You've Found a Caterpillar - Now What?

Caterpillars are fascinating creatures in their own right and represent a vital stage in the life cycle of some of our most remarkable insects. The long and short of it is that caterpillars range in length from about one-fourth to five inches long. Diversity in size is rivaled only by their vast array of colors and patterns. Black, brown, green, red, orange, yellow, and blue among others, combine to form bands, rings, dots, and patches on caterpillars. If this weren't enough, projections of all sorts including hairs, spines, bumps, and horns lend to the distinctive look of caterpillars.
Caterpillars are everywhere consuming a great variety of plants that sustain them on their journey from egg to adult. Typically, caterpillars feed on foliage, but also eat flowers, roots, seeds, and fruits. Rarely, they may utilize wood, moss, fungi, and woolly aphids. Amazingly, some caterpillars are small enough to live within the flat layers of a leaf or actually breathe oxygen underwater! Often incorrectly referred to as worms, caterpillars are the larval stage of moths and butterflies.
Finding caterpillars is fun! Beyond observing them or snapping a photograph, why not rear one? Complete metamorphosis demonstrated by this order (Lepidoptera) is a fascinating experience that kids, in particular, won't forget. Basic principles of physiology, ecology, and insect behavior can be learned by rearing caterpillars. The life cycle may be studied in as much or little detail as you like. Rearing caterpillars also makes an engrossing low-cost science project for school.
If you find a caterpillar on a plant, do not pull it off the stem or leaf. Many caterpillars tighten their grip when threatened and damage will occur to the caterpillar. Instead, remove the leaf by the petiole or take a small section of the plant and place it in any container you may have with you. Carefully note the exact location and name (if possible) of the food plant for future use. Scoop-up a wandering caterpillar in a container. Generally speaking, smooth caterpillars may be touched. Do not handle spiny caterpillars. Fluid from the spines may cause stinging and rashes. More so, hairs found on other caterpillars can be very irritating when introduced in the eyes. On the way home, make sure the lid is secure and keep the container out of the sun.
Many items you probably have at home make excellent rearing containers. Plastic boxes such as those used for food or shoes are ideal. There's also plastic cups with lids, glass jars, aquariums, or screened cages. All lids must have vent holes for air exchange. A steady supply of fresh food is critical to rearing the caterpillar. If you were lucky enough to find the caterpillar on its foodplant, then you already know what to feed it. Continue to supply the same kind of leaves. If the caterpillar was on-the-move, offer an assortment of leaves from surrounding trees and other plants. Black cherry, oak, birch, willow, sweet gum, and plantain may be accepted. Some caterpillars are general feeders, while others are quite picky. Rinse the leaves in water and dry them before offering them to your guest. Depending on the "wilt-factor" of the leaves and how fast the caterpillar is eating them, a leaf or two may be added as needed with no special care. To keep them fresh, leaves can be pushed into a small container containing damp sand or the petiole or branch can be wrapped in moist paper towel.
Like all insects, caterpillars have an exoskeleton. As the caterpillar grows, the exoskeleton can only stretch so much. At certain intervals, your caterpillar will remain motionless for a day or two and molt. This process replaces the old skin with a new one. A molting caterpillar is very vulnerable and may appear sickly. Interfering with this process could harm the caterpillar. Startling appearance changes are common after a molt; don't miss it. The interval between each molt is called an instar.
Keep the container free of frass (caterpillar droppings), well-ventilated, uncrowded, and out of direct sunlight. Don't be discouraged if your caterpillar dies. Diseases caused by bacteria, viruses, and other pathogens often kill caterpillars. Also, prior to collecting your caterpillar, certain species of flies or wasps may have parasitized the insect. If this is so, only a fly or wasp will be produced.
When the caterpillar matures, noticeable changes can be seen. The now sated caterpillar stops eating, excretes undigested food, shrinks slightly, and may develop a red or yellow hue. At this time, place several upright sticks in your rearing container. Also add a small amount of leaf-litter and several inches of substrate such as soil, sand, or peat moss to the bottom of the container for those caterpillars that pupate at ground level or below.
After the caterpillar has pupated, there's no need to move the container. Your conscientious care should be rewarded by the emergence of a beautiful, new moth or butterfly. Enjoy the pleasure of releasing the butterfly by day or the moth by night in the area where you found its caterpillar. You can also start an insect collection. Many young people develop a lifelong interest in nature or careers in biology or entomology through insect collecting.