Wednesday, June 6, 2012

The White Admiral Butterfly

Forest clearings in the Adirondacks are especially attractive settings for many forms of wildlife. The warmth of the ground when the sun is shining is particularly inviting to cold-blooded creatures, and the stands of trees that surround these openings in the canopy serve as a source of food and shelter.

Clearings created during logging operations, wide sections along secondary roads, and the open space that typically exists around lean-tos and campsites are places frequented by numerous animals. Among the creatures easily observed during the coming month in these sunny oases of our deciduous and mixed woodlands is a strikingly attractive, black butterfly with a distinct white strip across its wings. The white admiral butterfly (Limenitis arthemis) is a common component of our fauna and regularly lingers around small forest clearings during the early summer throughout the Park.

The white admiral passes the winter as a small, immature caterpillar inside a leafy shelter, which it constructs on many species of hardwood trees. As the length of daylight significantly dwindles in late summer, the larvae or caterpillar selects a leaf and firmly attaches the stem of this green structure to the twig with multiple threads of silk. This prevents the leaf from dropping to the ground when autumn arrives. The approximately inch long bug then aligns itself with the central vein and chews off the end and most of the sides of the leaf. It then pulls the remaining piece of the blade around its cylindrical body, forming a small tube. Silk threads are now used to hold the seam together.

This leafy cocoon serves as home to the caterpillar for the entire winter, keeping its body hidden from the sight of those birds that prowl the forest canopy for anything they can find to eat. Even though the surrounding air temperature may frequently drop well below zero for extended periods throughout winter, the state of diapause which this bug enters allows its body tissues to remain alive during this dormant period without suffering any harmful effects.

As spring arrives and tender new foliage emerges from buds, the caterpillar exits its cigarette-butt size retreat and quickly starts to consume young green matter. Since newly sprouted leaves in spring are easier to chew than older foliage and contain a greater concentration of nutrients for this developing insect, the caterpillar’s strategy for delaying development until spring contributes greatly to its ecological success.

After the caterpillar becomes fully developed, it then enters the pupa stage of its life cycle. It takes roughly two weeks for the body of this insect to metamorphosize into an adult, as temperature is the key factor in determining the rate of development.

Unlike many butterflies that obtain nourishment from flower nectar, the white admiral is known to extract much of the water and nutrient it requires from deposits of animal excrement that it locates with sensory cells concentrated on its antennae. Because forest clearings are often visited by many larger creatures, like deer, bears, raccoons and coyotes under the cover of darkness, fresh piles of waste are often available to this insect in the morning as it patrols these open places for any such dung. Additionally, many smaller animals, like ermine, voles and mice frequent forest clearings, and their wastes are also used by the white admiral. Rotting fruit and vegetable matter is consumed by the white admiral if such matter is available, and excrement can not be located.

While the white admiral is easy for a human to see, the white stripe across its wings helps to break up the outline of its body as it rests on the ground, or in a tree. This illustrates a form of protective camouflage known as disruptive coloration and is most effective on color blind predators, especially those that target butterflies and other similar sized bugs. In more temperate regions, many white admirals possess a color scheme that closely resembles the pipevine swallowtail butterfly, which is avoided by predators because of its bad taste. Because the pipevine butterfly does not occur this far north, the white admiral relies solely on disruptive coloration to prevent being preyed upon by butterfly-eating members of our wildlife community.

Over the next month, the white admiral butterfly will be fluttering about small forest clearings throughout the Park. When passing through such settings it is always enjoyably to stop and look for this attractive insect, provided that the emerging deer flies will let you.

Photo courtesy Wikipedia.

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Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.


2 Responses

  1. Mick says:

    Tom, Does the White Admiral prefer this habitat because of the new growth? I understand this is the preferred habitat for the Bicknell’s Thrush as well. I’ve read that there is greater biodiversity on “edge” habitat like this. Any information?

    Great article. Thanks.


  2. Tom Kalinowski says:

    Hi Mike: Thanks for reading the Almanack. The main reason that I believe that the white admiral is drawn to hardwood forest edges is the greater abundance of dung in those settings. I am not sure of the areas that the Bichnell’s thrush prefers other than dense balsam fir and spruce forests. It wouldn’t surprise me that this rare thrush does favor edge settings within upper elevation forests, as the density of foliage is greater in these places, which does help provide an increased biodiversity.

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