Do butterflies get wet in the rain?

Dear Charleigh,

Whenever there’s heavy rains or winds, butterflies seem to disappear. This is because butterflies hide when it rains. That’s what I found out from my friend David G. James who is an associate professor at Washington State University. He studies insects, including butterflies, in the Pacific Northwest.

When a storm comes in, different butterfly species hide in many unique places. Some butterflies sit low, down in grasses or flowers, while others go into bushes and trees. Some butterflies like to roost in vegetation beneath large trees. The leaves of these trees intercept raindrops and reduce the impact on the butterflies below.

Butterflies are also much smaller than you and me. An average monarch weighs roughly 500 milligrams and large raindrops have a mass of 70 milligrams or more. According to Scientific American, a raindrop this size striking a monarch would be equivalent to a human being pelted with water balloons weighing as much as two bowling balls.

If a butterfly does get wet, it simply stays still until the water evaporates off their body. Butterflies often bask in the sun to dry their wings.

The Zebra Longwing Butterflies, like to find shelter in the company of one another during the evening or periods of rain. When they are all together and showing off their bright stripes, it makes them easy to spot.

Rain can be annoying for some species, including aquatic animals. During extremely hard rain storms, other animals such as frogs, turtles, and fish disappear to the depths of lakes and ponds or try to seek shelter under rocks, driftwood, and aquatic plants.

James said that if you want to attract butterflies to your yard it’s best to plant nectar-producing plants that are native to where you live. You should also make sure your butterfly garden includes shrubs, tall grasses, trees, dead branches or rock piles for shelter.

If you come across a resting butterfly, resist the urge to touch it. It will move when it is nice and warm. We don’t want to risk damaging wings with our fingers. If you can spot them, let me know where you see butterflies hiding from the rain where you live.

Sincerely, Hannah Welzbacker (and Dr. Universe)

Hannah Welzbacker contributed this article. She is a student in the Edward R. Murrow College of Communication at Washington State University.

Michael Raupp, professor of entomology at the University of Maryland, offers this answer.

Imagine a monarch butterfly searching for nectar or a mate in a meadow on a humid afternoon in July. Suddenly, a fast-moving thunderstorm approaches, bringing gusty winds and large raindrops. For the monarch and other butterflies this is not a trivial matter. An average monarch weighs roughly 500 milligrams; large raindrops have a mass of 70 milligrams or more. A raindrop this size striking a monarch would be equivalent to you or I being pelted by water balloons with twice the mass of bowling balls.

Amateur and professional lepidopterists tell tales of butterflies darting into protective vegetation and scrambling beneath leaves when dark skies, strong breezes and the first raindrops signal an imminent storm. During heavy rains and wind, butterflies are rarely seen. Not only does rain pose a direct threat of injury or death, but the cool air associated with storms may also reduce temperatures below the thermal threshold for butterfly flight. In preparation for flight, these aerial acrobats expose their wings to direct sunlight, which rapidly warms their flight muscles. Overcast skies limit their ability to gather the solar radiation needed to take wing. A butterfly knocked from the air by raindrops thus faces the double threat of crashing in an inhospitable habitat where predators lay in wait and being unable to warm its body sufficiently to regain flight. Little wonder, then, that when skies darken, butterflies seek shelter in their nighttime homes.

Butterflies are quiescent when it is dark and take refuge in protected locations called roosts within one or two hours of sunset. Roosts may be tall grasses, perennial herbaceous plants, tangled thickets of woody shrubs, undersides of large leaves, caves or, in some cases, man-made objects such as fences or hanging baskets. Butterflies may also roost in the vegetation beneath overhanging trees. The leaves of the upper canopy intercept raindrops and reduce their impact on vegetation and butterflies below.

Several species of neotropical butterflies, such as the zebra butterfly, Heliconius charitonius, roost in the company of their peers. Perhaps as a result of the good company, Heliconius exhibits curious fidelity to roosts, often returning to the same location or individual plant for several nights. When rain threatens, zebra butterflies enter their nocturnal roosts much earlier than they would on clear days. And, like us humans, they demonstrate considerable lethargy on rainy mornings, delaying their usual early departure by as much as several hours. Unusually long stretches of rainy weather may even reduce the population of butterflies in a roosting group, because cool temperatures hinder their mobility and therefore their ability to escape from predators.

Ultimately, what butterflies do in the rain is avoid it. But with the return of sunshine following a summer shower, they often resume patrolling and courting within minutes. So the next time the sky darkens and thunder rumbles, take a cue from the butterflies. Find a safe roost out of the rain, but as soon as the sun returns, go out and enjoy.

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