Life

Incredible Creatures: Invasion of the painted ladies

John Gavloski

 
This particular Painted Lady, spotted in Carman this month, is one of the unusually high number of these butterflies flocking to Manitoba this year. (JOHN GAVLOSKI)

This particular Painted Lady, spotted in Carman this month, is one of the unusually high number of these butterflies flocking to Manitoba this year. (JOHN GAVLOSKI)

Many know of the annual migrations of Monarch butterflies. But there are other butterflies that can also have quite impressive migrations. In this month’s Incredible Creatures we will explore a colourful butterfly that travels a long way to get to Canada, and this year has arrived in impressive numbers in Manitoba. This is the painted lady butterfly (Vanessa cardui).Whether driving down the road or working in your garden, you can’t miss seeing a lot of these orange, black and white butterflies this year.

The incredible journey

Painted ladies are attractive orange, black and white butterflies. When they perch and fold their wings the undersides of the wings are also quite interesting, with the hindwing having a row of 5 eye-spots (figure 2). Sometimes small blue pupils are even present in these eyespots. Birds intent on eating them may try to peck those eyes instead of the body, which is less damaging to the butterfly.

Painted lady butterflies are known for their distinct migratory behavior. Adults migrate into the Prairies from overwintering sites in the southwestern U.S. and Mexico. They often arrive in June, although in some years they can be entirely absent. Periodic increases in populations of these butterflies at their overwintering sites can initiate mass migrations of adults northwards. This year the migration north was very large.

Painted Ladies have tremendous powers of flight and individuals are capable of flying a thousand or more miles. So the butterflies can rapidly repopulate most of Northern America during spring and early summer.

These northern migrations appear to be partially initiated by heavy winter rains in the desert where rainfall controls the growth of larval food plants. Painted lady migration patterns are highly erratic and they do not migrate every year. Some evidence suggests that global climatic events, such as el Niño, may affect the migratory behavior of the painted lady butterflies, causing large-scale migrations.

There is evidence of possibly some degree of return migration in the fall. One study described their migrations as potentially strong in the spring in years when populations are high, and weak or not at all in the fall. There is no evidence that they can survive our cold winters.

Painted lady butterflies will feed on nectar from many plants including thistles, sunflowers, pearly everlasting, burdock and knapweed. We often see them feeding on the flowers of the purple coneflower plants we have in our yard.

Thistle munching caterpillars

The larval stage of painted lady butterflies are called thistle caterpillars. One of their preferred things to live on and eat is thistles. They will feed on many other plants as well, occasionally getting to noticeable levels in crops such as soybeans and sunflowers. When they first hatch from the eggs these caterpillars are small and black, and will begin to eat immediately. As they grow they will shed their skins three times, this is called a molt.

Each stage in between a molt is called an instar. So thistle caterpillars have 4 instars. At each instar the caterpillar will need much more food as it has expanded in size. If under stress they will sometimes shed into a fifth instar, which is a very large caterpillar. A fifth instar is a sign that something is not ideal, such as what they are eating. The molted skin sometimes appears as a black speck, which looks like dirt, near the caterpillar. Occasionally the molted skin will look like an entire, dead, caterpillar, as snake’s skin does.

Larvae build a nest by producing a loose webbing which at times may result in the leaves being folded or tied together. The larvae have long spines on each segment of the abdomen. These spines do not contain poison and are not sharp.

Once the caterpillar stage is complete they will spin a patch of silk and attach their hind end to the silk. It then begins changing internally and becomes a chrysalis. The chrysalis can be dark or light colored depending on conditions during development of the caterpillar. It takes 7–11 days for the chrysalis to turn into a butterfly. There are two generations of this butterfly in Manitoba.

Winged livestock

Painted lady butterflies are quite easy to raise. This has resulted in businesses being established that rear and sell painted lady butterflies that can be purchased and released at events such as weddings, birthdays and memorials. And caterpillar kits can be purchased for classrooms and home schooling. One such business is Lucy’s butterfly farm based in Ontario. There are also places that do annual releases of painted lady butterflies as part of festivals and other events.

I had fun rearing some of these butterflies in my lab this year from caterpillars collected off crops. When the butterflies emerge there is a red liquid that is present in the cage that looks like blood, but it is not. This red liquid is called meconium, and the butterflies use this fluid to pump up their wings. They need to pump up their wings and dry them before they are fully functional. So for anyone who may enjoy rearing caterpillars at home, don’t be alarmed when you see this red liquid as the butterflies emerge.

So watch for these colourful butterflies, they shouldn’t be hard to find. You are witnessing the descendants of what was quite a spectacular migration this year. It is a rare event to see them in numbers like we have this year. They could be around until about early-October. So enjoy this spectacular natural phenomenon.

Incredible Creatures is a monthly contribution to provide information on some of the common yet often not well known creatures that we share space with in Manitoba. John Gavloski is an entomologist living in Carman.