Pandora Moth Invasion

I caught the tail end of the Pandora moth outbreak on a recent visit to Bend, Oregon. I lived in Bend for almost five years without seeing a single Pandora moth. This summer I saw thousands littering the streets and parking lots, mostly dead or dying. When I asked friends about the moths, I got shrugs. Nobody really knew what they were or where they came from.  I was fascinated. Was this a foreign invader, a ravenous beast that would defoliate the state? Would its larvae overwhelm the town come spring?

Transcription:

Dustin Driver:
The moths streamed out of the forest, a fluffy brown cloud of soft, chalky wing beats and long twitching antennae. They float through the towns of central Oregon like thick fog, smothering street lights, clogging ventilation systems, and blanketing sidewalks. The moths were everywhere.

Rob Flowers:
Perhaps one of the famous stories was at the Bend Elks Stadium, which is our local baseball team. With all the outdoor lights at night, they had these huge amounts of moths that descended on the baseball stadium, and they lighted on all of the foul ball nets. So, every time a ball would hit the net, hundreds of moths would go flying off the net. Some would go into the crowd, some would go onto the field, and there’s players swatting at them, there’s fans swatting at them. It was this When Cultures Collide, when the natural world breaks into our normal, everyday life in the summer, so it was interesting to be there and see the public response at having these hundreds of moths that are landing in their beers, landing in their nachos, and things like that at the stadium.

Rob Flowers:
Then, at the end of the night, the staff would take leaf blowers and go through and blow all the moths off of the sidewalk, because there were just so, so many. It really was this situation of the natural world crashing into our everyday life.

Bend Elks General Manager Michael Hirka uses a leaf blower to clear out Pandora moths from a walkway at Vince Genna Stadium on Thursday in Bend. (Joe Kline/Bulletin photo) ©

Dustin Driver:
After a few days, the moths began to die off. Their corpses were everywhere.

Jen Lande G.:
This Jen Lande Galewski. There were a lot of moths around, and mostly I saw them dead on the ground. I’ve been here eight years and I’ve never seen anything like that. They were really pretty, too, so it made me feel bad to see them dead everywhere, and would like to know the reason why.

Dustin Driver:
I caught the tail end of the pandora moth outbreak on a recent visit to Bend, Oregon. I lived in Bend for almost five years without seeing a single pandora moth. This summer I saw thousands littering the streets and parking lots, mostly dead or dying. When I asked friends about the moths, I got shrugs. Nobody really knew what they were or where they came from. I was fascinated. Was this a foreign invader, a ravenous beast that would defoliate the state? Would its larvae overwhelm the town come spring?

Dustin Driver:
Turns out the pandora moth is a native and the outbreak is totally normal. The moths are always around, but every 8-10 years they have a tremendous population explosion. The furry moths swarm the forest for a few years then return to normal population levels. I wanted to know more about the moth and why there were so many of them in Bend this summer, so I called Rob Flowers, an entomologist with the National Forest Service. He lives in Bend and saw the outbreak firsthand. That was Rob describing the infamous moth invasion at the Bend baseball stadium. We spoke via phone about the moth, the recent outbreak, and what it means for the forests of central Oregon. Turns out the moth isn’t really a plague after all, and is one of the more interesting insects in the mountain regions of the US. Plus, they’re really freaking cute.

Rob Flowers:
The pandora moth is one of our largest native moths, and they have a wingspan of about 2 1/2 to 4 inches. The moths are generally grayish-brown, but they have these really beautiful, rose-colored hind wings, and they’re also very hairy. The larvae, usually they start off with shiny black heads and brown or black bodies with a few short, dark hairs. But then, by the time they finish developing, they’re usually up to two inches, about the size of a double A battery, and usually yellowish-green in color with stout, branched spines on their bodies.

Dustin Driver:
Pandora population explosions are pretty infrequent, which is why you can live in central Oregon for than a decade without seeing one.

Rob Flowers:
Well, with most of our forest insects, they don’t typically go into these outbreak-size populations. Usually, they exist along this continuum of just having a few insects out in the forest to having millions of these insects in the forest, in terms of pandora moths. Typically, what happens is there’s this slow buildup over about six to eight years. So, the first year, back in around 2015, we first starting noticing some moths. Then we found some larvae in 2016. Again, they were kind of at low levels, almost to the point where the public wouldn’t perceive those.

Rob Flowers:
Then, as we moved into 2016-17, there was these increasing populations that people began to encounter them a bit more commonly. They tend to be really attracted to lights at night, so if you have exterior lights on your home, you would see these moths showing up. If you were out biking or hiking in the forest, you may see these larvae climbing down from the trees and going into the soils, so we started getting a lot of questions about those.

Rob Flowers:
Then, really 2018-2019 was really our big year of the population explosion. What that looked like in terms of the larvae is they were fairly heavy defoliation over about 145,000 acres, is what we estimate it at in central Oregon. So, this large-scale defoliation, they would eat all the needles off these trees. Usually, it’s ponderosa pine or lodgepole pine is their preferred food. We would see all these trees that that were stripped. People were driving down the highways and getting very concerned about what looked like dying trees that was the effect of these very hungry larvae consuming all that foliage.

Rob Flowers:
Then, those larvae became the adults that then… in 2019, we had this really large explosion of the population. What you typically see is st, say, a gas station at night, you would see thousands of these moths, all around the lights, on people’s cars. They were all over the place, to the point where we were getting calls from businesses and others in the community as far as what they could do to prevent these large numbers of moths descending on their lights at night. It became this really public concern because there were so many moths occupying these areas at night, around these businesses.

Dustin Driver:
So, how many moths are we talking about? It’s almost impossible to tell without an extensive forest surveillance network, but it’s probably safe to put their numbers in the millions.

Rob Flowers:
Yeah, we really don’t know. It’s something that would be incredibly hard to quantify because you do have all of them that are existing in forest environments that we’re not really perceiving on any regular basis. We’re really just seeing what comes into our urban community forest areas within and around our homes and places like that. We’re not really observing it on the whole, but I would estimate it would be in the millions or larger, in terms of the amount of defoliation that we saw in 2018 and the number of moths we saw this year.

Rob Flowers:
It was a really period this year, too. It seemed like there’s definitely environmental conditions that seem to interact with the life cycle. It definitely seemed like we had a very long amount of adult activity this year, just in terms of the number of calls I was receiving over that time.

Rob Flowers:
It’s really hard to quantify that. Our best estimates, as far as comparing now to historical, it usually winds up being… we do these forest health aerial surveys where we actually go around and try to document how much of the forest area was affected, so we can look back historically and see that these outbreaks have occurred in similar areas to a similar size that they’ve been, at least in the last several decades that we’ve been doing this.

Dustin Driver:
The long life cycle of the moth also makes it difficult to get an accurate count. They live for about two years, which is a long time for an insect. The caterpillars hatch in the spring, eat all summer, endure the freezing and snowing winter, then climb down out of the pine trees. They weave their cocoons among the rough volcanic rocks that litter the forest floor, and emerge in the summertime as full-grown moths. They party, then start laying eggs all over the place.

Rob Flowers:
Well, the life cycle, it usually consists of… For example, this summer when the moths are active, usually those adults are laying eggs in July and August. That can be on foliage, bark; sometimes it on the side of buildings or other structures. Typically, when it’s more of in a forest environment, the young larvae will hatch, usually in August or September, and then they’ll move up into the trees and begin feeding on the needles. Then, those larvae actually overwinter as larvae, so they’ll cluster together at the base of the needles to stay warm and ride out the winter. Periodically, they’ll resume feeding on warm days in the winter. At that stage, you usually don’t see the caterpillars. It’s pretty difficult to actually observe them.

Rob Flowers:
Then, in the following spring, in March-April of the next year, usually they’ll continue feeding into late June or early July. It’s usually the phase when the caterpillars finish feeding and they start moving down the trees into the soil. They actually burrow into the soil to pupate before they emerge as adults. That’s usually the period where most people will see them. In the soil they will transform into the adult moth, and then they will emerge and resume the cycle.

Rob Flowers:
In full, it takes about two years for them to complete their life cycle. There are some moths that have a two-year life cycle like this, others have an annual life cycle. It tends to be on the longer side, in terms of the development, relative to some of their closely-related species.

Dustin Driver:
The caterpillars eat a lot. The Forest Service estimates that they munch their way through 145,000 acres of pine forest, but the trees can take it.

Rob Flowers:
It’s advantageous for the trees as well because, if you’re a tree growing in the forest and you’re going to have your needles eaten off, it’s advantageous to have a year of growing in between. So, you don’t get this annual defoliation, it’s this every-other-year defoliation that occurs. We usually see that trees are able to survive these type of outbreaks better than, perhaps, with some other defoliating insects because they do get that year off of pressure from the defoliation. So, they can continue to grow and be free of the insects for one year before they’re faced with that again.

Dustin Driver:
In fact, there’s a long history of moth outbreaks in the region, both written on paper and in the tree rings.

Rob Flowers:
We have a long history of these insects. The first recorded outbreak was in the 1890s; it was in some tribal lands in Klamath County. We have documentation going back that far, as far as recorded history, and then we can look at the tree rings and we can actually date these things back hundreds of years. Through tree ring analysis, you can actually detect periods of defoliation versus other types of stress in the tress from drought or from other types of fire and other injury. We can actually backdate this for hundreds of years by looking at some of these really old ponderosa pine in the area, so we know that we have this long history and association of this insect in central Oregon.

Dustin Driver:
Pandora outbreaks typically last for eight to six years before the population collapse. 

Rob Flowers:
On the tail end of these outbreaks, we do see a lot of activity from their normal, natural enemies. There’s a number of predators, there’s both mammal predators, there’s insect predators. There’s insect parasites, as well, that will increase their populations as the populations of pandora moth rise. It does seem, with a lot of the caterpillars, it’s really these diseases that control or end the outbreaks. Usually, what happens is, it’s almost… you could think about it terms of the flu, if you have a lot more insects out there that are able to contact each other, it’s easier to pass around these viruses. So, it’s usually a larval-to-larval spread of the virus that happens. Then, that can very quickly move through a population and cause the collapse of that population.

Rob Flowers:
This is a naturally-occurring virus that is in the population, but it really doesn’t get expressed, in terms of doing a lot of damage, until you get a large population of insects that are encountering each other. As they continue to interact and spread the virus around, you usually go through this really rapid decline of the population; it almost just disappears in a single year. So, it’s as much of a mystery on the front end and the initiation as it is on the tail end when we just see these things collapse. Typically, it seems that the time period for that to occur takes in that six- to eight-year window of time, is really the amount of time it takes for that cycle to play out, of rise-peak-fall. But yeah, it’s really those diseases that move through the populations very quickly that tend to bring about the end of the outbreaks.

Dustin Driver:
But while the moths are around, they’re an important food source for the animals and, in the past, the people who live in the forest. The tribes who once lived throughout the forests of central Oregon used to harvest pandora moth caterpillars. They made a kind of grub jerky out of them, and used them in stews throughout the harsh winters.

Rob Flowers:
Yes, we actually do have this history of the tribes that occupied the high desert using pandora moths as a food source. They would typically collect the larvae, usually when the larvae are moving down from the trees they move down into the soil, so it’d be fairly easy to collect. They would take all these larvae and they would actually fire roast them in the soil pit, so that you could burn all the hairs off; you wouldn’t want to try to eat these spines and hairs that are on the larvae. That would preserve them in such a way that they could basically have them as a snack, as a caterpillar jerky, for lack of a better word. They could certainly use those during the winter whenever there was less food available.

Rob Flowers:
I’ve read stories about the preparation in terms of… that they would use the in stews and soups, and other things like that. Basically rehydrate these in the winter as a protein, carbohydrate food source that was readily available because you could collect them in large numbers. I’ve actually asked several tribal members that I’ve encountered over the years, if this is still a normal practice, and I haven’t really run across that this is something that they still do as part of preserving tribal cultures. But I would really like to find out what the exact procedures and recipes are for these things. I think it would be really interesting, in light of a lot of other cultures around the world currently use insects for various types of food supplements and otherwise.

Rob Flowers:
I’ve not personally tried these before, so I can’t really testify as to how tasty they are, but I would assume that this was more a product of really having a limited food environment; you’re really trying to gather and collect as much as you could to survive the winter. But with that said, it would be interesting to see what it would actually taste like.

Dustin Driver:
Pandora moth outbreaks are fascinating natural events, and part of the unique and complex American ecosystem. Sure, it’s a pain to clean up after them, but it’s a spectacle to behold.

Rob Flowers:
We’re part of this dance that’s happened for hundreds, thousands of years here, in our area, and we just happen to be in the middle of it right now. Look at it more as like I have this opportunity to witness this incredible natural event rather than really focusing on the fact that I have moths all over my front porch.

Dustin Driver:
So, what about the name “pandora moth”? It was first describe by entomologist C. A. Blake in 1863 in the Proceedings of the Entomological Society of Philadelphia. He wrote a detailed description of the moth, including its name, but didn’t mention who gave it the name to begin with. It’s a pretty safe bet that it got the name pandora after the first outbreak was observed by a westerner. Pandora was the first human woman, according to Greek mythology. She opened up a jar, not a box, that was a mistranslation, and unleashed evil upon the world. Of course, the pandora moth wasn’t evil, but the population explosion probably seemed like something of a myth to early western travelers.

Dustin Driver:
Nowadays, the story of Pandora is considered to be pretty misogynistic. I mean, it totally reads like it was written by Pandora’s disgruntled ex-boyfriend. But I digress.

Dustin Driver:
Pandora moths aren’t a threat to central Oregon forests by themselves, but they could contribute to a rapidly worsening situation. It’s getting hotter and drying, which stresses the trees. If the trees are already stressed from a dry summer, a pandora outbreak could do some harm. But really, the most danger to the forest comes from hotter, dryer summers and poor forest management. We’ve been suppressing forest fires for a long time and, as a result, there’s a lot flammable undergrowth that could flare up.

Rob Flowers:
One way to look at it would be that it’s just a very normal, natural cycle. The trees that are existing in forest environments, when they are defoliated like this, they tend to recover because they do have that year off as the life cycle continues, and you only get that one year of defoliation and they get a chance to grow again. But we’ve looked at it, at least in terms of some of the work they’ve done historically, they haven’t really found a lot of mortality in trees. A lot of these trees that get defoliated, they bounce back and they survive. We don’t often see them dying, except in cases of really severe droughts or in cases where you have ongoing bark beetle epidemics. Those insects can basically take advantage of the fact that these trees are in a weakened condition, they can go in and kill some of those trees.

Rob Flowers:
We see that the amount of mortality that occurs now, at least what we’re observing, has been consistent with what we’ve had historically. So, we aren’t really concerned about losing lots of trees to these native insect cycles, but what is concerning is as far as what the future may hold, especially as it relates to climate and environmental stress in central Oregon. What a lot of the climate models would suggest is that we’re going to have these warmer, wetter winters, and then we’re going to have these hotter, dryer summers. Overall, you have a net drying effect, you have these prolonged drought cycles, are one of the expectations, and more severe drought stress and heat stress on these trees.

Rob Flowers:
These trees are also growing in an environment where we’ve suppressed fire for a very long time, so you have higher densities in these forests, you have species compositions, trees that normally would not be there because they would have been excluded by fire are there now. The stress associated with the combination of those things is something that we do worry about in the future, in terms of actually seeing a lot more tree mortality related to these type of event.

Rob Flowers:
That’s really an unknown at this point, but a lot of our efforts are, at least on the Forest Service side of things, on National Forest science, is trying to restore those forests back to more of their historic condition, to be able to allow them to be more resilient to these type of events when they occur. It does create a very short-term stress situation that we would hope most trees would be able to survive, but certainly as you get the compounding of these factors, you have the insects, plus you have more fires, plus you have drought conditions, we may actually see a lot of increase in terms of the extent and the duration of the mortality events in terms of trees dying.

Dustin Driver:
Luckily, helping to prevent forest fires is something pretty much anyone who lives near a forest can do. First and most obviously, don’t have campfires or play with fireworks in the woods in the summer or fall. In fact, don’t play with fireworks anywhere in the woods at any time of the year. In double fact, just don’t play with fireworks. Also, you can volunteer to help the Forest Service maintain the forests and prevent forest fires.

Rob Flowers:
Public involvement is really key. As resource professionals, we have a very limited ability to do, a lot of times, these larger-scale projects, so you really need to try to approach thing from a landscape level. One of our real, key phrases now is “All lands,” thinking about National Forest lands as well as the state and private lands that are next to them, and trying to enact the work that we do over all those landscapes.

Rob Flowers:
We do have a lot of volunteer opportunities. You can jump in on a citizen science capacity or in terms of doing some of the other work and maintenance activities we have in the forest, or helping with educational exhibits and other things like that. So, discoveryourforest.org is our main arm of being able to really provide people opportunities to be able to step in to a forest environment and be able to help; something they can do locally, in their own backyard, to be able to… at least encourage them to be more engaged, and to help preserve forests for future generations. It’s something that we, ourselves, have very limited capacity to be able to enact the types of change that we need, but when everyone is contributing and everyone’s jumping in on and assisting in those type of efforts, it certainly is extremely helpful and allows us to be able to accomplish a lot more.

Dustin Driver:
Again, that was discoveryourforest.org. Go visit the website and see how you can help out. Just a few hours of your time can make a big difference. Plus, you go get to hang out in nature with cool people like Rob Flowers.

Dustin Driver:
That’s it for this episode. Thanks for sticking around during my long summer absence. More cool stuff to come, including a podcast about the most metal alternative fuel ever, metal powder.

Dustin Driver:
You can subscribe to the podcast on Apple Podcasts or Google Play. If you like what you hear, give me a review. It really helps.

Dustin Driver:
You can learn more about me and read the transcripts of all the Let’s Get Mental podcasts on my website, dustindriver.com.

Dustin Driver:
Thanks again, and, as always, stay mental.

Rob Flowers:
There’s this public perception that we’ve figured everything out in terms of these really common, natural environmental events that happen, but the reality is there’s still a lot of mystery to it. Nature always surprises us. As a scientist, I enjoy that aspect of it, that we just never really know everything that we think we know. There’s always something new and interesting that emerges that surprises you.

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