‘The great munching’: Caterpillars’ gluttony means food for baby songbirds

Welcome to spring, which arrived on Friday. The greening of the landscape is already well underway. Oaks, hickories, tulip poplars and other hardwoods, leafless only a week ago, are quickly donning their bright green canopies. Shrubs, wildflowers, vines and other flora already are sporting their springtime verdancy.

The rapid leafing out, in turn, is triggering another great phenomenon, the “great munching.” Between now and early fall, literally tons of voracious caterpillars will be devouring the lush foliage.

Caterpillars, of course, are the larvae of moth and butterfly species, all members of the Lepidoptera taxonomic order. Each species has its own unique caterpillar. With more than 160 butterfly species and more than 1,000 moth species, Georgia is home to at least 1,600 different caterpillars.

None is alike. They may be plump or skinny; bright colored or dull; cute or ugly; smooth-skinned or heavily spiked and hairy. Many of them use amazing camouflage and mimicry to elude predators. Most of them are harmless, but some pack potent venom that can cause severely painful stings.

They also feed only on certain plants — their “host plants.” Monarch butterfly caterpillars eat only milkweed plants; zebra swallowtail caterpillars eat only foliage of pawpaw trees; Gulf fritillary caterpillars eat only passion-vines. If there were no passion-vines, for instance, there would be no Gulf fritillary butterflies.

All caterpillars, though, have one job in common — to eat. In general, they will increase their body mass by 1,000 to 10,000 times within 10-14 days after hatching. Monarch caterpillars, for instance, grow 2,000 to 3,700 times their original mass. Their added girth provides crucial energy needed to pupate, or to form cocoons (if moths) and chrysalises (if butterflies).

When caterpillars confine themselves in these tight structures, their bodies liquefy. But over 10 days or so, they miraculously transform and emerge from their enclosures as adult moths or butterflies.

Great hordes of hungry caterpillars will be emerging between now and early fall. Right now, in early spring across Georgia, the “early risers” are the Eastern tent caterpillars (lappet moths). They are dark with a white stripe, blue oval spots and sparse hair. They build their communal silken “tents” in crotches of black cherry, hawthorn and related tree species but sometimes also in ash, birch, willow, maple, and poplar trees.

Unchecked, super-gluttonous caterpillars would denude forests within weeks. Fortunately, millions of equally hungry creatures are anxious to snatch up caterpillars by the tons to feed themselves and their babies.

They are the songbirds. Most songbirds do not reproduce on berries and seeds. Instead, more than 95% of them turn to diets heavy in caterpillars — rich in protein, soft and easily digestible — during breeding and nesting.

Other larval and adult insects — beetles, flies, crickets — also may be in their diets, but of all the insect food, caterpillars are the best sustenance for baby birds, scientists say. A single brood of Carolina chickadees, for instance, requires approximately 6,000 to 9,000 caterpillars to grow from hatching to fledgling. Parents deliver about 350 to 570 caterpillars daily to satisfy the demands of their hatchlings.

In early spring, the tent caterpillars provide much of the nourishment for Georgia’s early nesting birds such as Carolina chickadees, tufted titmice and Carolina wrens. Hordes of other caterpillar species will follow as the year progresses.