Lisa and Pam talk with monarch researcher Tori Pocius to get the latest low-down on monarch butterflies: Their biology, life cycle, and migration.
Lisa and Pam talk with monarch researcher Tori Pocius to get the latest low-down on monarch butterflies: Their biology, life cycle, and migration.
Hello everyone and welcome to Pollinator Confidential, a podcast featuring the untold stories of native plants and the pollinators who love them.
Pam Ford:I'm Lisa Schneider and I'm Pam Ford, and we are Penn State Extension Master Gardeners from the Snetsinger Butterfly Garden Habitat Project located in Tudek Park in State College, PA. At the SBG, we're all about the stories, tales of those fascinating interactions between plants, pollinators and people, and many of the most popular stories revolve around monarch butterflies.
Lisa Schneider:We often call them the gateway insect, since people are so interested in their life cycle and migration, so it's especially appropriate that, for our very first podcast episode, we're talking to Tori Pocious. Tori is an insect ecologist who's worked with monarchs since 2009. She's worked with monarchs in five different states, with teams from New Jersey Audubon, Sweetbriar College, Monarch Watch at the University of Kansas, the Iowa Monarch Conservation Consortium at Iowa State and Penn State. She holds a master's in ecology and evolution from the University of Kansas and a PhD in ecology and evolution from Iowa State University, and she currently works as an industry entomologist and she has plenty of experience with monarchs and knows lots of good stories.
Pam Ford:And, best of all, we discovered Tori right here in our own backyard, or rather my front yard, since recently Tori moved just up the hill from me, so welcome Tori.
Tori Pocious:Thank you so much. I'm really excited to be here. No pressure, as your first guest.
Lisa Schneider:No pressure at all, none at all. So, Tori, when we spoke recently, you had so many interesting things to tell us. It's going to be hard to boil it all down and 30 minutes or less, but let's start with a monarch life cycle. So school children learn the basic egg, caterpillar, chrysalis, adult sequence but there's a lot more to it than that, right. For example, let's start with the egg. Most people know that milkweed is a host plant for monarch butterflies, but tell us more about that. How do the females find the plants and how do they choose the one they're going to lay their eggs?
Tori Pocious:That's a really great question. It's a little bit more complicated than you'd think and currently we don't have all the answers. All of the butterflies in the same family as monarchs actually have sensory organs on the end of their abdomen and in their feet. So a female will smell it, fly towards that plant and then use a visual cue. Sometimes it's leaf reflectance. It could also be color, because butterflies can see the entire UV spectrum.
Tori Pocious:So there are special markings on the flowers that give them an indication of what kind of plant it is and then as they land, they can scrape those leaves. They can really take in a lot of information about the plant using those sensory organs and decide good plant or bad plant, and then from there they may do more investigation couple leaves, take a little fly around the patch, check it out again and then, if it's good, they'll normally deposit one single egg on the underside of leaves, although in different places or based on the females experience, they may decide to lay a single egg on top of the leaf because that's easier for them. Why, I don't know. Maybe it's preference Drop and go.
Pam Ford:Drop and go. Well, we know that milkweed is toxic, but how do the caterpillars deal with that toxicity?
Tori Pocious:That's another great question and a little bit complicated it always is. So monarchs have a bunch of different adaptations that help them overcome the toxicity of milk weeds. Cardenalides are the main toxin in a milk weed, although there are other things in there as well. And what a cardenalide does? It acts as a cardiac glycoside which shuts down the sodium potassium pump across the membrane of insect cells. So if that's in balance, that cell's not doing so hot. They have an adaptation that enables them to work around that and actually sequester or kind of incorporate those cardenalides into their own bodies.
Tori Pocious:And it's interesting because there are a couple things going on there. Because it is a poison, there is a physiological cost of eating such kind of a quote nasty plant, because it's full of stuff you don't want to deal with and there are a lot of perils associated with that. So they will sequester a lot in the early portion of their lives. So those early end stars. But if you happen to be growing on a plant like butterfly milk weed, esglabias tuberosa, that does not have very many cardenalides, you can make up for that later on if you move to a different plant and really pack that in when you're a fifth end star as well, and you're kind of like that big, meaty caterpillar ready to go. So that's kind of interesting.
Tori Pocious:They have to process those costs. But as you're a caterpillar, there are other ways. You have to kind of avoid perils as well. Milkweeds have that kind of sticky white sap that comes out if you crack a leaf open. They also have leaf hairs, and so caterpillars will actually mow down the leaf hairs and strategically bite leaf veins so they can eat without being flooded by that kind of sap. A study done in the early 2000s actually estimated that up to 30% of early end star larvae perish because their mouths or their bodies are glued by that sap. And so you want to do everything you can trench those veins, get as far away from that stuff as possible. Then once they're older it doesn't really matter.
Lisa Schneider:So it's not just munch and go. They have to have a strategy.
Pam Ford:And you mentioned that they could move to another plant, so is that another reason we should plant our milkweed species together?
Tori Pocious:You can. That's interesting. Normally what they will do is they do not prefer to move from a low cardenolide species to a high cardenolide species, or because it's just harder for them to adjust. So that's not normally something that we'd see in the field, and often the milkweed species, those patches, are not close enough to actually see inner species movement. If they were, I would imagine they would move and then check it out and decide. I don't know if this was good.
Pam Ford:Not a good idea.
Tori Pocious:But they can try. They will switch food, but only if it's down that spectrum of toxicity instead of up in the lab. Gotcha.
Lisa Schneider:And do you mention that the childhood diet, or what the caterpillars eat as young instars, directly affects them as adults?
Tori Pocious:It does. I was very fortunate to work at Penn State with Dr Jared Ali and Dr Rud Schilder and that's exactly what we were looking at. So if you are a caterpillar and you have the option of eating eight different milkweed species, what does that actually do to you? In the field we still are not really sure, but we did see a direct correlation with the species and the amount of cardinolides ingested reflected in their adult metabolic rate at rest and both in flight. These were not migrants, they were breeding butterflies because we do not know how to make them migrants in the lab.
Tori Pocious:But that was a really clean first examination of there is kind of a residue of what you ate as a kid. So if you're eating broccoli and you're really powering your metabolism and you're chugging along and you're doing well, it's probably going to be a little bit easier for you. But if you decided, oh, I'm going to try to run a marathon on cheesecake, probably two thumbs down, there will be some kind of remnant of that choice, even though it wasn't your choice. Your mom left you there. But there is a cost. However, we know that from previous work that that larval diet can result in different body sizes adults or different larval lipid stores. So when that butterfly closes from its chrysalis before it eats at all, if you have fewer stores that may mean that you cannot go as far to forage on that first flight. But if you can successfully find a nectar source you can make up for that in no time at all. You're able to fully recover. You can be a healthy adult. Doesn't really matter.
Lisa Schneider:That's good to hear. Yeah, still, kids, don't eat junk, that's right. So most people are familiar with the monarch migration to and from Mexico, but the monarchs that we see here in Pennsylvania in early summer probably did not come straight from Mexico and they won't be returning there in September. So can you tell us a little bit about how the generations work?
Tori Pocious:Sure, I'd be happy to. So if we think of butterflies that we might be seeing right now, they may be starting to kind of do this pre-migration movement, but they're about normally the third or fourth summer generation of butterflies and what that means is that they're kind of the precursors to that migrant generation. So a lot of the eggs that were laid in mid-July that are now really close to becoming adult butterflies or are adult butterflies in Southern Canada and the Northern US, those are the migrants and they're starting to move. People are just starting to figure out what's that. There is some movement happening in Ontario. There are actually a couple reports that came out today. So the movement south is starting. But then that generation that starts that movement in Canada, those guys will go the whole way to Mexico. Other butterflies will join in along the way, whether they're from Pennsylvania or Iowa or Ohio or Texas, and they know it's time to go based on a variety of conditions that we haven't totally figured out yet. Some of them could be shorter day length, cooler overnight temperatures and decreasing quality of milkweed. So once they get that signal saying that it's time to go, they're on the move.
Tori Pocious:Those guys live for up to nine months. They go to Mexico. They are not going for margaritas, they are going actually to a natural refrigerator in the Trans-Volcanic Mountains and they are clinging for dear life to giant fir trees. So we think they go there because it's a perfect micro habitat for them. So it is, there is enough humidity. They don't dry out. It doesn't often freeze However, that has changed and there have been some dramatic freezes in the past few decades. But they're going down there and they're clinging.
Tori Pocious:They will feed on some nectar, they will drink some water. They might take off to stretch out their wings towards the end of that overwintering season. They'll fly up the mountain. They'll fly down the mountain, but most, most of the time, they're really clinging to trees, living off of lipid reserves that they built up on their flight south From there. Those butterflies will mate and they will leave those overwintering sites. They'll make it in a normal year to probably Texas, southern Oklahoma, and then their time is up. Then we're waiting for that first summer generation of butterflies to mature and they, then they will continue to move north. You have a couple more generations that continue to move north and east until they repopulate their entire breeding range east of the Rockies. Those summer generations will live most likely for six to eight weeks. Then that last generation again of the year will start that migratory cycle again. So it really is almost their grandchildren's grandchildren that are making that trip back. So you have multiple generations in between those migratory generations and they're physiologically different to the migrating generation.
Tori Pocious:They are. They have a couple of interesting differences. If you actually have wings side by side, the migrants are redder, they are larger, they have more wing area, so that front part of their wing is just a lot bigger to kind of help them glide on air current. South they kind of become like the Michelin man Pillsbury Doughboy. They can accumulate up to two and a half times their body mass in lipids which they store in their abdomen because they do not really eat when they're overwintering. So they'll really pack on those lipids in southern Texas, the northern Mexico and the final kind of interesting thing about that generation is that they're totally in reproductive arrest. So there's no mating, there's no reproductive tract development, there is nothing, unless they get too hot, but that's another story.
Tori Pocious:So we want to try and keep them a little cooler, make sure that that system doesn't get any cue to turn on, but they're putting all of their energy into really powering their flight instead of having two pathways open, in which one goes towards reproduction, making eggs, laying eggs, all that stuff. It is full speed ahead on. We got to get out of here. We have to fly south.
Pam Ford:No distractions and they're very focused feeders. The easiest monarchs for us to net for one more tagging are those migrating, because they are just focused on their journey, and we are what is called the eastern flyway. Is that right? So there's a smaller percentage of butterflies that actually make it to Mexico from this area?
Tori Pocious:Yes, so there are two major flyways east of the Rockies. The main flyway is the central flyway, where you know you see people talking about thousands and thousands of butterflies flying over their house and coming into their town in Texas, which is absolutely amazing. So the bulk of the butterflies that we see and where tags are recovered is coming straight down the middle of the country, from Canada, through Texas, down into Mexico Straight path, no ocean interference, pretty straightforward wind pattern most of the time, and they are really on a mission to get south. The eastern flyway runs along the Atlantic coast. It's interesting. Depends on where you are on the coast what your chances are of being recovered in Mexico, based on data from Monarch Watch, from tagging data. If you're in Cape Main, new Jersey, it's about a one in 10,000 chance that your tag is going to be recovered in Mexico. If you're a little bit farther south, in Virginia, it's about one in 2000. From Charleston, south Carolina, about one in 4,000. Whereas the average overall is about one in 100.
Tori Pocious:So, it's a big difference and we're not entirely sure yet what causes those recoveries to be so dramatically lower. But a lot of the hypotheses that have been discussed are interference with wind patterns or storms. And they don't really like to fly into wind. They'll have to fight. So they'd rather wait it out until there's a favorable wind than fly into a headwind directly. So I think personally, a lot of it has to do with the weather patterns on the east coast and we're not sure it happens to them exactly when they try to cut over the Gulf of Mexico. There have been very few reports of butterflies roosting on oil rigs, stuff like that, but very difficult to study. So I mean it's kind of these one off observations.
Pam Ford:So we know that they go out there but we're not really sure what happens next which makes it all the more amazing that two monarchs that we tagged at the Snutsinger butterfly garden were recovered in Mexico. So that's Considering those statistics, that's, that's pretty that's a pretty good average, yeah, yeah.
Lisa Schneider:So, and what does it mean to recover a tagged monarch?
Tori Pocious:That's another great question. I'm tagging is One of the best tools that we have to understand from a science perspective what's going on and what paths they may take, because we have great folks that are really excited about monarchs that go out and use those little stickers that are about the size of a pencil eraser with a special unique code and Also an email and a phone number to call KU. If your tag is recovered and A lot of the observations that we would receive were actually from birders looking for birds and they find a butterfly with a weird sticker and we get the call in saying we saw this butterfly here. If you're lucky, it's not from down the street but rather from somewhere else. So we kind of have some gauge of where they are.
Tori Pocious:In Mexico the tags are normally recovered from the forest floor or off of the wings of butterflies that have been consumed by rodents or birds that also need to eat down in Mexico. So oftentimes it's great proof that your butterfly made it to Mexico. However, it did not make it out, but that's okay. That gives us a really strong understanding of a recovery rate over time with a direct comparison of how many butterflies are tagged. So it kind of helps us understand mortality in specific years and Gives a really nice view over time of how those overwintering populations are doing so fascinating.
Lisa Schneider:Many people are aware of the plight of the monarch and they want to help, and there's been a lot of controversy over the Recent years about hand-rearing butterflies and whether it's helpful or harmful. What are your thoughts about that?
Tori Pocious:So I mean, first of all, as a scientist that has worked with a really charismatic insect for over a decade. It's really Wonderful that people are so excited and want to help, because that passion is a large reason why the monarch was precluded from listing on the endangered species act the first time around, because there was such a ground swell of efforts to help them that the agency did not think that Listing was required at that time. I do not believe they've made a final decision yet. I think we're still on the list, potentially this year, next year. However, the migration has been listed as an endangered phenomenon through IUCN for quite a while. It's kind of a double-edged sword because when you want to help any any way, you possibly can.
Tori Pocious:Personally, if you would like to bring in 30 or fewer caterpillars from your yard, from your garden, and use them as an example of Metamorphosis or that bugs are cool or pollinators are important in your community, I am in full support of that. However, I would highly recommend not bringing in every caterpillar that you see, or bringing in hundreds and hundreds, or making sure hundreds and hundreds over Multiple generations in the same container. So I'd really kind of try to put a cap on that enthusiasm. We have a limited number of monarchs. For a reason, not all of them are gonna make it.
Tori Pocious:Most about 90% of eggs are predated in their first night by spiders, by ants, by you name it. If it sees an egg, it's probably gonna eat it. That's how nature works. Everything has to eat. If you are going to bring monarchs into your house, please make sure that you're either switching containers after each caterpillar or that you are sterilizing with a 10% bleach solution to prevent disease from carrying on in your containers. What we really don't like to see is that folks are bringing Butterflies in and they're really excited and their caterpillars don't make it because they're infected with a disease that was left over in their container. So please be careful and try to curb the enthusiasm a little bit, but really enjoy the outside.
Pam Ford:That's very valuable information I'm sure our listeners will pay heed to. So we know that climate change is affecting migration. For example, the recent newsletter from Monarch watch Regarding drought effects of nectar production. Can you expand on that a little?
Tori Pocious:Sure, I have kind of limited knowledge about what's going on with this cycle of drought, but I was working with Dr Lincoln Brower in 2011 when the last kind of apocalyptic drought in Texas took place, where Everyone was referring to Texas as a hundred miles of hell. They didn't really know if the butterflies were going to make it through. Everyone expected the ones that did to be in really poor condition and In some cases it was not the best. In others, if they were able to find nectar sources, they were actually totally fine. So if there are pockets of available nectar, they're going to make it and be just fine.
Tori Pocious:However, if there's those corridors and those pockets are very limited, that also does limit the number that are able to make it through. Some that were collected on ranches had only five milligrams of lipid, which is barely more than they have when they first closed as adults, without feeding at all. Others that were able to find nectar kind of in the middle of the state were at about 50. But the ones that did make it to Mexico were at their normal about 200 milligrams of lipid. So, again, if they were able to find nectar and kind of enough to store, they were totally fine. So I am cautiously optimistic that those butterflies that do find those resources will be okay.
Lisa Schneider:That's a nice positive point on that. I like that. And finally, people who are listening to this podcast are probably pretty interested in what they can do to help monarchs and pollinators in general, so can you direct us to any favorite resources or speak to some things that we can do?
Tori Pocious:to help. Sure, there are a lot of resources available online. If you're looking for a pollinator friendly plant list, I would send you either to a pollinator partnership, where you can just literally Google pollinator partnership. It'll come up. You can actually put your zip code in and they'll try to generate an appropriate list for your area. So you're not planning something invasive or that will die because it's too cold or too hot. The same thing with the Xerces Society. They've worked really diligently to create plant lists with specific milkweeds based on ecotype and eco regions across the country to really make sure that the plants that you're putting in your yard or on your farm or really wherever you're planting, are well suited to that area.
Tori Pocious:The best thing that you can do is to make sure that when you're planting, you're planting native milkweed species that are going to be good for your space. So, for example, in my yard it's mostly shady. Same thing with my parent's yard in Northeastern Pennsylvania very shady. A lot of the milkweeds really want to just be fully blasted with sun so they can bloom and be very happy. But swamp milkweed can tolerate some shade and will still bloom. So I would suggest, if you have kind of a shady, maybe a little bit more wet area. I would try to put that one in and see how you do. The other really important thing to consider is nectar availability throughout the whole season. So you want to have plants that start blooming in late April for those early bees that come out the whole way through the end of September, if you can, for migrating butterflies, hummingbirds, any bug that moves. Also for the bees to kind of help store up some nutrition over the winter.
Pam Ford:Well around here. The big sign for us is when the New England Aster and the Golden Rotter and Bloom monarchs are migrating.
Lisa Schneider:That's right, and those fall blooming plants are important fuel for the monarch's journey.
Pam Ford:And remember, as Chip Taylor always says, even a small change makes a positive impact.
Lisa Schneider:Thank, you for talking with us, tori. We've learned so much today, and for our listeners who feel inspired to take action, we'll include a list of resources in the transcript of this show, and remember to check out our website snetsingerbutterflygardenorg for plant pollinator and bird directories, sample pollinator garden plans and lots more. Follow us on Facebook for weekly educational posts and if there's something you'd like to learn more about on a future podcast, drop us a line. And please join us next time for more stories on Pollinator Confidential. Pollinator Partnership: Pollinator. org