Rearing caterpillars at home

I get a lot of questions from butterfly enthusiasts who want to rear caterpillars at home and would like some instruction. My first response is usually to suggest rearing caterpillars outside in their gardens where natural processes can occur. A sad fact is that some caterpillars will be the victims of predation. In nature, butterflies and moths are near the edges of the food web and are important sources of nutrition for many animals. However, I understand the mystery of metamorphosis and love sharing that process with children and families.

The Challenges

Caterpillars can be challenging to rear because they are so well adapted to their environment. By brining them inside you introduce a whole new set of challenges for the caterpillars to overcome. Yes, they may be safer from predators, but consider these factors before bringing your caterpillars inside.

A caterpillar found wandering through a yard will probably make a poor candidate for indoor rearing. Unless you are certain what species of caterpillar you are dealing with, you will not know what host plants they require. Many caterpillars are specialists and can only consume a few species of plants. Try instead to find eggs on a plant like milkweed that will probably hatch into Monarchs or Queens. This way you know the species and the host plant to start and that will very much help your rearing experience. A wandering caterpillar may be looking for a new food source or may be looking for a nice place to pupate so take some pictures and let the larvae continue on its way.

Seven Days a Week: Caterpillars require attention every day. They don’t stop eating on weekends and don’t stop pooping while you are at work. Expect to spend about half an hour with your bugs each day.

Hungry Bugs: Caterpillars eat a lot. Take the amount you expect them to eat and triple it. By putting them in a tank you keep caterpillars from being able to wander to look for more food sources if they run out. This will require lots of plant material. After just one day you can expect that the nice fresh plant material that you added that morning or the previous night will look like the plants pictured in this photo. If left without food caterpillars may sicken or may begin to consume chrysalises of other caterpillars. This is pretty yucky and tough to explain to kids.

Toxins: Often, new plants purchased from a nursery may be treated with a biological pesticide agent even if they have not been “sprayed” with a commercial insecticide. In case you have to purchase more plants in the middle of caterpillar rearing, make sure you have located a small butterfly friendly nursery before hand and have talked with their staff about what you are doing. Household cleaners, even dishwashing soap, can sicken your caterpillars. You have to be mindful of any foreign agent that may contact your bugs.

Environmental Changes: By moving caterpillars into a tank or screen enclosure, you remove them from their habitat and sometimes it is more difficult for them to survive. By bringing the insects inside the temperature and humidity of their environment changes drastically which can sometimes have negative effects. Too low humidity can cause chrysalises to dry out. High humidity can lead to mold and fungal growth and rotting plant material.

Crowding and Disease: In a tank environment caterpillars are often more crowded than they are in the wild which makes them susceptible to a host of diseases they might otherwise never encounter. Caterpillars eat an enormous amount of food and produce endless amounts of frass (a nice way to say caterpillar poop). This frass can host diseases, grow mold of fungus if left too wet and should be removed daily.

Dormancy: Caterpillars and chrysalis that encounter a lower temperature suddenly may slow down and enter a type of dormancy called diapause. Caterpillars need an airy, well-lit environment that has a similar temperature to what they are accustomed.

The Basics of Caterpillars Rearing

Setting up a tank: What seems to work best for us here is to collect the live plant on which the eggs have been laid and to keep the stem in fresh water to make it last as long as possible. We cut plant stems and immediately place them into a water container (a yogurt cup with a small X cut into the lid works nicely) and change the water or re-cut the stem as needed to keep the plant fresh. By the time the plant wilts the caterpillar should be hatched and you can introduce new food plants.

Minimizing contact: Caterpillars can be fragile and sometimes likes to hold on to their host plants for dear life. By draping fresh stems over the wilting plant you will encourage the caterpillar to move to the fresher plant material with minimal contact.

Cleanliness: Once the caterpillar hatches and begins to eat, it is very important to clean their tank regularly. Use newspaper at the bottom of the tank so that waste can be removed quickly and clean the tank about once daily. Remove the paper, wash the tank with water and a sponge only (soap residue can coat a caterpillars body and make breathing difficult), put in a clean paper liner and replace the caterpillar and food plants. Wash your hands before and after dealing with larvae, especially if you will be handling another type of larvae afterwards. In between use all items that go into the tanks or contact the bugs are thoroughly cleaned and left to dry.

Small numbers: Limit a tank to smaller numbers of caterpillars with lots of available food to limit problems.

Photo credit for photos in this post goes to MOSI Outside Volunteer Patti W.