The King

A friend once suggested that I write more stories about insects.   I reminded him that insects are not a topic of polite conversation in Maine unless we are griping about ravenous mosquitoes, invasive brown tail moths or swarming black flies (often suggested with tongue in cheek as the next state bird).  Don’t get me wrong, I get a kick out of watching lightning bugs in July and was pretty excited to capture a hummingbird moth on camera.  Still, at heart I am more of a mammal, fish and bird guy.

There is, however, one insect that has earned nearly universal esteem and not just from lepidopterists.  The large butterfly called monarch is a favorite across North America with a raft of citizen science and support groups, e.g., Project Monarch Health, Journey North, the Xerces Society and the Monarch Larva Monitoring Project.  A search for “monarch butterfly” on Amazon yielded 2,000 products including jewelry, oven mitts, Halloween costumes and kits for growing monarchs in your home.  All of that for a fragile creature that weighs one gram and lives just four weeks.  Fortunately the monarch has an amazing story for us.

History is unclear as to how this monarch was crowned.  One theory is that it was named after England’s King William III (1689 – 1702), known as the Prince of Orange.  That rings true because in 1780 Polish entomologist Jan Krzystof Kluk placed the monarch in a new genus called Danaus after a mythical king of Egypt.  Today scientists recognize three species of monarch: our N. American monarch, Danaus plexippus; the S. American monarch, D. erippus; and the Jamaican monarch, D. cleophile.  There is no doubt that the monarch is the king of butterflies, with fans around the world – it has even been bred on the International Space Station!

Colloquial names for the monarch include common tiger, wanderer and milkweed butterfly.  The last one makes sense because the story of the monarch is inextricably tied to the milkweed plant.  The monarch has evolved so that the female lays her eggs under the leaves of just one family of plants, the milkweeds.  If the milkweed plants are depleted the monarch suffers.  Let us look at the monarch life cycle to understand this phenomenon.

Butterflies pass through four stages of dramatic change in their life span, each change called a metamorphosis.  It begins with courtship as the larger, brighter colored male pursues his chosen female and forces her to the ground where they mate.  The spermatophores transferred from male to female trigger fertilization while providing the female with nutrition to sustain her through egg production and laying.  The eggs are so small that the featherweight female can produce as many as 1,000 over a few days.  If she mates several times her egg count goes up and increases their chances of survival, estimated to be just ten percent.

Each egg is laid on the underside of a milkweed leaf, and the female disperses her eggs to as many milkweed plants as possible.  Within days the eggs hatch as tiny larvae, more commonly known as caterpillars.  The caterpillars pass five stages of growth and molting of their skin.  Properly called caterpillar instars, they dine voraciously on milkweed leaves to bulk up on fats and other nutrients.  Depending on weather conditions each instar stage lasts three to five days.  Each successive instar has different coloration.  After the fifth instar stage the caterpillar is two inches long and weighs 2000 times more than at birth.  They now display distinctive black, yellow and white banding.

The pupation metamorphosis begins with the caterpillars spinning a sticky silk pad on the underside of a branch or other surface.  The caterpillars reverse ends to grab the silk pad with their hindlegs and hang upside down in the shape of the letter J.  Half a day later the caterpillar suddenly straightens and its skin begins to split behind its head.  In a few minutes the skin is shed to reveal the next life stage, a light green-colored chrysalis with bright yellow dots around the bottom.

The chrysalis hangs in place up to two weeks while wondrous changes occur inside.  When it finally matures the chrysalis becomes a transparent blue and inside it is possible to see the colors of the developing butterfly.  Once the butterfly has worked its way out of the chrysalis its wings are damp, requiring some hang time to dry and firm so they can withstand the pressures of flight.  The new monarchs seek out flowering plants for life-sustaining nectar.  The butterfly reaches sexual maturity in five days and the cycle begins all over again, a few times each year.

Monarchs live in a world where most insects are devoured as food.  How can the monarch focus its energy on breeding and metamorphosis without being snatched by a bird?  In the natural world some of the most colorful insects are the least palatable to predator species.  Those milkweed leaves contain special chemicals called cardenolides which are stored by the caterpillars for defensive purposes.  The cardenolides are toxic to most other species, resulting in a foul taste and digestive problems so significant that the predator avoids eating the caterpillars.  Some toxicity carries over to the butterfly stage offering protection until breeding is complete.  Only a few creatures can handle the toxins in small doses, among them orioles, robins and mice.

In late August a special generation of monarchs is born, sometimes called the Methuselah monarchs after the Biblical figure reported to have lived 969 years.  Rather than the normal four weeks life span these butterflies live up to nine months, long enough to make a 3,000 mile journey from Maine to a forest of oyamel trees in Michoacan, Mexico.  Flying an average 75 miles daily the monarchs travel in colonies up to 20 million strong, fighting wind and rain, feeding on nectar when available, roosting at night.  Once they arrive in November the monarchs cluster so densely that the trees almost disappear from view, delighting tourists who flock to the area.  The butterflies rest until February when they gather their strength to breed and lay eggs for the next generation.  All of the butterflies depart in March, needing three or four generations to get home but the Methuselah monarchs die along the way.  Scientists have yet to discover the secrets of how the Methuselahs are born every few generations, and how succeeding generations find their way to northern homes or back to Michoacan.

There are increasing concerns about the future of the monarchs of North America.  Populations in the western US have fallen precipitously, as much as 99 percent in the last two decades.  In the central US monarchs have been heavily impacted by industrial farming practices with herbicides that play a role in milkweed decline that has been ongoing for decades.  While the total US population of monarchs has been estimated at 200 million, the historic population was well in excess of one billion.  In recent years illegal harvesting of the forests in Michoacan has reduced the stands of oyamel trees by more than 90 percent.  The Mexican government responded by creating the Mariposa Monarca Biosphere Reserve, seeing the value of rising tourism to the area.  Recognized in 2008 as a World Heritage Site it is hoped that enough habitat can be preserved or restored to prevent a collapse in the monarch population.

Monarchs have earned sufficient fame to be named the official insect of seven states and there were two attempts to make it the national insect during the 1990’s.  As the public has become informed about the monarch life cycle and threats to their existence new conservation efforts have arisen.  Additional reserves have been created in states like California and Texas to limit habitat destruction.  There is a growing movement to increase the planting of milkweed along travel corridors used by the migrating butterflies.  Many people have chosen to raise monarchs in captivity with the intent of releasing them in hopes of boosting the population.  These efforts are controversial because of evidence that the released monarchs are less robust than wild butterflies, making them more susceptible to parasites and less able to make grueling migration flights.

Monarchs play a vital role in pollination, a process critical to the production of as much as 70 percent of the foods we eat.  Pollution and invasive predator species have caused pollinators such as bees to decline significantly in recent decades.  In response the Center for Biological Diversity and the Center for Food Safety filed in 2014 a petition requesting the US Fish & Wildlife Service to consider protection of monarchs under the Endangered Species Act.  In 2015 the federal Pollinator Health Task Force issued a National Strategy to Promote the Health of Honey Bees and Other Pollinators.  One goal was to restore or enhance seven million acres of land for pollinators through federal action along with public/private partnerships.  I qualified for funding from the USDA’s National Resources Conservation Service to create two large pollinator plots in a field, using a mixture of plants that bloom from spring into autumn.  Those plots now come alive with all kinds of beetles, moths, bees and butterflies including monarchs.

On December 15, 2020 USFWS ruled that listing monarchs as threatened or endangered was “warranted but precluded” because there are already 161 higher priority species in need of assistance from limited federal budgets.  USFWS plans to reconsider monarchs each year to see if priorities change and in 2024 will make a final determination whether to list the monarchs.  Supporters of the monarch are hoping the butterfly can hang on despite further declines – counts of overwintering butterflies in California by the Xerces Society have plunged in the last two years from 30,000 to an estimated 2,000 in December 2020.

There is one more concern to list here, a relatively new invasive plant in Maine.  Black swallow-wort was introduced in Massachusetts in the 1850’s as an ornamental plant from southern Europe.  As with so many other imports the plant proved to be aggressive and has been spreading ever since.  Black swallow-wort grows rapidly as a vine, similar to oriental bittersweet, and is capable of smothering native plants.  Worse, the plant produces stimuli similar to those of milkweed resulting in the monarch laying eggs on the leaves.  Studies have shown that 100 percent of monarch caterpillars ingesting the black swallow-wort leaves will die.

The news reports for the beloved monarch are discouraging but we can all support conservation efforts in progress around the country.  Many people have taken action at home by planting pollinator gardens to provide sources of nectar for butterflies and other insects.  In our region monarchs are known to favor common milkweed (Asclepias syriaca) so finding room for some of that plant on your property can make a difference for our winged friends.

If you like Ed Robinson’s writing, check out his two Nature Notes books! Click here for more information.