Heavy rains bring a burst of white butterflies

Large southern white butterflies flutter around a Limber Caper plant. (Photo Gail Karlsson)

Although some years there are hardly any butterflies, this November there have been hundreds of Great Southern Whites fluttering around my house. Although not all are white. You can see the dark edges of the wings on top and the underwings tend to be different shades of yellow.

Some people say they feel like they’re walking into a Disney movie when the butterflies swoop in, and up close, the butterflies’ faces look a bit like cartoon characters.

The great southern white butterflies have distinctive turquoise antennae tips. (Photo Gail Karlsson)

Where do they all come from? It seems like a miracle when they appear, and of course, in a way it is. This year I have been trying to learn more about what is going on with them.

They can sometimes be seen over water, and there are some types of southern white butterflies that do migrate, at least for short distances. However, those here Ascia munuste eubotea – They are autochthonous and non-migratory. But they are definitely seasonal.

Many insects have seasonal cycles of activity and then appear to disappear when environmental conditions are unfavorable, such as when the weather turns cold in the north. On the islands, it is the dry season that makes life difficult for insects, and some have learned to wait out droughts at various stages of development.

In the case of these white butterflies, their eggs appear to go into a kind of dormancy called diapause during the dry season, and then revive and hatch when it rains heavily again. This is when many of the plants also enjoy rapid growth buds, and some plants and trees will also produce flowers as part of their own reproductive cycles. Those flowers provide nectar that feeds the new butterflies, while the butterflies in turn provide pollination services for the plants. Synchronization makes the ecological system work.

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One of the main host plants for Great Southern White butterflies in the Virgin Islands is the native Limber Caper. Host plants often have chemicals on their leaves that make caterpillars and butterflies unpalatable to predators.

When I went out looking in the yard, sure enough, I found little patches of tiny yellow eggs on top of some of the flexible caper leaves.

The yellow dots on this Limber Caper leaf are tiny butterfly eggs. (Photo Gail Karlsson)

When the eggs hatch, the caterpillars eat the leaves. If there are enough leaves on the plant, the caterpillars thrive and the host plant is not significantly damaged.

Snapper capers are important host plants for Great Southern White butterflies in the Virgin Islands. (Photo Gail Karlsson)

Some of the nimble capers appeared to be overloaded with caterpillars and chewed leaves, while others were relatively intact.

This caterpillar had eaten enough leaves and was ready to transform into its pupal stage of development. (Photo Gail Karlsson)

I brought one of the larger caterpillars inside to see what it would look like when it pupated. I thought with all those butterflies around there would be a bunch of pupal boxes outside, but I only found one empty box hanging on the bottom of a leaf.

The caterpillar I brought inside soon finished eating caper leaves and wasted no time in starting to transform into a pupa.

Shortly after I brought this caterpillar inside, it began to pupate, in preparation for becoming a butterfly. (Photo Gail Karlsson)

Then, about 10 days later, a new butterfly emerged, with only a few days to fly in the sun, drink nectar, find a mate, and produce new eggs.

The only times these butterflies stay still for more than a few seconds is when they gather to drink from puddles or wet areas. Then when they get closer, sometimes one thing leads to another and the cycle of life continues. Until the days dry up again.

Butterflies cling back to back when they find a mate. (Photo Gail Karlsson)

When the rainy season has passed, there seems to be a point at which the egg-producing butterflies receive an environmental cue and release neurohormones that somehow initiate diapause in the eggs they lay. Those eggs will be resistant to desiccation and will wait quietly until the next rainy season arrives before springing into action.

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The process really seems miraculous.

Gail Karlsson is an environmental lawyer, writer and photographer. She is the author of two books on the Virgin Islands: The Wild Life in an Island House, and Learning About Trees and Plants: A Project of the Unitarian Universalist Fellowship of St. John. She has also recently published A Birds’ Guide to The Battery and New York Harbor. Follow her on Instagram @gailkarlsson and gvkarlsson.blogspot.com.

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