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!" Then again, if you do continue to let the larvae live to pupate, you will 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? Euthanize. It really is the humane and responsible thing to do.

Questions arise as to 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: A recent email questioned whether or not the spots may really indicate the existence of OE. The sender submitted these photos to Dr. Sonia Altizer who wasn't sure. I contacted Dr. Altizer myself as I have submitted specimens to her in the past, as part of her Monarch Health research project, and explained what I've found with regards to the 'dirty/spotted-looking larvae' and the resulting Monarch imago (adult) having indeed shown to be contaminated by OE. Dr. Altizer is fascinated in this 'discovery' and so I will be sending her specimens of larvae that exhibit these overt indicators for her too biopsy. She is wondering if perhaps there is a secondary cause for the lesions to occur in the larva in addition to the OE. Who knows? We may be on to something...

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