03-11-04

Butterflies Named for the Spring Season

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Butterflies aren't the only insects that show up during the spring season. They aren't even the first. Beetles, bees, flies and moths are all more likely to be seen flying around outside on warm, early-spring days than are butterflies. Insects reappear as the days get longer and temperatures get warmer during March and April. While butterflies aren't the first insects of spring, they are the only ones named for the season.

But they aren't called spring flies! You guessed it, there is more to the story. Once upon a time, spring was known as the butter season because that was when milk from farm animals became widely available for churning into butter. So, some of the most conspicuous flying insects got the name butterfly. Butter for the season, and fly because they flew. It probably also helped that some of the early appearing butterflies were yellow -- the color of butter.

There are lots of insects that fly, and many of them have the name fly: for example, dragonflies, damselflies and fireflies. There are also insects that scientists call real flies, the two-winged insects of the order Diptera. These include deer flies, house flies, bee flies, stable flies, and horse flies -- the list goes on and on. There are hundreds of Diptera, more than 85,000 species. Even though they are called flies, some can't. That's because there are some species of Diptera that don't have wings.

Butterflies, generally, have large, fragile wings covered with scales. Those scales come off easily, and that is why butterflies look a little beat up as they age. It is the beauty and the fragile, non-biting nature of butterflies that make them the favorite insects of most people.

Even though the name butterfly is based on the spring season, many species of butterflies don't show up in abundance until summer. A few butterflies, like the mourning cloak and the comma, spend the winter in the adult stage. But most of the butterflies that spend the winter in temperate regions do so as pupae. Therefore, when spring has sprung, most butterflies are still snug in their pupal cases.

Many butterflies do not survive winters in most of the northern areas of the Midwest. These fragile flappers migrate into the region from more southern areas. Lots of butterflies fit into this category, but the most recognizable is the monarch. The monarchs fly into all of North America from their winter sites in the mountains of Mexico. Of the spring migrant butterflies, only the monarch makes a round trip. The others just die out and repopulate each year. 

So, the first butterflies that we see each spring are those that have just emerged from hibernation or migrants from warmer, southern areas. Either way, the early season population is likely to be fairly low in numbers. High numbers of butterflies are associated with the second or third generations of the year.

What makes a good butterfly year? It isn't easy to say, but there are three important considerations. But for starters, good overwintering success, either as hibernating pupae or adults, is important. For those butterflies that don't overwinter, success in early spring populations in southern areas might determine how many adults will make their way farther north.

In addition, the availability of food plants for caterpillars is also a key. Finally, the adults must be successful in mating and in egg laying. But all of this could be offset by predators, parasites and diseases wiping out many. Or, on the positive side, nice south westerly winds to help the migrants move northward.

This much is for sure. We'll see the highest numbers of butterflies in July and August in any year. Maybe we should change their name from butterflies to summerflies!