LEPS & ODES: A banner year for monarchs
Websites for tech-saavy readers
• Monarch Larva Monitoring Project (mlmp.org): See results for 2018 season, also how to participate in 2019.
• Monarch Joint Venture (monarchjointventure.org): An information clearinghouse that answers general questions about monarchs and their conservation.
• Journey North (journeynorth.org): Updated with two-week interval maps showing where migratory monarchs have reached on their way to Mexico.
• Monarch Watch (monarchwatch.org): A monarch tagging program. All tags for 2018 have been distributed. Details available for 2019 season.
You can certainly believe your eyes if you thought you saw the most adult monarchs this summer in years. I have collected data that prove it was not a figment of your imagination.
Originally, I intended to write this column a few weeks ago. Happily, the 2018 monarch season, like the Energizer Bunny, has kept going...and going.
Here, I'll mostly focus on the 21 years that Marlene and I have been doing weekly monarch monitoring. We've been doing it under the auspices of the University of Minnesota's Monarch Larva Monitoring Project (MLMP).
Our weekly visits over those decades have been to Alan and Kathy Olander's "Wolf Song" property in Akeley Township. Alan has accompanied us when his schedule has allowed.
When we began in 1998, MLMP was in its infancy, only a couple of years old. We chose six sites with common milkweed present. Our 14 weekly visits tallied only nine eggs and 19 caterpillars. Yes, that was a discouraging start given the quite a bit of effort we expended.
However, we did persist. For the 20 years spanning 1999 through 2018, we've paid 317 visits to three sites there each week. We've checked 99,873 common milkweed. We've found 4,170 eggs and 2,065 caterpillars on those plants. Additionally, 489 adult monarchs have been present at the sites themselves at the times of our visits.
What we've learned
In just a few words and numbers, it's tough to characterize the ups and downs of monarch activity we've witnessed. But here goes:
• 2018 mixed bag: In keeping with the theme of abundant adult monarchs in 2018, we had 54 at the sites this summer. That was the most since 50 in 2007. However, the three sites produced only 92 eggs and 53 caterpillars this summer. That was a far cry from the 570 eggs and 368 caterpillars in 2007. Though adults were noticeably up, the eggs and caterpillars per 100 plants were both noticeably down from our 19-year average at Wolf Song. That suggests to me that many of the adults were not locally produced, but rather to the north of the corn-soybean belt. (I will readily concede I have no proof one way or the other, but something to ponder.)
• Too many eggs in one "basket": Normally, monarchs lay one egg per plant. With climate change getting things out of synch, there are now years when egg-laying females arrive before many milkweed have emerged locally. This was the case, I feel, in 2003, 2005, 2006, 2007, 2010 and 2012.
How do we know? A) By the number of plants with three or more eggs each, not the normal one. (Very infrequently we find two eggs on a plant.) In that regard, 2012 went from the sublime to the ridiculous with one plant covered with 20 eggs! In 2012, 36 percent of the plants with eggs had only one each. In sharp contrast, 2018 was more "normal" with 90 percent of the plants having eggs had only one each. That was certainly a big plus for any "success" monarchs may have enjoyed here this year!
• Consequences: What happens if there are too many eggs on a plant? Marlene and I have returned the following week to find no eggs nor caterpillars on the multi-egg plants. Why? We feel the multi-egg plants served as "all-you-can-eat buffets" for birds, ants, spiders and so forth. That's just the opposite of "strength in numbers!"
As you probably know, monarch caterpillars "have" to feed on milkweed. That's because the monarchs sequester cardenolides from the leaves that make them "toxic" (at least disagreeable to predators). Obviously, the eggs themselves don't benefit. Our multi-decade observations cause us to feel that first and second instar caterpillars generally have not had a chance to ingest enough. That leaves it up to the later third, fourth and final fifth instars to become increasingly more toxic as they munch away. Even after 21 years and 331 weekly monarch monitoring visits, Marlene and I readily admit there is much more to learn. We certainly plan to continue our monitoring saga.
Broadening monarch focus
So far, I've only mentioned our MLMP effort. Now I'll branch out to monarchs on our butterfly counts and the adults I've observed on my walks.
• Eight butterfly counts in 2017 and 2018: We had an average of one adult monarch per 20 minutes in 2017; one for every 6.5 minutes this year. Though the party-hour effort was similar for both years that was a startling three-fold increase this year.
• Monarchs while walking: In 1995, I started keeping track of all butterflies on my walks. The 1,569 adult monarchs I saw in 2015 were the most I'd witnessed in a single year. So far, 2018 is on pace to exceed that number — just another indicator of what an exceptional monarch year 2018 is shaping up to be.
A bold prediction
In 2015, the already-mentioned 1,569 adults on my walks were 4.4 times more than I had in 2014 (i.e. 358). Overwintering monarchs in Mexico in 2015-16 occupied 3.5 times greater number of hectares than the 2014-15 winter. Did "my" monarchs contribute to that significant uptick? (I can only hope!)
With 2018 on pace to meet or exceed my total for 2015, I'm predicting an increase in over-wintering hectares for 2018-19. Applying 3.5-fold increase to the 2.48 hectares occupied in 2017-18 would yield 8.68 hectares for 2018-19 winter. That would be the greatest area since 9.36 hectares was reported for 2001-2 winter.
In early September, local phenologist Dallas Hudson posted on Facebook that it was the "best monarch year in 25 years."
However, I'm tempering my prediction to 5.0 hectares. That would still be the greatest area occupied in 10 years! No small feat given the many challenges monarchs face. To get to Mexico, they will be finding fewer nectar sources due to agricultural practices and excessive roadside mowing, plus crazy weather producing high winds and floods.
"Proof is in the pudding" as the saying goes. We'll just have to wait in suspense on my prediction until the overwintering data for 2018-19 are released next March. Stay tuned.