Disease

Preventing disease is essential to raising monarchs successfully. And we don't want to threaten the wild population by releasing diseased butterflies.

Here's a link to various diseases that occur in captivity.

For us, the most concerning disease is a parasite nicknamed "O.E." after its scientific name Ophyrocystis elektroscirrha.  Since this disease can be spread by spores clinging to eggs, I test all my laying female monarchs for the disease.  Any infected adults in my breeding tent are released (if lightly infected) or euthanized.  So, you can be assured that your eggs are free from OE.  However, it is still possible for caterpillars to become infected by ingesting spores on the milkweed you feed them.

Any adult monarch is potentially infected with OE and may be shedding thousands of spores.  So, anything like a mesh cube that has touched an adult butterfly should be sterilized before being used for caterpillars.

If you suspect a caterpillar is diseased in any way, you should immediately separate it from the others and observe it.  But be aware that caterpillars normally rest (often leaving their food) for up to 24 hours each time before and after they shed their skins.  So just being sluggish or inactive for up to 24 hours isn't a sign of disease.

One sign of pesticide poisoning is for caterpillars to stop eating and become sluggish.  But othewise, they look normal.  They are not discolored (black) as with some diseases, nor do they show movements inside (parasitic larvae eating them from the inside) or threads attached (where tachinid larvae emerged).  If you present them good food from another source, and they resume eating--that's a good sign they had mild pesticide poisoning.

Many monarch scientists raise caterpillars individually, each in their own container, to reduce the spread of disease.  But we have found that raising them individually has the disadvantage of requiring more equipment and is more labor-intensive.  Go here for an account of our new method and why we changed from raising individually.

Using the new method of raising groups of caterpillars on stems of milkweed, I've had almost no disease, despite raising hundreds of caterpillars together.  I screen the egg-laying females for OE disease.  If you keep the caterpillars indoors, that eliminates the small tachinid flies that parasitize caterpillars.  If you soak used equipment in 5% bleach and wash* the milkweed food under cold running water (and inspect for spiders), that will do the rest.

Remember, don't allow a container (like a mesh cube) that has held butterflies to come into contact with caterpillars without sterilizing it first.  If any of your butterflies emerge infected with the OE parasite, they will be covered with OE spores that can later infect caterpillars.

Checklist for preventing disease and predation

1. Wash all your equipment at the end of the season with a 5% bleach solution, rinse it, and label it as sterilized.  
2. OE: Never put caterpillars in a container or mesh cube which has held adult monarchs unless you sterilize it first.  If you hold a butterfly, wash hands before handling a caterpillar.
3. Keep clean conditions, and don't allow frass to remain wet.
4. Rinse milkweed food (to eliminate OE spores)?  Some people do.  Although I don't, I still have very little disease.
5. Keep soil away from caterpillars.  Soil harbors some monarch diseases.  For example, don't use a potted milkweed plant to feed caterpillars.
6. Raise caterpillars indoors or a screened area to eliminate tachinid flies or wasps.
7. Protect eggs or small caterpillars from spiders by inspecting milkweed food for predators and by creating "moats" (a flooded saucer) to keep spiders inside the house from reaching your monarchs.
8. Use milkweed from a known, reliable source, away from an agricultural or pesticide-treated areas.

Bleach Solution for disinfecting

Use ordinary chlorox-style bleach, sodium hypochlorite.  Mix 1 part bleach to 19 parts water to make a 5% solution.  Soak any of the containers in this solution for 10 min. or more.  Rinse thoroughly.

*Monarch Joint Venture does not feel washing milkweed food is necessary.  I do not wash the food when I raise caterpillars, and I have seen almost no disease.