by Roy Lukes

Marvelous Monarch Summer Coming To Close

male monarch buttergly
Male monarch butterfly showing scent scale pockets on wings and claspers at tip of abdomen

One of the best summers for Monarch butterflies in this region in recent years is gradually coming to an end. Nearly everyone we’ve talked butterflies with has seen many of them. One friend of ours, who lives with her family near Fremont, reported counting 24 Monarch caterpillars being supported over a several-week period by one large white Swamp Milkweed plant. A few days ago Charlotte and I estimated over 100 Monarchs feasting on the nectar of Bur Marigold growing in huge patches in the wetland to the north of Anclam Road on the east side of Baileys Harbor Bay.

Flowers rich with energy-providing nectar are vital to the migrating Monarchs as they slowly make their way toward Mexico where they will spend around five months of the winter. Goldenrods are one of the best groups of weedy wildflowers on which they feed. Several of the tall composites that many people include in their gardens are also very good. Included are Purple Coneflowers, Zinnias, Tithonias (Mexican sunflower), and Rudbeckias. Interestingly, the sweetest nectar is produced on sunny still days. Rain and overhead watering tend to dilute the nectar, thereby reducing its overall benefit to the Monarchs.

It was during the fall of 1997 that eastern Wisconsin experienced such a large migration of these strong fliers. Six Monarchs feasted on our Tithonias on Sept. 18. One of our best counts of 18 occurred as we biked on Washington Island on Oct. 3. You can imagine our pleasant surprise of seeing our last migrating Monarch at Toft Point on Oct. 19, the latest we’ve ever seen one in this area.

It’s quite extraordinary that a butterfly, weighing about one-half of one gram (one fiftieth of an ounce), can fly somewhat over 2000 miles to its wintering site in the mountains west of Mexico City. Even though their flight is slow, it’s very powerful, described as being a soaring, gliding flight that makes use of rising air masses and tail winds, similar to that of many migrating hawks.

Estimates are that several hundred million Monarchs, up to five generations removed from the Monarchs that successfully made the trip northward last year, will astoundingly find the same wintering sites used by their ancestors for many years. Bear in mind that obviously these migrating butterflies have neither flown that great a distance nor have ever been to these famous mountainous forests before.

Today, Sept. 12, several Monarch chrysalides remain attached to the siding of our house or the underside edge of our deck, and one large larva rests upon a milkweed leaf, apparently ready to change into its chrysalis form.

A general assessment of butterflies is that they are fairly non-violent – with the exception of the male Monarch, among a few others. On occasions he is known to attack a female quite viciously during mating. During their breeding season the males, whose sole purpose in life is to fertilize the females, tend to remain in the vicinity of good nectar-producing flowers that are bound to attract some females. The females are much more intent on locating young healthy milkweed plants upon which to lay their eggs, but the females also must drink plenty of nectar in order to keep up their strength. Searching for suitable plants, then laying eggs, requires much energy.

A male Monarch is equipped with several fascinating body features that help him to attract and secure a female. Contained within his anus is a pair of yellow scent glands that are covered with fine long hairs. These glands, like tiny little rods or pencils, contain the extensile hairs which help to disseminate a flowery odor. The male can extend or retract these glands at will. When fully extended they emit a strong, sweet, spirea or honey-like odor.

Located on the upper surface along one of the thin black veins of each hind wing of the male Monarch are small, black, scent receptors, sometimes referred to as scent-scale pockets. Into these oval chambers, containing absorbent scales that act somewhat like blotting paper, the male deposits minute quantities of the clear, yellow, sweet-smelling fluid from his anal scent glands.

Encircling the male’s posterior end are tiny, inward-curving, jaw-like abdominal claspers. Flying close to a female, the male extends his scent glands and tricks her into following him to a good source of nectar. After alighting upon a leaf the male now must grasp the posterior end of the female’s abdomen with his claspers. However, he cannot do this until his scent glands have been retracted into his body, thereby immediately cutting off the fake nectar aroma. Without this alluring scent, the female would quickly lose interest and fly away.

It is now that the scent-scale pockets located on his rear wings come into play. Quickly the male, using his hind legs, brushes some of the scented scales from the pockets into the surrounding air, in so doing keeping the female close to his side, and giving him that split second of time in which to grasp onto the tip of her abdomen. Now she will receive the sperm cells from the male, ensuring the fact that eventually her eggs will be quite wonderfully transformed into the adult Monarchs that will successfully perpetuate their race and eventually migrate to Mexico.

There is little wonder that so many of us wish the Monarch Butterfly could become our national insect. What a marvelous creature!

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This column appeared in the Door County Advocate on 09/17/1999.
© Copyright 1999 Roy Lukes. All rights reserved.