Partnering to conserve the monarch butterfly migration

Question and Answer

What should I do if I suspect a monarch I'm raising has OE or some other disease?

Similarly to cold and flu season, disease in monarchs can spread rapidly between individuals. It is rare to find monarch caterpillars in high densities in the wild. Perhaps this is a mechanism to reduce the spread of disease, among other things. Here are a few rules of thumb for how to handle diseased individuals and to make sure that monarchs you bring in from the wild to raise stay healthy (although, disease does happen naturally, so isn't always preventable!): 

  • Never let adults emerge in the same container that caterpillars are eating. Caterpillars cannot spread OE to one another because the OE parasite spores are within the gut of the caterpillar. In the adult butterfly form, however, the spores reside on the outside of the insect's body and drop/rub off onto various surfaces, including the milkweed leaves that caterpillars eat. Once a caterpillar consumes OE spores that dropped off the adult, it becomes infected. Thus, it is always good practice to keep hungry caterpillars in separate containers. 
  • Raise monarchs in individual containers to minimize close contact and spread of disease. It is easier to keep track of and isolate sick or diseased-looking individuals. Viral or bacterial disease in monarchs is extremely detrimental and will spread very quickly to all of the individuals you are raising if appropriate precautions are not followed. 
  • While individual containers help reduce transfer of disease from one container to another, it is important to consider how you are handling them as well. If an individual appears to be sick, handle it last. Wash your hands or change your gloves regularly. Minimize how much you handle adults and larvae; the less you disturb them, the better. It is important to make sure they have fresh milkweed and clean containers, but try to avoid too much handling of the monarch. 
  • Clean your containers regularly with a 20% bleach solution. At a minimum, bleach containers before introducing a new monarch. 
  • When a caterpillar is showing signs that clearly indicate it is sick, it is very rare for the individual to recover. To maintain the health of the others you are raising, separate any sick individuals from others that appear healthy, and in extreme cases, it may be best to euthanize it. 
  • Do not dispose of dead individuals back into your garden to prevent spreading the disease in the wild environment. We recommend freezing dead specimens, and then disposing of them in your trash. 

For more information on rearing responsibly, here is our Rearing Monarchs Responsibly handout!

Back to Frequently Asked Questions