The Great Monarch Migration

In mere weeks, a humble insect will begin an incredible journey. The current generation of monarch caterpillars, Danaus plexippus, is preparing to transform and make their annual migration. The butterflies take to the wind as the end of summer draws close, bound for warmer weather in Mexico. Most of the monarchs born in our stretch of the Blue Ridge will depart by mid October, though we may continue to see populations from further north passing through until the first frost. Once in Mexico, hundreds of millions of individuals crowd flowers and hang from trees in enormous roosts- also called bivouacs- while they wait out the winter weather. 

Some of the butterflies in our collection. The three in the bottom left box are monarchs, Danaus plexippus. The middle butterfly is a male, evidenced by the pheromone-producing black spots on the vein of the hind wing called his “pouches.” The top and bottom are females, who tend to have thicker black lines along the hind wing veins and lack these pouches. The box above them holds three commonly confused, but still very cool, Viceroy butterflies- Limenitis archippus. They mimic the coloration of monarchs and are similarly distasteful to predators. Notice the continuous black arc on the hind wing that runs parallel to the wing border present only on viceroy wings.

A female monarch visiting milkweed in our rain garden, likely selecting a suitable plant to host one of her young

When temperatures start to rise and days grow longer in northern Mexico, the monarchs prepare to make their return flight by increasing nectar consumption and beginning to mate. Come March, the butterflies depart- following the spring warmth as it stretches north. On their return flight, the butterflies fly low and stop often to feed and lay eggs. A female monarch may carry more than 300 fertile eggs at a time, and will continue finding new mates as she journeys onward. Mother monarchs are very particular about where they will leave these eggs. While the adult butterflies forage nectar from a variety of flowers, the caterpillars exclusively feed on milkweed species. She carefully examines each milkweed plant she finds and, should it pass her inspection, lays a single egg on the underside of a leaf near the top of the plant. This ensures her caterpillars have plenty of food to grow quickly without competing with others or decimating the plant. 

Monarch caterpillars feed exclusively on milkweed- a plant that is toxic to many other animals. The monarch stores these toxins in its own body so predators learn not to eat them.

Many of you are aware of the monarch butterfly migration; and we all are familiar with the four stages of their complete metamorphosis from egg to caterpillar, then chrysalis and finally adult butterfly.  However, the way these two life cycles interact may come as a surprise. In our region, D. plexippus experiences 4 generations every year. We have two generations of summer monarchs composed of small, short-lived individuals who will only know this land as home. The successors of the second summer monarchs are significantly larger, stronger, and longer-lived (Up to 9 months as a butterfly!) It is this generation, the fall monarchs, that will make the entire flight to Mexico and return more than halfway back, dispersing their eggs the entire return flight. From these eggs emerge the spring generation, who will complete the migration past the US’s northern border, recolonizing their entire native range.

Poster created by Paul Mirocha for Monarch Watch. This stylized map shows the seasonal ranges of monarch migration over North America. Our fall monarchs fly to Mexico before winter, then fly up into the South East in the spring. The next generation continues moving north, recolonizing the northern half of the continent. Summer generations breed in the north until the rise of the next fall generation, who will make the entire migration south to Mexico and halfway back.

Despite being one of the most extensively studied butterfly species, there are still many mysteries entomologists are working to solve. A community science project called Monarch Watch has volunteer participants help generate data about monarch populations during the fall migration. Unfortunately, the winter roosts in Mexico have been rapidly shrinking in recent decades, sparking much of the research and conservation efforts going on now. Leading theories of causes for this decline include habitat loss and resource scarcity. Much of their historic breeding and feeding lands have been converted to farms, making the butterflies’ journey even more perilous.

Monarch Watch is a community science project that began in 1992. Participants catch and tag fall migrating monarchs with a sticker that has a unique code. Data is recorded including the tag code, date, location, and information about the individual, before it is released. In the winter, butterflies are recaptured in Mexico and searched for tags. The data generated is crucial for estimating monarch population change over time as well as predicting migration times, routes, and survival rates.

Helping monarch populations can be an easy feat for anyone with the lawn space to grow a few native plants. Research some local long-blooming wildflowers, especially those that provide plenty of nectar and bloom through fall. Asters, columbine, vervain, mountain mint, and many others are fairly low maintenance native wildflowers that are great nectar sources for pollinators, including monarchs. Milkweed prefers to have a fair amount of space and well drained soil that gets plenty of water. However, there are several varieties that prefer different conditions, so researching a variety that would do well in your area is a great way to support the monarch population.

At our latitude of around 36° 50’ N, monarch tagging begins at the end of the month- August 29. Peak abundance usually occurs in late September, and the last of this year’s monarchs might be seen into early November. As we look forward to watching another generation of butterflies follow in the wingbeats of their great-grandparents, let these beautiful creatures remind you of the enormous cycles that make up nature.

Happy Bee-lated World Bee Day

We all love bees for the enormous role they play as pollinators. Over a third of the food we eat is thanks to these incredibly hard workers, as well as nearly all flowers and even many trees. When most people hear about bees, they usually imagine the European Honeybee, Apis mellifera. While this is an extremely important species to us humans, they are far from the only important species of bee out there. In fact, over 20,000 other species of bees have been described! Here in the US, more than 750 species can be found east of the Mississippi River. About a quarter of our native bees are specialists, meaning they have coevolved with a specific host plant to feed from and transfer pollen between its flowers. Without these native bees, a huge diversity of native wildflowers would disappear.

This Dunning’s Miner, Andrena dunningi, is taking a quick rest on a guide’s hand. As their name suggests, mining bees are ground-nesters. Females dig narrow burrows, preferably in clay soil. Although they are solitary nesters, several females will often construct nests near one another. These small bees overwinter as adults in their brood cells and emerge in early spring. While many mining bees are specialists, the Dunning’s miner is happy to visit several different families of spring blooms.

Despite being the poster child of Apoidea (the bee family), the European Honeybee is actually not very representative of the rest of the bees. While a few other species have social nests (the bumble bees and a handful of sweat bees), the majority of our native bees construct solitary nests or even just a few dispersed brood cells without a nest at all. Even in these social nests, there may be several fertile females that work together to raise their young rather than a single queen. Most bees nest underground, in plant stems, or in tree cavities and pack brood cells with enough rations to feed a larva to adulthood. The female will then lay a single egg in each and seal it off. These species are usually univoltine, meaning they have one generation every year. The larvae only eat the provisions their mothers stored for them before they pupate and emerge as adults the next year

The Spine-Shouldered Cellophane Bee, Colletes simulans, is a Goldenrod specialist. Like the rest of the Cellophane Bees, they nest underground in dry, sandy soil. This group of bees get their name from a plastic-like wax the females secrete that they use to line their nest, holding up the walls and making them waterproof.

There are many important pollinator species- butterflies and moths, flies, beetles, even some birds and bats. All of these species visit flowers to drink from its nectar and sometimes graze on pollen, then “accidentally” transport pollen between flowers. Bees are unique in their behavior of collecting and moving pollen on purpose. Female bees collect large quantities of protein-rich pollen and carbohydrate-rich nectar to provision her brood cells. As she visits flowers, she collects pollen in her pollen basket, commonly found either on the hind legs or under the abdomen. Upon visiting a new flower, she drops off some pollen she is already carrying to make room to pick up more. This results in very high rates of pollen exchange, helping the plant successfully fertilize its seeds.

This Two-spotted Bumblebee, Bombus bimaculatus, is collecting pollen from a sneezeweed aster. Perhaps the best known group of native bee, the bumblebees are adept pollinators. Most species are generalists and are active the entire growing season. Thanks to their long proboscis and robust build, they are able to access flowers with concealed nectaries. They are also some of the only native bees that live in eusocial nests made of a queen and her daughters.

In 2006, news broke of a crisis to bees- Colony Collapse Disorder. Data from beekeepers showed a decline of nearly a third of honeybee populations from 1989 to 2008. Several factors were identified including over-application of pesticides, the introduction of the Varroa mite to European honeybees, and the several disease outbreaks from hive transportation. Since 2008, honeybee populations have been recovering thanks to many of these threats being identified and mitigated. While this is a great success story for the domestic honeybees, research into our native bees’ populations is only just beginning. In addition to many of the same threats, native bees also suffer from habitat loss, resource scarcity, and competition with introduced species. In very recent years, lots of important research is being published, putting native bees in the spotlight of conservation efforts.

The Pugnacious Leafcutter Bee, Megachile pugnata, is an Aster family specialist. Female leafcutters use their large shear-like mandibles to cut circular flakes from leaves, which she uses to line her brood cells. Rather than a single nest with several brood cells, leafcutters typically build several dispersed brood cells in dead, hollow plant stems and other preexisting holes in plants.

If you have a garden, you can help support native bees just by being a lazy gardener. Instead of pulling weeds, do a quick search to see if that plant supports native species and only remove the invasive weeds. Try to support a variety of native wildflowers. Leave clippings on the edges of the garden to provide habitat and resources to nest-building bees. And avoid using toxic pesticides- by supporting a variety of species, they may begin to self-regulate. But an easy way we can all help out the native bees is just by learning a little about them, and checking in on them once in a while. So take a moment this spring and summer to appreciate some of nature’s hardest workers for all the beeauty they make possible.

Bringing Nature Home

"Chances are, you have never thought of your garden — indeed, of all of the space on your property — as a wildlife preserve that represents the last chance we have for sustaining plants and animals that were once common throughout the U.S. But that is exactly the role our suburban landscapes are now playing and will play even more in the near future."  Doug Tallamy

BRDC's April Book Club selection is Bringing Nature Home by Doug Tallamy with an optional presentation.

April's Book Club meeting will be Monday, April 25, 2016, 5:00-6:00pm. The Book Club is held in a private home, please call 276.293.1232 for more information.

Join the discussion.

(August 2014) 5. The Living Landscape: Designing for Beauty and Biodiversity in the Home Garden, by Rick Darke & Doug Tallamy

"A home garden is often seen as separate from the natural world surrounding it. In truth, it is actually just one part of a larger landscape that is made up of many living layers. And the replacement of the rich layers of native flora with turf grass greatly diminishes a garden’s biological diversity and ecological function. 

The Living Landscape seeks to reverse this trend by showing gardeners how to create a landscape that is full of life. Written by Rick Darke and Douglas W. Tallamy, two of the most important voices in sustainability and horticulture, it is the definitive guide to designing a beautiful, biodiverse home garden. The authors first explain the layers of the landscape and what role the plants within them plays in the larger environment, from providing berries for birds, food for bugs, or a place for bees to pollinate. The authors then put this information into context and offer design strategies to implement in a home garden. Helpful charts suggest plants, including natives and nonnatives, for each region.  

Douglas W. Tallamy’s award-winning Bringing Nature Home revealed the pressing need for a biodiverse home landscape. In a gorgeously illustrated, inspirational, and practical way, The Living Landscape supports the important message by showing gardeners how to make it happen."

For those who would like to include another book for this month's reading we are also suggesting this book: The New American Landscape: Leading Voices on the Future of Sustainable Gardening, edited by Thomas Christopher.

"Gardeners are the front line of defense in our struggle to tackle the problems of global warming, loss of habitat, water shortages, and shrinking biodiversity.  In The New American Landscape, author and editor Thomas Christopher brings together the best thinkers on the topic of gardening sustainably, and asks them to describe the future of the sustainable landscape. The discussion unfolds from there, and what results is a collective vision as eloquent as it is diverse.

The New American Landscape offers designers a roadmap to a beautiful garden that improves, not degrades the environment. It’s a provocative manifesto about the important role gardens play in creating a more sustainable future that no professional garden designer can afford to miss. " 

- John Greenlee and Neil Diboll on the new American meadow garden.
- Rick Darke on balancing natives and exotics in the garden.
- Doug Tallamy on landscapes that welcome wildlife.
- Eric Toensmeier on the sustainable edible garden.
- David Wolfe on gardening sustainable with a changing climate.
- Elaine Ingham on managing soil health.
- David Deardorff and Kathryn Wadsworth on sustainable pest solutions.
- Ed Snodgrass and Linda McIntyre on green roofs in the sustainable residential landscape.
- Thomas Christopher on waterwise gardens.
- Toby Hemenway on whole system garden design.
- The Sustainable Site Initiative on the managing the home landscape as a sustainable site.