By Carol O’Meara, Colorado State University Extension Boulder County
Gardeners, are you plagued by prickly invaders and freeloaders in your beds? Do some seedy characters come calling and refuse to take the hint and leave? Good news – painted ladies are heading to town, and with their help, you can get some relief from stress in the garden.
Painted lady butterflies (Vanessa cardui) are migrating into Colorado and large numbers of them have been spotted up and down the Front Range, according to Dr. Whitney Cranshaw, Colorado State University’s Extension Specialist in Entomology. The bug guru is eagerly anticipating a banner showing by the butterflies in what could be the biggest migration in 30 years.
Flitting in from their winter home in the Sonoran desert of the southwest U.S. and parts of Mexico, high numbers of Painted Ladies hit the road – er, air currents – thanks to good winter moisture in those areas that built up their population. Their migration moves millions of butterflies up through the USA, including Colorado. They’ve been arriving by the thousands over the Rockies into eastern Colorado in the past weeks.
Painted Ladies are often mistaken for Monarchs, due to their orange, black, and white coloration, but they’re slightly smaller and they feed on different plants (Monarchs feed on milkweed). You’ll see a lot of these butterflies for the few weeks they’re in town, as they feed on nectar and lay eggs on host plants.
Don’t expect them to stick around, though, most of them will woo us and leave us to keep moving across much of the US and Canada. Europe and Asia have their fair share of the bugs, too; Painted Ladies can be found moving about every continent on the globe, except Australia and Antarctica.
They’re working bugs, too; easy to rear, they’re released at special events like weddings. Nothing commemorates nuptials quite like setting Painted Ladies loose on the crowd.
As much as we love seeing the brightly colored, flashy butterflies dancing around the landscape. it’s the offspring they leave behind that we covet. Nicknamed the “Thistle Caterpiller, the spiny, dull-brown colored larva of the Painted Ladies often feed on thistles and mallows, which comes as good news to gardeners. In big migration years, larval numbers are high enough that the caterpillars consume the plants entirely. They also prefer common mallow, another stubborn weed.
But before you stand out in the yard hoisting aloft thistle plants as an offering to the winged wonders, hoping they’ll choose your weeds to host the offspring, take note: this usually happens only in sites where there’s a large patch of thistle. A better plan might be to carefully move some off of your lilac or hollyhock onto a thistle.
Spotting the caterpillars is relatively easy due to their penchant for privacy. Sewing some leaves close around them with silk, they feed inside the protected nest. It doesn’t take long for them to develop into adults – roughly three weeks – but several generations of the Painted Lady occur throughout the summer.
For more information on this insect, check out Dr. Cranshaw’s Fact Sheet on it at: https://webdoc.agsci.colostate.edu/bspm/arthropodsofcolorado/Painted-Lady.pdf