Invasion of the butterflies!

There’s an invasion throughout the Front Range creating flashes of orange – and this time we aren’t talking about Bronco fans. Painted-lady butterflies, which are sometimes mistaken for monarchs, are showing up in Colorado in higher-than-usual numbers, creating a flutter throughout area parks and open spaces.

Michael Weissmann, Ph.D., MSU Denver affiliate professor of biology, entomologist and co-founder of the Butterfly Pavilion, shares his expertise on why the latest migration is showing these large numbers.

Why are painted-lady butterflies more numerous this year than in an average year?

They occur year-round in the Sonoran Desert area of northwestern Mexico, southern New Mexico, Southern California and Arizona. Typically, if this area has a damp winter and low parasite load, it can see sporadic population bursts. As they start to run out of plant resources that the caterpillars like to feed on, the butterflies look to move. These changes act as the catalyst that influences the butterfly to migrate north beyond standard levels. This migration is how we re-establish our painted-lady population each year in Colorado and further north. In an especially good year, there will be large numbers moving north.

It is also possible that the conditions in Colorado were more favorable this year with warmer, wet weather in early spring producing a lot of caterpillar food-plant and nectar sources locally. Consequently, we can often see a local explosion of the population, especially when parasite and disease levels are low.

Does the painted-lady butterfly migrate?

While we have more definitive research studies detailing the migration patterns of the monarch butterfly, we have very little proof of the instinctual migration of the painted-lady butterfly. However, we do know that when the population explodes in the Sonoran Desert and food supplies are depleted, they historically will move north.

Have we reached the peak point of activity and population in Colorado this season?

How far can painted-lady butterflies migrate?

We have very little research on the migratory capabilities of the painted lady. We do know that the monarch can go all the way from Canada south to Mexico, but they don’t come all the way back north in the spring and will often hang out in New Mexico and south Texas. Some research has shown that the painted ladies can migrate up to 9,000 miles from England down to Africa, but the majority of this is done over multiple generations of the butterflies’ life cycle.

When is the best time of year to spot the painted-lady butterfly?

It depends on the year, but typically there are big bursts of them when the lilacs are blooming in May. This year has been unusual with the fall migration, and the butterflies are concentrated on area rabbit brush. On campus, they are feeding off trees that have aphids on them since they drink the honeydew that the aphids excrete.

Why aren’t we seeing butterflies at the levels that we used to?

The primary reason we have seen the reduction in butterfly populations is the fact that natural habitats have been reduced. Many people immediately think of pesticides, but in fact use of chemicals has had a very minor impact compared with habitat reduction. We still have too many parking lots and homes with bluegrass lawns. The concepts of nectar gardens, green roofs and open-space parks have been positive steps in the right direction.

Should people consider planting milkweed and other butterfly-friendly plants in their gardens?

Yes. We have created a very sterile urban environment that isn’t conducive for butterfly populations. We need to move away from the grow-it-to-mow-it mentality. By planting nectar sources and caterpillar-friendly plants, you can help the population at both ends. Milkweed is just one source to help the monarch caterpillar. Plant parsley to support the black swallowtail, chokecherry for the tiger swallowtail, thistle for the painted lady. You can’t have college kids without kindergartners, so plant for the caterpillars, not just the butterflies.

Maintain nectar throughout the year by making sure you have something for each season: a lilac for the spring, a rabbit bush for the fall and a butterfly bush for the middle of the year. You want to have continuous blooming throughout the garden not just so it looks nicer, but it will also better support butterflies and caterpillars as well. To protect insects from weather, plant gardens on the south side of the house to avoid northern winds, providing morning sun and evening shade.