Naturespeak A naturalist's view of the world

May 24, 2009

Pump’n Up a Polyphemus

Filed under: Uncategorized — wykes @ 6:41 pm

I discovered a Polyphemus moth cocoon this past winter (see here) and decided to leave it in place  for the duration of the season. It was in a “conspicuous” place , at least for me to find it again, but still cryptic enough so that I felt a hungry woodpecker or mouse wouldn’t get to it. I finally collected the silken wrapped package about three months ago and hung it up in my unheated back porch. Last year I had the good fortune to find  and eventually hatch out a beautifully plump female moth and I awaited this late May season with great anticipation (see earlier Naturespeak).

The moth that magically appeared yesterday morning was not a female, but was a magnificent male – one of the largest I’ve seen in some time (see above). In the world of giant silk moths the females are usually the largest but this robust male was giving the gals a run for the money. Male moths possess a huge set of feathery antennae (see below) and are easily identified because of this. Those sensitive organs can pick up individual hormone molecules sent by distant females and it’s likely this guy had already netted a few love notes. He made his entrance late on the previous evening and was ready to try a run at those gals by the time I met up with him.  It was up to me to open the door and let him go.

Large silk moths like this can’t just fly away on demand, however. When first contacted they instinctively drop to the ground, flare their wings, and flop around for a bit. In doing so, they expose a pair of intimidating “blue eyes” (see below) on their back wings in an effort to scare the potential predator. The bluffing attempt buys some valuable time – extra minutes to live and extra minutes to charge up their flight batteries. Like many insects, they need to warm up their muscles before flight is possible. This feature is called obligate heterothermy. 

I carefully grabbed the moth’s wings between my forefingers and thumb, before it had a chance to drop (see here), and carried it outside. The events which followed provided an opportunity to see how a Polyphemus gets up to speed. Take a good look at this video sequence here and you’ll see  the  essence of the “drop, flop, shiver, and fly” routine. Once the moth drops to the ground it flops about – apparently at random, but actually well performed so as to keep the eye spots facing up.  The third stage, the shivering part, generates internal heat. Depending upon the species, this required temperature is around 95 – 102 degrees F.  Who says insects are “cold-blooded?”

Experiments on captive moths have shown that the duration of this shivering activity depends on the surrounding temperature. If the ambient temperature were 95 degrees, for instance, the shiver time would be minimal. It was 60 degrees F on this morning and it took about five minutes for this moth to reach the proper take-off heat. I eventually picked it up, expecting it to drop again, but it finally broke free and quickly flew off. Flight itself generates the heat needed to maintain the critter’s cabin temperature at the proper level and the furry coating of body scales acts as an insulating layer to hold it in.

I watched the Polyphemus gain height and vanish over the tree line. I’ll admit that I half expected a Flycatcher to swoop down and engage it in aerial combat, but this did not occur. I can only imagine that this hot-blooded creature found a secretive hideout where it could wait out the hazards of the day before charging up for an exciting night of hormonal bliss.

1 Comment »

  1. I love your blog. I found a Polypohemus Moth in my yard and was trying to see what type of creature it was. I stumbled on your site and it is beautiful. I love your amazing writing as well as the stunning photos. I am curious if my moth is a male or female, what attracted it to my yard, are they common in Bouniful, Utah, etc…. Can you give me any info if I email you the photo I took?

    Thanks1
    Christy

    Comment by Christy — June 23, 2009 @ 8:53 pm

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