The Dreaded OE Spore

*Click on pictures if you want to see details*

When you begin to raise Monarch butterflies you will find that they are prone to a number of different health-related issues. One of the 'big' ones is the OE spore.

What is OE? Ophryocystis elektroscirrha is a protozoan parasite that infects the Monarch world-wide. It parasitizes the Monarch and Queen butterflies only and the spores can be found in the cuticles between the scales. With a microscope or stereoscope, some tape, and white paper, it is something that can be easily detected, and thus, controlled to an extent.

The OE parasite is transmitted from the female Monarch to her offspring. While the mama is fluttering about ovipositing (laying eggs) on the Milkweed, she is also scattering the OE spores onto the the leaves of the plants. Other Monarch larvae (caterpillars), upon hatching, begin to eat the leaves that have been 'dusted' with the spores. The spores then germinate within the caterpillar's gut, and the spores can sometimes actually be seen forming! Infected imagines (adults) eclose covered with the OE spores and the damage has been completed as once a butterfly has been infected, sadly, there is nothing that can be done.

Can you tell early on if a Monarch has been parasitized? During the larval stage, I've noticed that if a caterpillar has an appearance of being 'dirty,' then more than likely, it may have been parasitized with Oe. Click here to read more.

During the pupal stage, there may be some signs as well, such as odd-looking discolourations while the pupa is undergoing metamorphosis. For example, take a look at this chrysalis. Look at the areas that are marked by the white arrows. These are NOT normal changes occurring during metamorphosis. They appear to be somewhat 'dirty' or splotchy, right? Guess what…this butterfly eclosed with Oe. The eclosing butterfly was unable to come out of the chrysalis completely and showed signs of Oe when tested under the stereoscope. *click on the pupa to see the spots up close

Sometimes an infected Monarch may look normal. It may even eclose normally. But, it is NOT normal! Generally, these butterflies have shorter life spans and have difficulty flying. Both males and females are effected but it is the female that will transfer the spores to her offspring directly. Some infected Monarchs do not eclose from the chrysalis easily and you will find them struggling to get out of the chrysalis-do not even attempt to 'help' the butterfly as this difficulty alone will probably be THE indicator that the butterfly has been infected with OE.


Here is an example of a Monarch parasitized by the OE spore. Note how it is unable to get out of the chrysalis. The picture was taken against a wooden surface to provide a clearer picture. You can see how the butterfly is struggling. This is just one example of what the parasite can do. Sometimes a butterfly may eclose but its wings will not open up; maybe one wing is stuck in the chrysalis or the wings are simply shriveled. No amount of human intervention is going to help. The butterfly must be euthanized.

Some butterflies that do eclose are unable to fully expand their wings for some reason and will fall to the ground or, have terribly deformed wings. Others may even be smaller in size than healthy Monarchs. This parasite can cause such a wide range of problems.

How can you tell if a Monarch has been infected with the OE spore? Positive identification/testing for OE can be accomplished with a microscope/stereoscope, clear tape, and white paper. If you do not have access to these items, yet are raising a lot of them, you may want to think about investing in these items. More to come on testing...

One general but not always scientifically accurate method is to take a look at the butterfly's abdomen. If the markings on the abdomen are clear and distinct, there is a fairly good chance the butterfly has not been infected. Note how the black and white striped bands are very distinct and clear in these two pictures. This Monarch tested clear and free of OE.

Now, look closely at these next two pictures.

What can you see in the black and white markings on the abdomen of this Monarch? The white is definitely not a nice, long, thick stripe but is more mottled in colour. The black is also not as deep or rich. The abdomen even looks shrunken in comparison to the first butterfly's, which is plump and well-shaped.


This Monarch, when tested, had a LOT of OE spores and had to be euthanized.

Some may think, "I wouldn't kill a butterfly just because it had some spores on it!" Think, though, what would happen if an infected butterfly was permitted to flutter about YOUR garden. Okay, think if it was a FEMALE, she mates, and starts ovipositing several hundred eggs onto your plants. First, she is transferring the spores onto your plants each time she stops to nectar and/or oviposit. Second, she transfers the spores to her offspring. Do the math.

Is euthanizing worthwhile? You make the decision.