We’re all to blame for the cankerworms, naturalist says

Cankerworms, it is their time of year

Their leaf munching weakens trees making them more vulnerable to age, drought, other insects and disease.
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Their leaf munching weakens trees making them more vulnerable to age, drought, other insects and disease.

Insecticides that killed migratory birds and development that robbed them of habitat help explain why Charlotte’s cankerworm population has grown over the decades, a noted Carolinas naturalist said.

“One probable culprit is insecticides that, overused by homeowners and government agencies alike, empower cankerworms over time to develop resistance to these noxious chemicals,” said Bill Hilton Jr., executive director of Hilton Pond Center for Piedmont Natural History in York, S.C., and author of “The Piedmont Naturalist.”

More important, however, “is the startling loss of spring migrant songbirds that for millennia had stopped by the Carolina Piedmont going north, and it’s not coincidental spring bird migration coincided exactly with the time of cankerworm emergence,” Hilton said. “Native birds—from warblers to orioles to thrushes, and the like—fueled their migratory flight by consuming huge numbers of energy-rich cankerworms and other larval insects.”

“Not anymore,” Hilton said. “National Audubon Society reports that populations of even some formerly widespread bird species have declined by 80 percent since 1967, with many others dropping by 50 percent. The Society’s namesake, John James Audubon, in the mid-1800s described insect-eating birds ‘dripping from the trees’ during spring migration, a sight we will never see again in North America.”

The Observer reported this week that cankerworms are slinking once again on Charlotte’s trees, feasting on leaves and plopping into the hair of unsuspecting walkers and joggers.

Some Dilworth residents reported plucking the little green caterpillars off their heads and clothes this week in what has become perhaps the grossest harbinger of spring in some Charlotte neighborhoods.

Cankerworms typically emerge this time of the year from eggs laid by wingless moths in December. Their population has grown for 30 years in the Queen City, city officials have said.

Their growing population has long stumped entomologists, but Charlotte’s large number of old willow oaks could help promote their rising numbers, city officials say on the city’s online cankerworm Q & A page.

To which Hilton responded: “If those entomologists are also environmentalists and ecologists, they would know two likely causes for the increase in cankerworms in and around Charlotte.”

“Our bird loss has come about, in large part, because of poisoning by those very pesticides used to kill insects, but mostly from habitat destruction on both ends of the migratory path,” Hilton said. “Migratory songbirds were natural, no-cost exterminators of those pesky cankerworms that now are so abundant because too often we humans haven’t been very good environmental stewards.

“Too many cankerworms? They’re largely our fault, so learn to live with them.”

Kevin Shally, who retired after 26 years as a Charlotte landscaper, recalled how cankerworms emerged within three or four years of the city shooting off loud booms and taking other measures to rid the Myers Park and Eastover areas of starlings in the 1980s. The birds feasted on cankerworms, but they created a mess on people’s lawns with their waste, he said.

City of Rock Hill officials teach others how to band a tree. The banding of trees creates a barrier between the ground and tree leaves, preventing female cankerworms from laying eggs. This do-it-yourself video can help residents learn about tree b

Joe Marusak: 704-358-5067, @jmarusak