - according to Jeff Glassberg, president of the 5,000 member organization based in Morristown, Morris County. The association monitors butterflies at more than 400 locations across the United States, Canada and parts of Mexico.

While tallies are still coming in and the summer counts will not be finalized until September, Glassberg said the overall numbers fell in many spots from Maine to South Carolina and west to Idaho, Kansas and Nebraska.

"I don't think we've ever seen anything like the response we've gotten this year, unsolicited, about the dearth of butterflies," Glassberg said. "It's pretty clear (the loss) is real."

The ultimate impact is unclear. But there is concern that butterfly populations will plummet again next year, according to Glassberg, setting off a ripple in the ecosystem.

Butterflies play an important environmental role as pollinators and as a food source for birds, spiders, lizards and other animals. They are very sensitive to the environment, and they require plenty of sunlight and food to thrive. Conservationists often rally around butterflies to raise wildlife awareness, and Glassberg noted the beautiful insects can reflect "the psyche of many human beings."

Glassberg theorized that the cold, cloudy climate eastern states experienced in April, May and June could have killed many caterpillars and butterflies that spend the winter as a chrysalis and made them more susceptible to diseases and parasites. The heavy mosquito boom this year prompted government officials and homeowners to spray malathion to kill adult insects. Sutton and fellow survey volunteer Jackie Parker, of Beachwood, Ocean County, fear the pesticide could have harmed butterflies.

The caterpillars that transformed into adults earlier in the season would have had a difficult time surviving. "In the rainy weather, (butterflies) are sitting ducks, cannot fly and we had so much rain this spring that even if they did emerge, they couldn't find a mate and lay eggs for the next generation," Sutton said.

Scientists such as Jaret Daniels, an assistant entomology professor at the University of Florida, warn that butterfly numbers can change for a variety of reasons - such as hurricanes and wildfires - and the public should look at data from multiple years before drawing any conclusions from this year's NABA counts.

Yet Daniels noted many butterflies that used to be common decades ago are dwindling across the country because of human development in their natural homes, especially in wetlands, prairies and high-density locations such as Florida and Southern California. If butterfly habitats continue to shrink, Daniels said aggressive conservation action would have to be taken to keep the populations stabile and the species that will most likely be around in the future will be the ones that can adapt to urban settings.

Jamie Cromartie, an associate entomology professor at The Richard Stockton College of New Jersey, said the Atlantic County butterfly population did not have a big drop when he and other volunteers worked on the count this year. But Cromartie noticed that some common species came out in fewer numbers and he attributed it to the weather.

Cromartie said he believes aggressive roadside grass mowing, "manicured lawns" replacing weedy fields with native plants and the reversion of old fields into forest is contributing to the decreased abundance of butterflies and other insects.

NABA volunteers such as Sutton and Theresa Knipper, a Princeton master gardener who worked on the five surveys throughout the state, including Atlantic, Cape May and Cumberland counties, noticed the butterflies started coming back in mid-August when the temperatures rose again. But both women said the numbers weren't as high as in previous years.

To help the butterflies, Knipper, who spends her summers in Cape May, suggested planting flowers such as milkweed, asters and goldenrod to lure the insects and provide plenty of food.

Sutton encouraged people to grow native plants in their backyards or in planters if they live in cities to boost the native butterfly populations. Sutton pointed out that many butterfly species lay their eggs on such common trees as oak, black cherry and sassafras, and she called the woods behind her home "a nursery."

"I hope the butterflies out now are able to mate and create enough butterflies for next year," Sutton said.

If not, Sutton could face an empty garden again next spring.

E-mail Michelle Lee: