Mourning Cloak: An Unusual Butterfly

The last week in March was warmer in Detroit in 2021 than it is this year. On March 27 a year ago, I saw the first butterfly of the year in Eliza Howell Park, a Mourning Cloak, definitely one of my favorites.

Because it is one of the few butterfly species that spend the winter here as hibernating adults, it emerges as soon as it “thaws.” We do not need to wait for them to arrive (some butterflies migrate) or to complete development (some butterflies spend the winter as caterpillars or pupas). We just need some warmer weather.

Photo by Margaret Weber

Mourning g Cloaks are not rare, but they are not among the well-known butterflies. This may be becaise of their unusual life.

They emerge from hibernation (a winter spent under loose bark of trees, in log piles, etc.) in the Spring and begin to feed on tree sap, rotten fruit, and dung. Before long, they will mate, lays eggs on trees, and die. At this stage of their life, I usually see them in the woodland.

The new generation completes deveopment in June or perhaps early July. Last year, I spotted this one on June 24. It is on aspen leaves, one of the host species for their caterpillars, and may have just emerged from the chrysalis.

The new adults feed for a few weeks, but not often on flowers. They are usually seen on leaves or on the ground. This photo was taken on July 2 last year.

Mourning Cloaks are very long-lived for butterflies. The generation that emerged last June is the same generation that will be coming out of hibernation soon. They feed actively for a month or more as new adults before taking a “rest break.” They estivate (become dormant during dry weather) later in the Summer.

While Mourning Cloaks do not often visit flowers, I did watch one last July 17 as it acted very much like a nectarer, on a Purple Coneflower and then on a Wild Bergamot.

Following the period of estivation, Mourning Cloaks again feed in the Fall until time to hibernate.

The calendar of active time (marked in red) under the next photo helps to clarify the life pattern of the Mourning Cloak (Taken from Larry Weber, Butterflies of the North Woods, 2nd. edition.). I do not know of another Eliza Howell butterfly species with a similar life.

Mourning Cloak is a large butterfly, about 4 inches in wingspan, vary attractive, and not easily confused with any other species. And it is often the first butterfly seen in the spring. What is not to like!

My wish is that more people get to know this fascinating insect.

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