The tragic cause of all those cankerworms

Cankerworms invade the Charlotte region every spring. Humans killing off bird habitats is one reason.
Cankerworms invade the Charlotte region every spring. Humans killing off bird habitats is one reason.

Just as the coming of cankerworms is an annual spring event, so is big coverage of these ubiquitous caterpillars. Thus, I wasn’t surprised by your April 12 front-page article (“Those cankerworms are emerging on trees – and landing in people’s hair”).

What did surprise me was the article’s last paragraph, which includes this phrase about the cankerworm epidemic: “Their growing population has long stumped entomologists...”

If those entomologists are also environmentalists and ecologists, they would know two likely causes for the increase in cankerworms in and around Charlotte. One probable culprit is insecticides that, overused by homeowners and government agencies, empower cankerworms over time to develop resistance to these noxious chemicals.

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. Native birds – from warblers to orioles to thrushes – fueled their migratory flight by consuming huge numbers of energy-rich cankerworms and other larval insects.

Not any more. National Audubon Society reports that populations of formerly widespread bird species have declined by 80 percent since 1967, wth 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.

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. 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.

Hilton is is executive director of Hilton Pond Center for Piedmont Natural History in York, S.C.