OE on Caterpillars

Look carefully at your developing Monarch larvae (caterpillars). Do you see any unusual dirt-like spots? If so, chances are likely that your caterpillars have ingested the OE spore. This is the parasite that affects Monarch and Queen butterflies and has a deleterious effect upon their lives. Check the pictures below (click on each to enlarge for more details). Can you see the spots? OE parasitization causes many problems for developing

Look at the antennae on this caterpillar. Notice anything unusual?

What do you see on these two?

How about these two?

Click on this picture to see a close-up of the things that would include the dirt-like or 'dirty' spots, mottled or uneven striping, misshapen antennae, …

Now, what to do with the caterpillars…Chances are, you are thinking, "I can't just kill the babies! That would be inhumane!" If that's the case, isolate! You can keep an eye on the lifecycle that way.

Then again, if you do continue to let the unusual-looking larvae live to pupate, you may end up with a pupa that may or may not eclose. If you've ever had a butterfly that struggled to get out of the chrysalis, then there's a good chance that butterfly had been parasitized by the OE spores. Even if you helped the butterfly get out of the chrysalis, that butterfly's chance of living a full and healthy life would be slim. OR, maybe the butterfly does eclose. You may end up with a malformed butterfly. The butterfly looks normal but is so infected with OE that it spreads the parasites as it flies through your Milkweed, dropping the spores as it nectars OR passes the spores along to its offspring. Monarchs that have been parasitized with OE have been shown to live a shorter lifespan, have greater difficulty with flying longer distances, and pass the spores to their offspring.

What do you think would be best then? If it was up to me, I'd say euthanize. I do separate larvae based on appearance and from my own personal experiences, have found that the 'different' ones rarely do not become healthy butterflies. This may be a case here in Southern California…I don't know.

If you do elect to euthanize, the question is how to euthanize. There are a variety of methods of doing this.

  • Killing jar (Dip a cotton ball into some nail polish remover containing acetone and place this into a jar with a lid. Place the larva into the jar and seal the lid tightly for one hour.)
  • Freezing (put in a baggy then put in your freezer for at least one day, then put into the trash)
  • Squishing/smashing (put larva in a baggy or paper towel then squish)
There are a number of other methods as well but these three are probably the most common. The most important thing to remember is that YOU are helping to keep the Monarch population healthy by not releasing diseased specimens into the environment.

Note: I received a recent email (9/3/14)  from Dr. Sonia Altizer at the University of Georgia. She says that in all of her research, she did not think that different colors indicated Oe but that larvae should be isolated and observed. Some will be fine, others may not make it. Again, in my personal experiences, I have found that the mottled ones do not make it so I euthanize. It's up to you to make your own decisions!

A special Thank You to Leigh Hayes for the heads-up on noticing the little spots/dots on Monarch larvae and its possible connection/correlation to OE.

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some of the adorable clip art found on this website is used with the express written permission of D.J. Inkers