Monarch Butterfly Migration is a Mystery
Les Harrison is the Wakulla County
Monarch butterflies, Danaus plexippus, are likely the best known butterflies on the planet because of their remarkable ability to migrate thousands of miles across international borders to congregate in the same spot year after year.
Their bright colors and animated appearance make them the prototypical image for this popular insect order.
This curious behavior has its origins obscured by the mist of time. The theory goes that the last Pleistocene glaciations in North America instigated migration to Mexico in the east and to the Californian coast and deserts in the west.
In the western U.S., the overwintering colonies are smaller and more numerous, while in Mexico, they are few but more spectacular, with billions of butterflies concentrating in one spot.
The residents of Wakulla County are fortunate to be in the path of the assemblage and can see many of the flyers heading south for the winter.
Monarch butterflies are found throughout the Americas and in Australia. There have been a few reports of individual sighting in New Guinea and Western Europe.
Year around populations are found in Mexico, and Central and South America. Permanent populations have been confirmed in south and central Florida where frost and freezing temperatures are a rarity.
Monarchs lay their eggs individually on the underside of leaves and sometimes on the flowers of different milkweed species. There are several native and exotic milkweeds which grow wild in Wakulla County.
These one-at-a-time deposits have several benefits for the larva which hatch. The most notable is that the voracious insects have plenty to eat with little chance of competition from their own species for the increasing scarce dietary resource.
While milkweed has an attractive bloom, it quickly goes to seed.
As such the plant is relegated to wildflower status, sometimes being destroyed as a pest, and was rarely cultivated until recent years.
Additionally, the wide distribution of the eggs improves the chances at least some of the eggs will hatch and reach maturity.
Monarchs are exclusively vegetarian and not an apex predator.
Invertebrate pillagers such as ants, spiders, and wasps attack monarch larvae on milkweed plants. Tachinid flies and braconid wasps are known to parasitize larvae.
To add to the odds against survival of the eggs and larva, there are several microscopic organisms which can infect monarchs during their formative stages. These including a virus, multiple bacteria, and protozoan parasites.
At the hatching of the first instar, or larval phase, the tiny caterpillar is white with a black head. There is a touch of irony when such a colorful butterfly begins life in this monochromatic form.
Development from the white egg to the adult’s brilliant splender takes less than a month.
In North America, the monarchs go through at least four generations a year before they start the migratory trek south in the autumn.
Adult Monarchs are strong fliers that can stay aloft for 11 consecutive hours. In the fall, mature Monarchs have enough fat stored up from plant nectar to permit a continuous flight of over 600 miles without feeding.
There has been a concerted effort to cultivate milkweed and nectar producing wildflower in the area by Wakulla County Master Gardeners and others who hope to see Monarchs continue their transcontinental flight.
To learn more about helping the Monarchs in Wakulla County, contact your UF/IFAS Wakulla Extension Office at (850) 926-3931 or http://blogs.ifas.ufl.edu/wakullaco.