The Dragonfly Mystery

This week I posed my biology students a challenge.  They were to look at the organism below and try their best to say what it was, using observation, questioning, a testable hypothesis, and an idea for an experiment to test their hypothesis.

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What is this little monster?  A cricket?  Some kind of spider?  

I laid eight small piles of these exoskeletons on the lab desks and had students circle around to look at them.  The ones I provided have a tiny, torn hole just behind the head, and there are no insides.  They range from 2 to 3 centimeters, with the largest nearly 4.5 cm long and 3 across, including the legs.  They are truly hideous little creatures, and at least one girl screamed in each and every class.

What did students observe?  They noticed that they were, first of all, insects because they have 6 legs.

Good start.

They also observed that they are "dead," because they are dried up and not moving.  To this I responded that these were not alive, but it was not really correct to call them "dead."

"Are these real?"

"Yes, these were real organisms."

"Can they bite you?"
"Well, not now.  But they were at one time voracious predators.  Vicious killers, actually."

"Where did you get them?"

"Up north, around Walloon Lake in early August."

"YOU MEAN THEY LIVE HERE?!"

Students most frequently proposed that these are dead crickets, or some, with more precision and subtlety, suggested that these were the exoskeletons shed by growing crickets.

Close, really close!

Finally, in my last hour, a single student working by herself called me over.

"Mr. Nolan, I think I know what these are.  We looked at them in water quality at Seneca Middle school last year."

"What are they?"

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Yes!  These are the shed exoskeletons of dragonfly nymphs just after they had crawled out from the lake- by the millions and millions- in early summer in northern Michigan.  The grown nymphs crawl out of the water; after a few hours the thorax puffs up and splits behind the head, and the massive shoulders of the dragonfly thorax thrust through the leathery skin.  It arches its back, burdened with tightly compressed and crumpled wings, out of the nymph skin in an eerie imitation of a charmed snake.  Then its head arches back and its wings slowly- so slowly- inflate from their raisin-like shape into broad, papery air foils.  Its broad, squat abdomen pulsingly creeps out of the exoskeleton and telescopes into a narrow rod, drying and turning a bright greenish yellow with every passing moment.

Finally, after several hours of painful metamorphosis, the dragonfly extends its wings and clumsily flitter-flutters away.  

This description of the origins of dragonflies is utterly baffling to the students.  It is, at the same time, deeply satisfying to witness their realization that many common critters have similarly surprising origins.

There is a whole galaxy- a whole universe- underlying the commonly held understandings and misunderstandings in the minds of young people.  Show a student this universe and she may recoil at first in disgust, but soon she leans in until her nose is pressed against it and she falls in, without self-consciousness or pride,only the perfect humble joy of wonder.