Reproduced with permission from the Monarch Butterfly Parasites Webpage,

University of Georgia,

The answer to this question depends on how heavily infected the monarch is. Many OE infections, especially of eastern North American monarchs, are ‘mild’ cases, and the infected adult monarch will look nearly identical to a healthy adult. Mildly infected adults will also act normal, so it is usually impossible to know if they are infected without testing them using the methods described below. Unfortunately for those of us that rear monarchs in captivity, these mildly infected adults can spread their spores around their cages and rearing containers just as well as heavily infected ones, which is why it is essential to test all adult monarchs upon eclosion, and remove any infected ones immediately. Also, since there is no way to ‘cure’ adult monarchs once infected, they must be destroyed. Releasing them to the wild will only spread the parasites further and you will risk contaminating your favorite local milkweed patch.

Below are some pictures of various OE infected monarchs. The monarch in the bottom right image is indeed infected, but appears otherwise normal.


How to test for parasites in your monarchs 

Things you will need for the test:

Disposable gloves
Clear scotch tape
Blank index cards
1 pair of fine forceps
A standard light microscope or a handheld 30X mini-scope


Step 1. Put on your gloves!

Step 2. Cut out a 1cm square piece of scotch tape.


Step 3. Position the adult monarch in your fingers with its abdomen exposed.


Step 4. Using your forceps, gently place the sticky side of the piece of tape to the abdomen of the monarch. Press down so that it wraps around and sticks to the sides of the abdomen.


Step 5. Gently peel the tape off and stick it to the index card. You will remove some scales in the process, but don’t worry, it will not harm the monarch.


Finish by labelling the tape sample on the spore card with the identity (we use a number) of the monarch. Continue these steps until you have sampled all of your monarchs. In the end, your index cards should look something like this:

The numbers on the bottom of each sample refer to the number of the butterfly in our lab, and the numbers above refer to the parasite ‘spore load’ on each monarch (we use a 0-5 scaling system). Notice that one monarch from these samples was infected and was given a 5 score (heaviest infection category).

Step 6. To determine if your monarchs are infected with OE, look at each tape sample under your microscope at 30-40X. If any monarch is infected with OE its tape sample should look something like this:

The red arrows indicate the parasite spores in this image. The big objects are the monarch scales. The spores look like tiny lemon-shaped objects, often clumped together. Under a good scope they’ll have a reddish tinge. This monarch would be considered heavily infected. Keep in mind that many infections are mild so you may only see 20 spores in the entire tape sample. If you do not find any parasite spores then the monarch is clean! If you do find an infected individual, it should be isolated from your other monarchs and then destroyed. Also, change your gloves after handling any infected monarch so you will not spread the spores around your workspace.

Note: If you have access to a light microscope, you can use a variation on this method by placing the tape sample on a microscope slide instead of an index card.

*Remember to dispose of your gloves and wipe down your work surface when you finish, especially if you found (and handled) an infected monarch!