Gardeners have set a place at the table for butterflies and their caterpillars, but no one's coming to dinner.

In the last few weeks, homeowners who populate their gardens with host and nectar plants for butterflies have been wondering to themselves – and in the last few days, out loud to experts – why they're seeing so few species fluttering about. No one's supping from the pentas; no caterpillars are munching away at the parsley planted expressly for them.

Is there a mysterious malady in the making? According to North Texas entomologists and lepidopterists, it's merely nature taking its natural course.

NATALIE CAUDILL/DMN

Question mark butterfly

"Last year was a very unusually abundant year for Lepidoptera ," says Dr. Mike Merchant, a Dallas-based entomologist with Texas AgriLife Extension. "I kinda stamped last year as the year of the caterpillar."

"All the species are here that are normally here," says Dallas County butterfly farmer Dale Clark. "It's just that the numbers are way, way down. This is the normal ebb and flow of insects. They rise, they drop. This year it's just barren."

Mr. Clark, 49, raises caterpillars and butterflies in his Glenn Heights back yard to supply museum exhibits and other events. Something is killing his hand-raised creatures this spring, despite painstaking efforts to sanitize the insects' habitat and butterfly farming equipment. But Mr. Clark does not believe the ailment striking his farm-raised inventory is related to the dearth of naturally occurring butterflies that visit his insect-friendly flower beds.

"Last year was the best butterfly season I've seen in 20 years," says Mr. Clark, who has been interested in butterflies since first grade. "But the population of predators also increases," because of the extra food source.

Both Mr. Clark and Dr. Merchant recently have heard from area gardeners asking if something's amiss. Mr. Clark says queries are not limited to North Texas, that he's heard from "the Hill Country, West Texas, just all around."

"I don't want people to think butterflies are doomed," he continues. "Just because you're not seeing them doesn't mean they're not around. They're here."

Dr. Merchant concurs. "When we have a year of great abundance, like last year, by the end of the year the parasites and predators have built up, too. Their numbers would be even greater this spring.

"This year has been so normal, weather-wise. I can't imagine there's something so ubiquitous it would affect everything."

Mr. Clark advises gardeners to continue to provide nectar sources for butterflies. Pentas, zinnias, garden phlox and tithonia are standards, because their broad flowers provide a good landing pad. Also offer host plants on which butterflies will lay eggs. Black swallowtails prefer dill, parsley and fennel; gulf fritillaries like native passionvine ( Passiflora caerulea).

"This is sort of out of our hands," says Mr. Clark. "We have butterflies emigrating northward from Mexico and South Texas until the first frost. Insect species can repopulate very quickly."

The butterflies may be late for dinner, but they'll show up eventually, he says.Online