Thursday, August 6, 2015

How Long Do Butterflies Live?

Back in September of last year, our Life Sciences team set off to find out how long do butterflies live. For our first study we chose Idea leuconoe, the paper kite. It was a species of butterfly that we could recognize easily and that would show markings well.

The results were surprising and have led to further studies on additional species.

To track the butterflies, we used paint marker to uniquely identify all the butterflies that emerged each day. The color and number of spots were specific to a date of emergence. When the butterflies died, we collected them, noted the paint marks, and calculated their length of life. For many, many weeks, we continued to have marked butterflies floating about the exhibit. As we watched the butterflies, we began to notice all kinds of interesting behaviors:

• Paper kites roost in large groups at night and during rest periods in the day. They like water and occasionally would have to be rescued from the pond.

• As butterflies go, paper kites are pretty aggressive. They can’t harm other butterflies, but they are quick to pursue them and drive them out of feeding spots.

• They have very strong preferences for certain flowers where they both feed and rest.

As weeks became months, we realized that Idea leuconoe had the potential to live much longer than we originally thought.

Our next step was to study two other species: Morpho peleides, the blue morpho and its relative M. polyphemus, the white morpho. We thought these two butterflies would have a pretty similar life story, but it turned out as we marked and observed them that the blue morpho was seen in more types of environment around the exhibit and was more often seen eating. The white morpho seemed to have very limited places it was found and they were often the species driven off by paper kites!

Collecting the butterflies after they died and logging their survival dates was a lesson in patience. With all three species, we had a sizeable group that only lived a handful of days, a bunch that lived an intermediate length, and a few outliers with extremely long lifespans.

With numbers such as this, the median is the best measure of what is really going on. At the median, half the butterflies in the group live longer and half live less long. This protects our numbers from reflecting the very long lives of a few extraordinary individuals.

This study brings up some interesting questions.

• What is going on at the short end of the life spans? Why are some of the butterflies only living a few days? Is this something we can change or are we observing individuals that appear healthy but have hidden issues?

• What is going on at the long end of the life spans? Are some butterflies ‘SuperAgers’ or did they just somehow happen upon all the resources they needed? Is that resource something we can provide for the whole population?

• What should we look at next?

Life Sciences has already begun studying another genus, the Caligo, owl butterflies. Maybe you’ll see some with markings? And then – maybe one of our smaller brightly colored species. Do smaller butterflies have shorter lifespans? Maybe it’s time to find out!

While everyone in Life Sciences worked very hard to mark, collect, photograph, and record the data a special shout-out goes to former Animal Caretaker Whitney Pennington who crunched the numbers, analyzed the records, and created the graphs. Her examination made it possible to answer questions as they came in and gave us confidence that the numbers have real meaning. Thanks, Whitney!

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