Critters: Grand Valley is chock full of hornworms & hummingbird moths |

Critters: Grand Valley is chock full of hornworms & hummingbird moths

A small, clear-winged sphinx moth is seen feeding on a flower.
Bob Hammon |


Hornworms found feeding on tomatoes can be controlled by garden insecticides like carbaryl, permethrin and spinosad. Another biological control organism that can be used is Bacillus thuringiensis (dipel and thuricide). Or remove pest worms by simply picking them off by hand; they are commonly found feeding on the outside part of tomato plants around dusk or dawn.

SOURCE: Colorado State University Extension Fact Sheet No. 5.517

Editor’s note: “Critters” features insects, spiders, snakes and other freaky/fun creatures unique to the Grand Valley. Have a critter you want discussed? Email

See a four-inch caterpillar with a rear-end spine, you’ve just spotted a Colorado hornworm; with many local species (30 across the state), this prevalent Grand Valley critter will morph from beast to beauty in a matter of weeks.

According to Bob Hammon, Colorado State University Extension’s western Colorado entomology expert, hornworms can grow “as big as a finger,” and most are not considered pest species. The tomato hornworm, however, is considered a garden muncher.

“The caterpillars chew leaves, and plants can be rapidly defoliated,” a Colorado State University Extension Fact Sheet said. “Fruits may also be chewed. Tomatoes are particularly susceptible to injury; but other related plants, such as peppers and potatoes, are occasionally infested.”

Once mature, hornworms become an even more noticeable hummingbird, hawk or sphinx moth — some very colorful, flying during the day, while others only come out at night.

“These moths have a superficial resemblance to hummingbirds in flight while they similarly feed from deep-lobed flowers,” the fact sheet explained. “The whitelined sphinx is the species most commonly observed in this habit and is usually most active during late afternoon and dusk. The great ash and twinspot sphinx are two other species commonly observed in ‘hummingbird moth’ behavior. Adults of most hornworms (including the ‘tomato’ hornworms) fly after dusk and are rarely observed except occasionally at porch lights.”

And, like birds and bees, hummingbird moths are considered to be active pollinators, overall good for gardens and flowers in general.

“I see them every day in flower gardens,” Hammon said. “They’re avid nectar feeders, with a tongue like a straw that coils up.”

For more information about Grand Valley critters, reach out to Hammon at

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