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Butterflies by the ka-jillions!

Sightings—many sightings—of the California tortoiseshell butterfly


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"Hey, Jim, this is Linda Sears. I'm on the road over to the Valley and from the Hoodoo summit to Belknap Springs there are thousands of orange and black butterflies everywhere! What are they and what's going on?"

My wife, Sue, listening to the conversation at her computer quickly said, "Oh, boy! It's another outbreak of California tortoiseshell butterflies!" And so it is!

I believe the current movement of the tortoiseshell butterflies (Nymphalis californica) is not a "migration" as some have remarked, but an "outbreak" linked to population dynamics of some kind or another not thoroughly understood.

About 30 years ago, an outbreak similar to this one took place in Northern California and was seen all the way to Bend. Unless research is carried out annually, it's probably difficult to really put your finger on this or that cause. But no matter; it's astonishing when it takes place.

Saying that, I also believe this remarkable phenomena is tied to nature's way of ensuring survival of a species. When weather and food plants are in balance, the butterfly's larvae get what they need to develop the necessary chemicals to successfully metamorphose into adults then mate and lay prodigious numbers of eggs, which in turn hatch—and because of the sheer numbers—defoliate their food plants, which I have a hunch is even good for the plants in some way.  

In addition, while this is going on, butterfly parasites also go into supercharge mode and somehow have the ability to lay eggs on the ka-jillions of caterpillars. During the event some 30 years ago, my wife and I were living in Bend, having just returned from Arizona where I was manager of the Ramsey Canyon Preserve.

During that outbreak of the mid-'80s, someone told us about seeing tortoiseshell butterflies all over the Tumalo Creek watershed. We packed up our son, Reuben, and went out to Tumalo Falls to take a look. It was astonishing to see that many butterflies filling the air, and to actually be able hear the larvae munching on ceanothus leaves as they defoliated all the bushes. 

What was also unbelievable when we returned a short time later was finding uncountable numbers of chrysalids hanging on the bare branches of the ceanothus. We then discovered (by accident) that if we got close to them and stomped our feet they would all begin to shake and clang like tiny bells. What a show!

We removed 20 chrysalids from the underside of the bare branches, using my pocket-knife to cut the thin, silk pedicle attaching the chrysalis to the branch, and took them home with us to photograph emerging butterflies. However, if my memory serves me correctly, of the 20 chrysalis, eight or nine developed butterflies; bright green parasitic wasps emerged from all the others.

Another facet of an outbreak of this nature is it provides the species enough adult insects in summer to travel far from the "breeding territory" and pioneer new habitat, further increasing the chances of the species to succeed.

During the outbreak of some 30 years back I also recall the California Department of Transportation installing special truck washing equipment near Redding, used to wash smashed butterflies out of the radiators to keep trucks from overheating. UPS drivers were also having a heck of a time, driving five miles, then having to stop and clean the windshields of their trucks.

The Oregon Birders Online website has been buzzing for weeks with birders sharing the tortoiseshell outbreak, and this one from Barbara and Dan Gleason of Eugene was particularly thoughtful as well as interesting:

"Seeing all the posts, I thought I'd add that these massive numbers of butterflies were also in the Clear Lake and McKenzie River areas, too, this past Thursday."

"My granddaughter and I were up there for her first rowboat ride and everywhere we encountered massive numbers of tortoiseshells, to the point it made driving quite hazardous since one couldn't help but want to avoid killing them, but one could not drive as slowly as one need to accomplish this.

"We were glad to get off the highway and head to the lake where one could drive to allow them to pass by the car. They were largely not over the lake but were everywhere along the roadsides, especially near water...culverts, outhouses, included!

"Along the edge of the lake when one moved too quickly, they would all take flight and one could hear their wingbeats.

One of the reasons I've enjoyed writing this column at the Source all these years are the phone calls like Linda's, and emails that come in and alert me to some natural history phenomena taking place somewhere I ain't. This time it was another astounding outbreak of California tortoiseshell butterflies taking place from the crest of the Cascades all the way to Bend and beyond. Indeed, it's a sight to behold when Mother Nature decides to put on a rare show like this one; aren't we thankful we're alive and live where we do.

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