OE (Ophryocystis elektroscirrha) is a protozoan parasite that infects butterflies in the Danaus species group, those that host on milkweed. In the US, Monarch (Danaus plexippus), Queen (Danaus gilippus), and Soldier (Danaus eresimus) butterflies are affected by OE.

OE can weaken caterpillars and cripple adult butterflies. Only rarely will OE kill a caterpillar, chrysalis, or butterfly. A parasite that is 100% dependent upon its host for its own life cannot kill the host or it will kill itself. OE is a master at keeping itself going through life cycle after life cycle in nature. That being said, there are times when the caterpillar is so infected with the parasite that it cannot live.

In spite of the fact that a large percentage of wild Monarchs have OE, we encourage everyone to take every precaution to, as much as possible, prevent OE in any Monarchs they raise. We will share here, on this page, how to limit this parasite.

According to a University of Georgia study, in the wild, in the western US, about 30% of all wild Monarch butterflies have HEAVY OE spore loads. In the eastern US, less than 8% of Monarch butterflies have a HEAVY spore load. In the southern tip of Florida, where Monarchs fly and lay eggs all year, more than 70% have HEAVY OE. Experts estimate that nearly 100% of wild Monarchs in the Miami/Dade area of Florida are infected with OE, from mild to heavy infection. If OE was super deadly in the wild, the southern tip of Florida would not continue to have a large population of Monarch butterflies. That being said, even the loss of one Monarch to OE is one too many, especially in these times of dwindling numbers in the United States and Canada.

OE Life Cycle:

OE spores are found on the outside of adult Monarch butterflies. They are not attached to the butterfly. They are packed on the outside of its body, in between and on the scales. One butterfly scale may have hundreds and hundreds of spores on it.

As the adult lays eggs, scales and spores often stick to the egg shell.  One scale can have over 100 OE spores on it.  This is a Monarch egg with one scale on it.

Monarch butterfly scale on a Monarch butterfly egg

In addition, as Monarch butterflies fly about, spores fall off like glitter falls off Christmas cards. When we receive a Christmas card with glitter, the more we move it about, the more glitter lands on the floor, tables, our hands, and other items. Glitter from the cards stays around the house for weeks and months. It’s the same with OE spores. Spores fall off butterflies as they fly over and about milkweed plants. As adult butterflies land on the plants to drink nectar or lay eggs, they leave spores sticking to things like glitter stays on your hands when you hold a glittery Christmas card.  This photo shows scales without spores and scales with spores.

Monarch butterfly scales without and with OE spores
Monarch butterfly scales without and with OE spores

The caterpillar is the only stage that can ‘get’ OE. The spore may be on its egg shell or on a leaf that it eats. Once the caterpillar eats a microscopic spore, it has become infected with OE. The spore breaks open in the caterpillar’s gut. The parasites then move to just under the hypoderm (skin) and duplicate asexually, each one duplicating many times. During this time, the caterpillar is weakened by the parasite.

When the caterpillar pupates, the parasites begin to duplicate sexually. About three or four days before the adult butterfly emerges, the parasites begin forming into spores.

When the adult butterfly emerges, the spores are on the outside of its body. Remember, the parasite was at the hypoderm. This means that when it is maturing as a chrysalis, the parasite is between the maturing butterfly inside the chrysalis and the chrysalis shell. As soon as it emerges, even before it fills its wings and flies, the spores are ready to come off to be accidentally eaten by caterpillars. They are ready to be spread by the adult butterfly and eaten by caterpillars to continue the OE parasite life cycle.


Caterpillars contract the disease but cannot give the disease to another caterpillar. If you have six caterpillars with OE and six without OE and raise them in the same container, the end result will be six butterflies with OE and six butterflies without OE. (Unless you are feeding them milkweed leaves with OE spores on the leaves.)

Chrysalises have OE just under the cuticle (skin/hypoderm). It cannot contract or spread OE. The spores are inside the chrysalis.

Adult butterflies that had OE as a caterpillar will be CONTAMINATED with OE. OE is no longer living inside it. It has been weakened by the parasites and may not be as strong or live as long as butterflies that were not infected with the parasite.

A butterfly that has OE spores on its body may have only a few spores or it may have many hundreds of thousands of spores. If a caterpillar eats one spore shortly before it pupates, it will have only a few spores. If it ate quite a few spores as a hatchling caterpillar, it will be covered with spores as an adult.

Adult butterflies (that eat milkweed as caterpillars) should never be emerged over milkweed or caterpillars.  If the adults have OE, the caterpillars will get OE from spores that fall from the adults.

 Eggs and OE:

If you bring eggs in from your garden, you can disinfect the eggs before they hatch.  Disinfecting the eggs won’t kill 100% of the spores but it will kill enough to make it more than worth your time.

Pathologists recommend using bleach to disinfect eggs.  If you have bad reactions to bleach, a more expensive hospital disinfectant can be used. Pathologists often say, “Bleach is your best friend”.

Check out our video on YouTube that shows how we disinfect eggs.

Bleach will ‘go bad’ if it is left in sunlight. Store your bleach indoors. It is recommended that you make a fresh batch of bleach solution each time you disinfect eggs, leaves, or chrysalises.

Many people are nervous about washing butterfly eggs with a bleach solution. There is a chance that a few eggs may not live. But if you live in an area where OE is prevalent, you will save more from OE infection than you’ll lose from washing the eggs in the solution.

It is OK for eggs to be under water! Remember that they are normally outdoors in rain and storms. They can sit in a drop of water for long periods of time after a rainstorm.

We have a video on YouTube that shows how we disinfect eggs at our farm. Click here to view that video in a new window. If you would like to disinfect eggs and are uncomfortable with the idea, practice first with leaves that do not have eggs attached. If you’re still uncomfortable with the idea but OE is prevalent in your area, practice several times until you are comfortable with the process. You can practice “how to disinfect eggs” without using eggs.

Remember that bleach will leave spots where it splashes on clothes. We recommend that you either wear a protective apron or wear your old clothes or both. Disposable gloves are available in any pharmacy.

Bleach dissolves the cement that holds stones in rings. Be sure to remove or protect your gloves before using bleach in your home or to disinfect eggs.


If you wish to experiment with the process before actually bleaching eggs, try the process on about 20 grains of rice several times. You will become more comfortable with experience. Once you are comfortable, disinfect some eggs and wait for them to hatch. Once they’ve hatched, you’ll be proud that you are being proactive where OE is concerned.

Raising Caterpillars and OE:

In a closed rearing operation, where OE infected butterflies are laying eggs and their offspring are raised and allowed to pair and lay eggs, generation after generation, the spore load can become so intense it will begin to kill butterflies, chrysalises, and eventually can reach the point where it can kill caterpillars. If eggs are disinfected and only OE free offspring used for egg production, within two generations the facility can be free of OE infected butterflies.

Caterpillars with OE have signs and symptoms exactly the same as most butterfly diseases. Caterpillars may be totally normal in actions and appearance. Some may be slightly duskier in color. Some will be sluggish. Some will be smaller than those without OE because they simply don’t feel up to eating as much. But every one of these signs and symptoms could be the sign or symptom of a deadly disease. If a caterpillar acts or looks funny, isolate it! If it has OE, it wouldn’t have given it to another caterpillar, but if it has most of the diseases caterpillars contract, you could be saving every other caterpillar in the rearing container. Do not EVER assume your caterpillar has OE. Assume it has a horrific disease and raise it separately. You may be ‘wasting’ effort if it has OE or is not diseased but it is always best to use extra precaution. OE is a parasite that doesn’t negatively affect most of the caterpillars it infects. Diseases are often deadly, spreading quickly throughout a rearing container and through the other containers in the house.

OE cannot be spread from one caterpillar to another. A caterpillar must eat a spore to become infected with OE. If one assumes a caterpillar has OE and leaves it with other caterpillars, if it has OE, it will not cause a problem. If it has a disease, the disease can spread to other caterpillars. Remember, OE is NOT a disease. It is a parasite. Assuming it has OE is a quick method to spread disease to other caterpillars, if it does not have OE. Please, never assume. Always isolate any that have signs or symptoms of OE or disease.

If you bring a caterpillar in from your garden, you have no control over OE that may have infected it before you brought the caterpillar indoors. It may already have OE and there is nothing you can do to stop it. The most you can do is prevent a caterpillar from eating spores once it is in your possession. You should 1) wash your hands before cutting milkweed to feed to your caterpillars, 2) disinfect the milkweed before you feed it to the caterpillars, and 3) wash your hands before you touch a caterpillar or its disinfected food.

For those who keep special butterflies for egg production, it is important that they take the time to work diligently to keep OE out of their rearing operation. All egg-laying adults should be checked for OE spores. All milkweed should ideally be raised in an area where wild butterflies cannot reach the plants to spread spores.  If that is not possible, the plant leaves should be disinfected before they are fed to caterpillars. The leaves can be disinfected by soaking them in the same solution as we recommend for the eggs but they should leave the leaves under water for 5 minutes. After their bleach water soak, rinse the leaves several times and pat them dry before feeding them to their caterpillars. Wet leaves are not healthy for them.

Milkweed Leaves and OE:

OE infected adult butterflies spread OE spores like Christmas Cards spread glitter. If Monarch or Queen butterflies can fly to and land on your milkweed plants, there is a chance the plants have spores on the leaves. You can disinfect the leaves just as you disinfect eggs, except leave the leaves under the bleach solution for five minutes before rinsing well. Pat the leaves dry before feeding them to your caterpillars.

Chrysalises and OE:

Monarch chrysalises with a developing heavy OE spore load will show uneven dark patches through the chrysalis shell a day or two before the butterfly emerges. You can learn more about OE in chrysalises by clicking on this sentence. Remember: once the caterpillar has OE, there isn’t anything you can do to stop it. Many people recommend that people euthanize Monarch chrysalises and adults that have OE. Others recommend euthanizing only those that have heavy OE spore loads. We recommend that you conduct online research and make your own decision.

When handling and/or disinfecting chrysalises, remember that the cremaster of one can puncture another chrysalis, causing death or deformity. If transporting chrysalises, it is best to wrap each chrysalis separately with a square of toilet tissue or piece of paper towel.


If you suspect a chrysalis has OE, check the dark patches carefully. Are the dark patches mirror image of themselves, left side and right side of the chrysalis? If so, it is not OE. Those dark areas are the maturing butterfly. When there is a dark spot or splotch on one side that isn’t mirrored on the other side, it is time to suspect OE.


Although we recommend disinfecting chrysalises exactly the same way you disinfect eggs, disinfecting them will not remove OE spores from inside them. Disinfecting chrysalises simply cleans the outside of the chrysalis. If spores from an emerged butterfly contaminated a chrysalis, disinfecting it will kill the spores on the outside. If the butterfly inside does not have OE, it could pick up spores from the chrysalis shell when it emerges. Again, disinfecting chrysalises will NOT kill spores inside the chrysalis. If the butterfly inside is infected with OE, nothing can be done to help it. Nothing. Period.

Adults and OE:

Some adult butterflies that are heavily contaminated with OE spores will be unable to emerge from their chrysalises. They often crack the chrysalis open, emerge partway, and then die while struggling to finish emerging. Some emerge fine but cannot expand their wings properly. Their wings dry crumpled, leaving them unable to fly. Some look normal but are weak. When that happens, most people assume that the butterfly has OE. This is a dangerous assumption. If the emerging butterfly does not have OE, it may have a disease or other issue causing the problem. Simple dehydration from being indoors can cause the exact same scenario. If you don’t know for sure whether the butterfly has OE and you assume it is OE, you are leaving the door open for it to continue happening again and again.

Most adult butterflies with OE look normal, fly normal, lay eggs normal, and seem to live a totally normal life.

Adult butterflies can be checked for OE by placing a piece of CLEAR tape firmly to its abdomen, removing the tape (which now has scales on it), placing the tape on a microscope slide, and looking for OE spores. Removal of these scales will not harm the butterfly. They naturally wear off as they age. We’re just hurrying the process of losing a few scales a bit. To learn more about checking adult Monarch and Queen butterflies for OE, please click on this sentence.



If you wish to know if a butterfly has OE and do not have a microscope, please feel free to mail the tape to me with your email address enclosed. Use CLEAR tape (not invisible tape) and fold it back upon itself. Make sure you have a good sampling of scales from its abdomen. If you wish to be totally anonymous, simply do not place your return address on or in the envelope. Instead, choose a number or code. We will check the tape and if you have an email address enclosed, we will email you the result.   Mail the tape to: OE Check, Shady Oak Butterfly Farm, 12876 SW CR 231, Brooker, FL 32622.

At Shady Oak, we only keep OE butterflies when we are doing tests and experiments to learn more. They are not released into nature. Because we are careful about our breeding stock, we only have OE infected butterflies when we buy plants from nurseries (that grow them outdoors where butterflies can touch them) and take the caterpillars in to raise them. These are kept separate from our line of OE free healthy breeding stock.

Do My Monarch Butterflies Have OE? Ophryocystis elektroscirrha

“I don’t have a microscope. How can I check to determine if my Monarch butterflies have OE?”

Many Monarch butterflies that had a bad OE infection cannot emerge from their chrysalises. Many will emerge but will be unable to pump their wings full and flat. This in itself is not proof of an OE issue.

Other issues can cause this same problem for an adult Monarch butterfly. Please don’t assume that a butterfly that has crumpled wings or cannot emerge has OE. By assuming that they have OE, you may be overlooking a worse problem that can be easily corrected.

This can also happen from something as simple as low humidity or a slightly deformed/damaged chrysalis.

These first two photos are of Monarch butterflies that were raised from wild caterpillars taken from a plant nursery. Although it wasn’t fun to see the OE infected chrysalises and adult butterflies, it did give us a perfect opportunity to take photos of them.

To check for OE, simply take a piece of CLEAR tape (NOT ‘invisible’ tape) and touch it GENTLY but FIRMLY to the abdomen of a Monarch, Queen, or Soldier butterfly. After you tape the adult butterfly, simply fold the tape over and stick it to itself. This prevents other things from sticking to the tape. Simply insert it into an envelope and mail it to us.

You can mail the tape to us at the farm. If you would like us to check your tape, please include your email address and we will send the result to you and you alone. We never share names of or information about anyone who sends us tape.
OE Check
Shady Oak Butterfly Farm
12876 SW CR 231
Brooker, FL 32622

(Photo to the left) If you would like, you can first do this simple test. It will show a positive result only if the butterfly is heavily covered with spores. If a Monarch or Queen has only a light spore load, it won’t show if you are using this method. After firmly (but gently) pressing the tape to the abdomen to the butterfly, press the tape firmly to a clear piece of glass. A window pane, drinking glass, or other item works well. Remove the tape and hold it up to the light or place a white piece of paper behind it. If spores were on the adult butterfly, some will stick to the glass. The top slide has tape (with scales on it) on the slide. The bottom slide is the SAME slide with the tape removed. All the black color on the lower slide photo are OE spores. There are no scales on that slide in that photo. Some of the butterflies had so many spores that they stuck to the slide. It is immediately evident that those butterflies had a super heavy OE spore load. If you do not see spores after you remove the tape, you can fold it back over itself and mail the tape to us to check. (Instructions below)

Spores are easily visible through a 100x microscope. We do not encourage you to purchase a toy microscope. As stated above, if you do not have a microscope, please mail the tape to us if you would like to know if it has OE.

Two photos to the left show why we insist on clear tape. ‘Invisible’ tape is wonderful for taping paper and wrapping presents. ‘Invisible’ tape distorts anything seen through it. The same butterfly was used for both photos; clear tape and invisible tape.

With invisible tape, you cannot tell what is on the tape. You cannot differentiate between spores, dust, pollen, and other items.

OE spores are much smaller than Monarch or Queen butterfly scales. Over one hundred spores can fit on one scale.

If you do not see spores on your tape, it does not mean that your butterfly doesn’t have spores on the outside of its body. It does mean that it isn’t heavily contaminated with spores. It may have had a light infection. 

If you see something on the tape/slide through a microscope and it is NOT a perfect football shape, it is not OE. Pollen, dust, and other items will stick to a butterfly.

The ‘dust’ photo to the left was taken after I pressed the tape to the top of a door frame and next taped an adult butterfly. Dust is not perfectly football shaped.

If a butterfly is heavily infected with OE, you can often determine that fact before it emerges as an adult butterfly.

A day or two before the wings become visible through the chrysalis shell, black spots or shapes may show through it. If the black shapes/spots are perfect mirror images, left and right side, they aren’t spores. If they are not perfect mirror images, they are spores.

Spores are UNDER the chrysalis cuticle (skin). If the cuticle has black spots that appear to the on the outer layer, chances are that they are light damage from oxidation, rough handling, or other damage.