Caterpillars are frequently collected by students for science classes, or by parents to show their little ones the amazing change from caterpillar to butterfly or moth. You may have done this before with a Monarch or Swallowtail caterpillar or chrysalis during the summer. Some moths and butterflies don’t head South like Monarchs, but instead “overwinter” in your yard. That means you also can start this activity in the fall with other species, but you will have to wait until spring to see it completed.
Collecting and containing caterpillars
How these living organisms are collected and handled makes all the difference in project success. Most of our caterpillars are found late summer and early fall, being nearly full grown out in the yard. At that time, they are big enough to be easily spotted in the garden or shrub bed. (It may be too late in northern Illinois, but may still be timely for the southern part of the state).
The caterpillars, such as Cecropia moth, can be brought indoors and gently placed into a terrarium, if you have one, or a large canning jar with holes poked in the lid. You also need to include the foliage from where you found them. Placing some soil at the bottom of the container is a good idea too since many moths will pupate in the ground.
Since they are full grown or nearly so, they feed for a short time before beginning their journey from caterpillar to adult butterfly or moth. With many moth species, the pupae are inside of what we call a cocoon, and in general, butterflies form a chrysalis. When working with a caterpillar, you will be able to see them transform into an over-wintering stage called a pupa.
Note: Do not do this project with Woolly Bear caterpillars, as they overwinter as caterpillars and pupate in the spring. But you can try this cool weather-related project with Woolly Bear caterpillars.
Finding and protecting pupae
If you miss the mature caterpillar, you can still find their cocoons already attached to twigs, like with the Cecropia moth. Take in the twig, cocoon and all. It may be easier to find these when our leaves turn colors and drop, so keep an eye out while raking up those leaves. (Pupae without a cocoon covering will be much harder to spot.)
Typically, moth pupae are a reddish-brown structure when they will not feed anymore. This is how it is going to look for several months until nature signals the emergence of the adult next spring. While it looks like nothing is going on, there are lots of changes occurring inside transforming the caterpillar.
So far, all this goes on at room temperature, similar to our outdoor temperatures. However, from this point forward, all of those pupae need to experience the colder temperatures of our winter in order to make the change.
Pupa should be placed in containers that keep out mice, shrews, and other small animals that would otherwise find them a good choice for dinner. Again, those canning jars with a lid and ring work well with a few small holes punched in the lid. The container can be placed outside at the base of shrubs or perennials, covered with leaf litter to experience the needed cold weather. They also could be stored in an unheated garage or porch.
Once spring arrives, retrieve the containers and place the pupae back into a larger container with some branches. Within a few more weeks, pupae will have emerging butterflies and moths. They will need those branches you placed in the larger container or terrarium to climb onto to allow expansion and drying of their wings. This timeframe should coincide with what is happening outdoors so after a few hours of being amazed at the transition, it is best to release the butterflies and moths back into the backyard.
About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.