During a recent visit to the alpine garden trail where at this time of year the Bigelow Sedge, Deer Hair Sedge, and Three Forked Rush are golden and gleaming in the sun, a furry caterpillar was spotted on the trail.
Caterpillars are intriguing because they are beautiful and bear no resemblance to their airborne counterparts. They undergo a traumatic and exquisite change during their life cycle that transforms them from a terrestrial insect to one that can fly.
The life cycle of a moth or butterfly is intricate. All true butterflies and moths undergo a process called metamorphosis, which is a grand transformation through four phases from an egg to an adult. The egg is laid by an adult on or near a substrate that the caterpillar feeds on. The egg phase lasts from six to fourteen days depending on the species of moth or butterfly, and whether or not the eggs are over-wintering. When the eggs hatch, larvae called caterpillars emerge.
The caterpillar is the growth stage of this insect, during which the caterpillar functions as an eating machine. In some species the caterpillar increases its body mass by 1000 times! With this change in size the caterpillar must molt, or shed, its skin to accommodate itself. The larva usually molts from five to six times. The larval stage between each molt is called an instar. After the final molt the instar begins its journey into pupation by building a protective and fixed cell around itself. A butterfly larva builds a cell called a chrysalis that usually hangs off of a plant branch or another structure; a moth larva builds a cell called a cocoon that is wrapped in many fibers of silk and looks like a small, elliptical pillow, usually in leaf litter or soil.
Within the cocoon or chrysalis, a dramatic change transpires: the larva becomes a pupa which then rapidly transforms into an adult. Most of the larva’s tissues and organs are absorbed and rearranged into the adult body structure. In some species the pupal stage lasts for seven to fourteen days, while other species pupate for over a year. This is the case for the furry caterpillar that was seen in the Alpine Garden. The name of this caterpillar is the Great Tiger Moth Caterpillar (a threatening name for such a cuddly-looking fellow), Arctia caja. It is also referred to as a “woolly bear” caterpillar because of its soft, woolly looking body.
The Great Tiger woolly bear can be found moving on rocks or on its food source. Foods that this caterpillar enjoys munching are extensive, as the woolly bear is polyphagous, meaning that it eats a variety of foods. Such foods include alder, cherry, lilac, and willow leaves, although up in the alpine zone few of these woody plants exist.
This caterpillar is an arctic species, meaning that its habitat is arctic tundra, which is similar to the environment above treeline. This also means that tree line is the lower boundary of this moth and of several other moth and butterfly species found in alpine communities. If the climate grows warmer over time and the lower boundary of the alpine zone elevates, these arctic species will have no where to go and will perish.
If the Great Tiger Moth caterpillar is spotted during a hike on the alpine garden trail, observe the furry creature and handle it gently if you wish. Soon this caterpillar will find a cozy place underneath rocks, soil, or plants, where it will hibernate for the winter in the larval form. In May or June when the snow begins to melt, the caterpillar will exit its sanctuary, finish developing as a larva, and then build a cocoon for the transformation into adulthood. These caterpillars, just like other alpine animals and alpine plants, withstand trying conditions during their lives above treeline. Please be respectful of all plants and wildlife by hiking on the trail and handling them with care!
AMC Naturalist Guide
Wagner, D.L. Caterpillars of Eastern North America. Princeton: Princeton University Press, 2005.
Bell, Allison and Slack, S.G. Field Guide to the New England Alpine Summits. Boston: Appalachian Mountain Club, 1995.
Bug Guide. Iowa State University Entomology. September 12, 2010 http://bugguide.net/node/view/26615.