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.... an orange and black rampaging shapeshifter for your Halloween Daily Bucket ....

wb road
The Daily Bucket is a regular feature of the Backyard Science group.  It is a place to note of any observations you have made of the world around you.  Rain, sun, wind...insects, birds, flowers...meteorites, rocks...seasonal changes...all are worthy additions to the bucket.  Please let us know what is going on around you in a comment.  Include, as close as is comfortable for you, where you are located. Each note is a record that we can refer to in the future as we try to understand the patterns that are quietly unwinding around us.

late October, 2013
Pacific Northwest

I've been seeing these vivid Halloween colored Woolly Bear caterpillars often crossing the roads here lately. That means we're deep into fall, and frosts will be upon us here in the Pacific Northwest any time.

In the fall, this caterpillar is on the move seeking a suitable overwintering spot - like under a rock or bark - to wait out the cold, until it can crawl out next spring, pupate, and fly away as the Isabella Tiger moth (Pyrrharctia isabella). Very soon after the moths mate and lay eggs, new caterpillars will hatch and start crawling around for the rest of the warm season, until next fall.

Some cool and unusual facts about the Woolly Bear:

!  It overwinters as a caterpillar rather than as an egg or pupa.

!   It can freeze solid and then thaw out, no harm done, because of a cryoprotectant in its body fluids.

!   It is a generalist, feeding on pretty much any herbaceous vegetation.

 !  It needs to grow and molt 6 times before it can pupate, so in cold climates, with their short growing seasons, there isn't enough time to complete all 6 in one year. The Woolly Bears will overwinter several years, getting a little further along each short summer, before finally pupating. Correction: This behavior is true for the closely related Arctic Woolly Bear (Gynaephora groenlandica). Though the Isabella Tiger moth is also found in the arctic, I have not found primary research data to support a multi-year larval lifestyle for our black-and-orange Woolly Bear.

!   It has hairs on its body but unlike many caterpillar hairs they do not inject a toxin, nor do they make you itchy when handled.

!   They move fast: 0.05 mph. At top speed, the Woolly Bear can cross a road in about 2 minutes. Just you try to keep in front of one bearing down on you to get an in-focus photo!

wb front
!    When they feel threatened, they curl up in a ball (actually, playing dead is not so rare an animal defense).
wb curled
Cool, huh? And that's besides just being so cute.

But here's something NOT true about the Woolly Bear, in spite of widespread belief. The amount of red and orange does NOT predict coming winter weather. That's folklore. Sometimes folklore has some basis in fact, but this one is completely unsubstantiated.

Professor David L. Wagner writes in his book, Caterpillars of Eastern North America, that various long-term studies by entomologists have averaged the width of many caterpillar's band each year and compared their measurements to the following winter weather conditions. What those studies have shown is that band size varies with the age of the caterpillar and the instar (molt) of the caterpillar, not with the upcoming weather.

As a Woolly Bear matures during its life cycle, it will cast off its old outer skin to grow a new one. A portion of the black bristles will be replaced by brown or orange bristles. After the last molt, usually towards the end of autumn or early winter, the brown or orange band is widest.  Thus, as the critter grows, the middle band expands. It's a natural occurrence with genetics, food sources,  and moisture levels in the area where it developed playing a role too. - nature documentary Frozen Planet. Series 1, episode 2, at around 26min 45sec.

On any given day in an area, you will find Woolly Bears with varying size orange bands because they are different aged caterpillars. Some grow faster than others.

Interestingly, a weather correlation that can be made is what the previous winter was like. A late winter means Woolly Bears thaw later, finish any larval development, pupate, become moths, mate, and lay eggs further along in spring than usual. The new Woolly Bears hatch out later, with less time to feed and grow. They will be less far along in their instars come fall, and have a smaller orange band. That small band doesn't mean the coming winter will be brutal, it means the previous winter may have been. However often the folk who like to believe in the myth will pay attention only to the years when the orange bands were small and the next winter was bad, ignoring other combinations of events. This a common fallacy in magical thinking: confirmation bias.

I followed a Woolly Bear recently after it raced across the road, and tried to get some photos of this icon of the season. Lying flat on the ground by the side of the road may have given some passing drivers pause to wonder what was wrong, but naturalists would have known. Here it is crawling over a stem. Cross country expert. And seen eye to eye, a bristly colorful alien creature with a face of shiny jaws.

wb climbing
This is what the adult moth looks like (from Wikimedia).
wb adult
Yay for Woolly Bears, which I've loved since childhood (haven't you?). Not spooky, but sweet and cuddly. It will be frost season here very soon, and then they'll all be tucked up safely in their hidey holes until spring. Until then, watch out for our Halloween-hued furry friends in the road please!

What are you seeing in your backyard as fall winds down? All observations are welcome in the Bucket.

and don't forget to check out -



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Originally posted to Backyard Science on Thu Oct 31, 2013 at 06:30 AM PDT.

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