Posted on 11 February 2016.
By Ranger Steve Mueller
Being hard to find has an advantage when you are a tasty morsel. Consider how tasty you are to female mosquitoes. Being thousands of times larger than a mosquito makes you an easy target. You make yourself an even easier target by expelling carbon dioxide and by giving off heat. If you quit breathing, mosquitoes will lose interest and your heat will quickly dissipate.
I do not recommend that tactic to avoid mosquitoes. Animals have many adaptations that actually provide improved survival chances. Being small is one advantage. It is difficult to find a creature that is less than one-fourth of an inch long. When the creature does not move for months, it makes it even more difficult to find.
The creature I am describing ties a willow leaf to a twig so, when fall leaf drop arrives, the leaf stays on the shrub. Silk from salivary glands becomes a strong binding thread when exposed to air.
During the summer months, this insect might have three broods of young. Summer broods hatch from a minute eggs and begin eating willow leaves. If fortunate, they are not eaten by Blue-winged Warblers, Indigo Buntings, ants, or stink bugs. It will pupate and transform from caterpillar to butterfly.
People often refer to the pupa as a resting stage but it is not. Tremendous work of changing its body from caterpillar to winged adult is accomplished in the chrysalis (pupa). Little rest takes place. If it is warm, the pupa will transform more rapidly and chances of becoming food for mice or other things is reduced. Less time in the chrysalis increases survival chances. It is likely that less than one percent survive from egg to adult. A primary ecological function of the adult is reproduction to keep its nature niche occupied in willow thickets.
Late season reproduction differs from earlier generations that feed heavily and work to transform to an adult as quickly as possible. The late season animal is affected by changing day length. On hatching, the egg prepares for a long resting sleep. First it must tie a leaf petiole to a twig so the leaf does not fall off as autumn progresses. It then wraps and binds itself in the small leaf with silk.
In its sleep chamber, it waits for new spring leaf growth. If it escapes a multitude of animals looking to eat it, it might get to feed and grow in spring’s warming sunlight. If we have a wet fall or early spring, fungus or bacteria might kill the small upstart. Surviving is tough.
During the long winter months, the caterpillar is actually in a deep sleep called diapause. It is hormone induced caused by shortening days and lengthening nights that bring chemical changes to its body. The hormones result in behavior different from summer broods.
Try to find one of these sleeping Viceroy butterfly caterpillars in a brown coiled leaf that looks like a leaf fragment attached to a willow twig. It is the work of birds to search twigs all winter in an effort to eat the insect. I feed birds all winter in hope of distracting them enough to help some Viceroys survive to grow, pupate, become an adult, and reproduce here at Ody Brook Nature Sanctuary.
The tiny caterpillar, about the size of a pencil’s visible lead, has a big challenge to survive a long winter sleep but its adaptations improve the odds. When it emerges from the crumbled leaf in spring, its color pattern looks much like a bird turd. When disturbed it arches its body and looks even more like a turd.
Develop observation skills and patience with the challenge of finding an overwintering caterpillar in its deep sleep. Take the family to a willow thicket and search the shrubs. My friend Ken is more skilled than me at finding them. The last one he found was on a willow shrub along the White Pine Trail.
Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at firstname.lastname@example.org – Ody Brook Nature Sanctuary, 13010 Northland Dr. Cedar Springs, MI 49319 or call 616-696-1753.