When should I release the Monarchs?

monarch butterfly
Photo credit: Lynn Ketchum

I am planning to be able to release Monarch butterflies, but need to know when the proper time for doing this in Salem. Can you find this information for me?

- Marion County, Oregon

Thank you for your interesting question that raises some additional questions interesting. Many people are concerned with the dramatic decline in monarch numbers, and a natural response is to try to help them out. If your intent is to help boost the natural monarch populations, those that you release probably won't do that. In fact there is the potential to do more harm than good. The longer monarchs (or any animal species) are bred in captivity, the more adapted they become to that environment and the less adapted they are to the "wild". So there is the possibility yours may not survive to reproduce. If they do breed with wild monarchs, that will introduce those less desirable captive traits into the wild populations. Another downside is that many captive bred monarchs are infected with pathogens, especially Ophyrocystis elektroscirrha (OE) and that could then be introduced into an otherwise healthy population. Also the original homeland of your monarchs is an important consideration. Those from east of the Rocky Mountains are a distinct population from those found in the western USA. The eastern types are the ones that famously overwinter in Mexico but are not compatible with the western types. The western types winter in southern California.

As I am sure you know, all monarchs depend on milkweed plants for food for their caterpillars and those or other flowering plants for nectar for the adults to feed on. Working in your community to help increase the abundance of native milkweeds would help their populations more than releasing captive bred butterflies. Just remember that milkweeds are considered by many (especially farmers) to be weeds. In the right setting, they can be a wonderful plant to have and can provide the right habitat for monarchs as they return to the Salem area in mid to late June.

If you are interested in learning more about the distribution of monarchs and milkweeds in the west, please see the Western Monarch Milkweed Mapper and the information on its webpage. You can also learn more about Oregon milkweeds from the Xerces Society's article.

Stuart Reitz
Professor/Crops Agent
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