Raising Monarch Butterflies

I am a biologist by training, so I like to slip in a biology lesson when I can. Raising monarch butterflies offers a unique opportunity for an insect life cycle learning opportunity. We have been growing swan plants for a couple years now. This year, I think we have finally reached critical mass of 14 plants, so hopefully I won’t need to run to the garden centre to get additional plants this year.

Monarch butterflies self-introduced to Aotearoa New Zealand by “island hopping” from North America in the 1870s. Monarch butterflies can only breed by providing their caterpillars with a diet of introduced swan plants. So it is a case of plant them and the butterflies will come.

Things to consider

Population control: It is not to fun to watch caterpillars starve, and this may be a harsher life lesson than you want to teach the kids. However, you may not want to keep buying more and more plants, as I have done in past years. The best way to deal with this problem is to limit the number of eggs that get laid on the plants. You can do this by wiping off excess eggs from the bottom of leaves (you will always miss some), and/or bringing the plants inside or covering them in mesh once there are a few eggs on them. It is better to raise a few butterflies, than a large number of caterpillars, that run out of food before they can pupate.

Emergency caterpillar food: Larger caterpillars (ones just about to pupate) can eat pumpkin, cucumber or courgette/zucchini for a day or two. However these vegetables do not contain the chemicals necessary for a pupa to develop correctly into a butterfly. Even feeding these to large caterpillars will reduce the proportion of pupa that are able to emerge as butterflies, so this is a last resort.

Keeping butterflies in the garden: While caterpillars can only really eat swan plants, adult butterflies can eat from a variety of flowers. You may consider planting these in conjunction with swan plants to encourage new butterflies to stay in your garden, once they emerge.

What the kids can do

Swan plants: I am not sure about other countries, but in Aotearoa New Zealand, most garden centres stock insecticide-free swan plants during monarch butterfly breeding season (spring-summer), you can also buy seeds to raise you own plants. Kids can help grow the plants and plant them.

Monitoring plants: At the start of the season, we check the plants for the first eggs, then little baby caterpillars. Later on we check for chrysalises and then watch for them to hatch.