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.
Photo courtesy D. Gordon E. Robertson.
A version of this story first appeared on the Adirondack Almanack in 2012.