Common Green Darners Migrating South
Monarchs aren’t the only insect that are seasonal migrants. The Common Green Darner dragonfly and a few other dragonfly species are as well. However, where Monarchs move northward in the spring over several generations, one generation of Common Green Darners flies all the way from southern U.S., Mexico and the Caribbean in the spring to New England and Canada. Here they lay eggs which give rise to a second generation that migrates south in September and October. Upon reaching their destination they then breed. A third generation emerges around November and lives entirely in the south during winter. It’s their offspring that start the cycle again by swarming northward as temperatures warm in the spring.
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Monarch Roosts
Monarch migration is in full swing. Some of the migrating butterflies from the Northeast travel as far as 3,000 miles to reach their winter destination in the Sierra Madre Mountains of Mexico. In addition to finding sources of nectar along their migration pathways to build their fat reserves Monarchs must also seek shelter at night, roosting on land when it cools down and they can no longer fly.
It appears that roosting is critical for migrating Monarch survival. Just before dark these solitary diurnal migrants gather in clusters called roosts. A roost can consist of just a few butterflies up to thousands clinging to leaves and branches on a single tree. Cedar, fir, and pine are common species of trees used for roosts, but deciduous trees are also used.
Most roosting trees are along a principal flyway, located in a cool, moist area, provide shelter from the wind and are near a source of nectar. Often roosts last for only a night or two but can last a week or two. Monarchs can but do not necessarily use the same resting sites year after year. It’s generally accepted that these roosts are an anti-predation tactic, employing the strategy of safety in numbers. To see a map of documented 2021 roosts, go to Journey North’s site: https://maps.journeynorth.org/map/?map=monarch-roost-fall&year=2021.
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Monarchs Starting To Leave Mexico
The Monarchs’ migration north has begun! We are not the only part of the world that is experiencing unusually high temperatures — there has been a heat wave in Mexico this spring where the Monarchs overwinter, and it has them on the move, leaving their sanctuaries and beginning the more than 2,000 mile journey to New England.
This overwintering generation of Monarchs lays eggs in northern Mexico and southern U.S. and then dies. When their eggs hatch and develop into adults, usually by late April to early June, they continue the journey north that their parents began, laying eggs along the way. They begin to arrive in northern U. S. and southern Canada in late May.
To follow their progress northward, go to Journey North’s site, https://maps.journeynorth.org/map/?year=2020&map=monarch-adult-first. Although we probably won’t see any Monarchs in New England until the end of May at the earliest, it’s fun to be able to see exactly how far they have gotten as spring progresses. Journey North citizen scientists also monitor mammals, amphibians and birds. To participate in their research or to see their observations go to https://journeynorth.org/.
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Common Green Darners Appearing
The Common Green Darner (Anax junius) is one of our most common dragonflies. often seen near ponds. The family of dragonflies known as “darners” consists of species with large eyes and long abdomens that tend to rest infrequently and when they do rest, usually hang vertically. The Common Green Darner is the only North American darner in which the male and female usually fly in tandem when the female is laying her eggs on emergent vegetation.
Up to 50 of the world’s 5,200 dragonfly species migrate and the Common Green Darner is one of them. In the fall most (but not all) adult Common Green Darners migrate south to Florida, eastern Mexico and the West Indies. Huge clouds of migrating dragonflies have been seen along the East Coast, Gulf Coast and the Great lakes in autumn. Transmitters weighing 1/100th of an ounce that have been attached to migrating dragonflies confirm that they migrate much like birds. Just like avian migrators, they build up their fat reserves prior to migrating; they follow the same flyway as birds, along the Atlantic Coast; and like birds, dragonflies don’t fly every day but stop and rest every three days or so.
Some dragonflies mate and lay eggs along the way, while others do so when they reach their destination. The eggs hatch, larvae develop and the adults head north in the spring. Unlike birds, migration is only one-way for dragonflies. It is the offspring of the fall migrating generation that migrate north in the spring. Here in the Northeast, most arrive before any resident Common Green Darners have emerged. (photo: female Common Green Darner)
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Monarch Butterflies Reach Wintering Grounds
Two days ago, on November 6th, the first Monarch Butterflies arrived in their 73-mile-wide overwintering area in the Transvolcanic Mountains of Central Mexico. This miraculous flight, which takes a Monarch roughly two months, can be up to 3,000 miles long. Using the sun, and most likely the earth’s magnetic field, they head for specific stands of Oyamel Fir trees, where they will cluster and be protected, unless weather conditions are severe, from extreme temperatures, predators , rain and snow until next March, when their journey north begins. (These butterflies only get about half way back to New England, at which time they mate and lay eggs. The third or fourth generation of these monarchs will reach their eastern destination.) To track the migration of these remarkable insects, go to http://www.learner.org/jnorth/monarch/index.html.
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Common Green Darners Migrating
The Common Green Darner, Anax junius, is one of our largest dragonflies, measuring three inches long, with a four-inch wingspread. It is strikingly colored, with a green thorax and a bright blue (male) or reddish (female) abdomen. As if that weren’t enough to set this dragonfly apart, it is also migratory. Common Green Darners migrate south from August to November, stopping over (like migrating birds) occasionally along the way, resuming flight after resting and refueling. Thanks to radio telemetry, we now know that over a two-month migration, Common Green Darners, each weighing about one gram, can migrate over 400 miles. (Photograph is of a Common Green Darner perched on Bottle Gentian.)
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