I've heard of people bleaching their milkweed and monarch eggs while raising monarchs. Should I do this?

Sanitizing containers between individuals is one of the most important steps in keeping monarchs healthy in a captive rearing environment. We do not recommend bleaching monarch eggs or milkweed plants.

It is common and encouraged to rinse milkweed leaves with water before feeding them to caterpillars. This simple step is typically sufficient to remove debris or small organisms that may come in on wild-collected leaves.

Some people attempt to bleach monarch eggs in an effort to destroy Ophryocystis elektroscirrha (OE) spores on the outside of the eggs. While this may have limited effectiveness, OE is a naturally occurring parasite in monarchs and not something that can or should be eliminated entirely from the population. Instead, the focus should be on preventing its spread in a rearing environment.

By sanitizing containers between uses and ensuring individuals are not housed together in ways that allow direct exposure, home rearers can greatly reduce the risk of inadvertently spreading OE. The goal is not to eliminate this naturally occurring parasite but to manage rearing conditions responsibly so monarchs remain as healthy as possible.

A good way to learn more about OE and to get a better sense of infection rates in the wild and in your home rearing activities is to participate in Project Monarch Health.

For more information, check out our Rearing Monarchs For Research: A Guide for Enthusiasts handout.