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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Swallowtail butterflies 'puddling' on a gravel road. © Gregory K. Scott
Swallowtail butterflies 'puddling' on a gravel road.

© Gregory K. Scott

August 2001

Drinking parties

When butterflies sip, sip, sip, it's in a puddle!

Anita Carpenter

Drinking parties. The phrase brings to mind groups of friends packed together at corner taverns watching their favorite teams on big-screen televisions, telling jokes and swapping stories.

On a gravel road the morning after a rain, sippers of a different type cluster around mud puddles and damp areas. Tens to hundreds of butterflies gather in an activity known as mud-puddling, puddling, drinking parties or bachelor parties. It is a curious behavior whose function is little understood.

About ten o'clock one early August morning along the Larsen snowmobile trail, I was a bystander watching hundreds of sulphur butterflies puddling. Once a butterfly selected a damp area, others quickly joined it. All faced the same direction with wings closed and tilted perpendicular to the sun's rays. Each butterfly was positioned to stay out of its neighbor's shadow. Some of the sulphurs seemed to be resting and soaking up the warmth, while others extended their proboscises and actively engaged in drinking. For such an unusually frenetic species, the pace of activity seemed relaxed.

Why does puddling occur? No one knows for certain. Many butterfly species feed on flower nectar that provides ample sugar and energy, but is very limited in necessary minerals and ions. Research suggests that the moisture or urine on gravel roads contains dissolved minerals and salt ions, in particular sodium, which may stimulate reproductive development or activate a temperature regulating system to help the young butterflies heat up and keep their cool.

Only newly hatched males puddle, hence the name "bachelor parties." Older males and females do not participate. And only species like sulphurs and swallowtails, whose males patrol territories, engage in puddling. Species like hairstreaks and coppers, whose males perch waiting for females to approach, do not puddle.

The largest drinking party I saw that morning contained about 50 individuals crowded into a square-foot area. Although I carefully avoided disturbing them, the cluster took flight as I approached. What a feeling to have 50 buttery-yellow sulphurs flitting about my face. If only other butterfly species could be as plentiful as these are!

I returned to the trail one week later. The puddling was over, but the "party" was still in full swing. Males were actively chasing females. If all went well, there will be more young males bellying-up to the mineral bar for another round of drinking parties next year.

Anita Carpenter revels in nature's gatherings in every season. She writes from Oshkosh.