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A Chance Encounter

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A Chance Encounter

After many decades of gardening I had the pleasure of experiencing something new this spring.  While raking mountains of leaves out of my perennial beds, an odd shaped object caught my eye (upper right image).  As I picked up the smooth, light brown, oval form I soon realized I was holding a large cocoon.  This one was intriguing since it was so much bigger than others I had seen in the past.  I could hear the pupa inside rattle like a maraca and had no idea if it could be alive.  I took it to the Plant Doctor Desk here at the Kemper Center for Home Gardening and soon learned that what I had found was the cocoon of a polyphemus moth and it was most likely viable.

With the help of expert Plant Doctor Ronda and the internet, I educated myself regarding the life cycle of these magnificent creatures.  The polyphemus moth, Antheraea polyphemus, is one of our largest and most beautiful silk moths (upper left image). It is named after Polyphemus, the giant Cyclops from Greek mythology who had a single, large, round eye in the middle of his forehead. The name is fitting because of the large eyespots the moth has in the middle of its hind wings (lower image).  These eyespots are believed to startle predators and the moth displays them when disturbed.  The wingspan of an adult averages 10 to 15 cm – or up to 6 inches.

The species is widespread in continental North America, with local populations found throughout Canada and the United States.  Larvae feed on leaves of broad-leaved trees and shrubs including birch, grape, hickory, maple, oak, willow and members of the rose family.  The caterpillar can eat 86,000 times its weight at emergence in a little less than two months and though this sounds daunting, polyphemus caterpillars are never found in sufficient numbers to cause significant damage to their host trees (except occasionally in California where they may be pests in commercial plum orchards.)  Their populations are also regulated by natural enemies - including insect parasitoids and predators.

I decided to hang on to the cocoon in the hope that it was viable and I could see the moth emerge.  I found a suitably large jar to keep it in and put it on my outside porch so that nature would control when the moth emerged and a mate would be available.  My research determined that the expected time of emergence for this area would be between May and June.  To my delight, an adult male polyphemus moth emerged two weeks after I found the cocoon and I was able to get this photo (lower image) that same evening before I set him free.

Polyphemus moths mate the same day that they emerge from their cocoons and mating usually occurs during late afternoon or evening.  Females emit pheromones, which can be detected up to a mile away to attract mates.  A female will lay her eggs shortly after mating.  If unsuccessful in recruiting a male after 2 or 3 days, a female will stop calling and release her unfertilized eggs.  As adults, polyphemus moths live a maximum of only 4 days.  Their entire life cycle averages about 3 months in length.  This includes about 10 days as eggs, 5 to 6 weeks as larvae, 2 weeks as pupa and about 4 days as adults.  In the case of my polyphemus moth, it overwintered as a pupa in its cocoon which increased its life cycle length.

Gardening never fails to present us with opportunities for enjoyment and learning.  Sometimes life’s simple pleasures come in little packages – or big cocoons!

Jan Gowen, Kemper Horticulture Assistant

Posted in: Summer | Tags: caterpillar , butterflies , nature | Comments (0) | View Count: (2888)
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