URBANA, IL -- Small mysterious pollinators have been visiting late-summer and fall-blooming plants in our gardens in order to sip nectar, said University of Illinois Extension horticulture educator Kelly Allsup. With wings as fast as a hummingbird and long tongues like a butterfly, these small moths hover over flowers to gather nectar.
In the fall months in Illinois, hummingbird moths, a member of the sphinx moth species, are numerous and most come out close to dusk, Allsup noted.
"There are 60 species of sphinx moths, and the most common ones are the white-lined sphinx moth, clear-winged sphinx moth, five-spotted hawk moth, and Carolina sphinx. These moths are almost as large as hummingbirds and also fly during the day," she said.
The color of the white-lined sphinx moth is mottled gray, brown, and white with pink bands. The clear-winged sphinx moth or hummingbird moth, is a large moth much smaller, about 1 inch long, with clear wings that mimic a bee.
"Although cherished as adults, the five-spotted hawk moth and Carolina sphinx incite murderous rage in their larval stage to any gardener trying to grow tomatoes," Allsup said. The five-spotted moth and Carolina sphinx's larvae, also known as tomato hornworm and tobacco hornworm, are large green caterpillars that grow about 4 inches long and about as big around as a fat man's thumb."
These caterpillars can demolish a tomato plant in just a few days. "The first sign of them is the bare branches and stubs at the tips of the plants that have been stripped by these ferocious eaters," Allsup explained. "Although they are large, they are just the right color to blend in with the foliage. A small horn at the end of their abdomen distinguishes them from other caterpillars and provides a menacing façade for any predators."
Allsup added that four weeks after hatching from the egg, the hornworm begins its pupal stage by dropping to the ground to burrow. "This time of year, they will remain in the pupal stage throughout the winter. This is why it is necessary to clean up tomato debris and disc-till the soil in order to destroy them in the pupal stage," she said.
"There is no need to address hornworms with pesticides. Instead pay the neighbor kid 50 cents a worm to pick them off the plants and feed them to chickens and other birds," Allsup said. "Or leave them on the plant and let nature take care of the problem for you."
Parasitic wasps often lay their eggs on the bodies of the hornworms where their larvae hatch and feed on the hornworm. After the larvae have mortally eaten the caterpillar's insides, they emerge to decorate the hornworm with their white cocoons. "If you find a tomato hornworm with white bumps all over it, leave it alone. The parasitized caterpillar will stop feeding and soon die," Allsup said.
Newly hatched wasps will seek other hornworms in the vicinity to lay their eggs.
Even in their larval stage, they are considered a garden pest, but hummingbird moths are a treat to see in the garden, Allsup noted. "To attract them to your garden, plant lots of fall-blooming perennials, create a water source, and skip the pesticides. Then sit back and watch these lovely pollinators make your fall garden home," she said.