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Monarch Butterfly Diseases

​Monarch Caterpillars seem to be the hardest to raise to the butterfly stage.  They are prone to diseases that other butterflies do not have or have less of.  It does get frustrating spending time raising the caterpillar and in the end to have an unexpected death.  We have to remember that in the wild only 10 caterpillars out of 100 will make it to the adult stage.  When we get involved and raise them on our own, the chances change to 90 caterpillars out of 100.  BUT that also depends upon where you live.  Down here in Florida and the southern states, we have a higher rate of mortality.  Our growing period is longer and hence, more diseases occur here.  I thought I would provide some links that may help you out.  The two Monarch diseases are OE and NPV - Ophryocystis elektroscirrha and Nuclear polyhedrosis virus.  I have come across these diseases in Wisconsin but it is more prominent in Florida.  See the below websites for more information.  This also applies to the butterflies in the Monarch family, such as the Queen and others.



What is OE?

Black Death​​

The Prevalence of OE Infections ​​

The ABCs of Lepidopteran Disease

Sterilization for Disease Control


Milkweed Diseases/Pests

Monarchs cannot survive without milkweed; their caterpillars only eat milkweed plants (Asclepias spp.), and monarch butterflies need milkweed to lay their eggs. We fill our gardens with milkweeds to support the Monarch and their habitats.  ​​​​We buy milkweed from nurseries or big box stores and find they have been sprayed with pesticides and realize we cannot raise Monarchs on these plants.  We then go through the process of trying to grow from seeds.  Then we find some of the seeds need a cold treatment to stimulate winter.  After we go through all that, we are greeted with aphids, wasps, leaf wilt and other diseases.  Here are some links to help you with that:

Common Milkweed Pests​​

Milkweed Problems

Parasites and Natural Enemies​​

There comes a time when one has to decide to cut down their milkweed plants even though the season has not ended. By cutting it down, it does help to eliminate disease.  The plants will grow back fuller and healthy.  There is also concern that the milkweed will overwinter growing and multiplying the chances of disease if we do not have a killing frost which most years does not happen in Florida, at least where I live.  The longer the plants grow in our gardens, the chances for disease and milkweed problems increase.  Some butterfly experts suggest the cutting of milkweed down to the ground at the end of September.  The plants will recover.  This also is a way to cut back on the chances of the OE virus spreading.  Right now in August my plants look like palm trees, meaning no leaves on the bottom of the plant and only a small  few on top.  No seeds are being produced, thus this plant is not really health​​y.  The milkweed that has been mentioned to be causing problems is the Tropical milkweed and I have read about this on numerous sites/blogs.  In many nurseries this is the common milkweed we find to purchase.  So frustrating!

The main predator in my garden seems to be the wasp.  I have seen them patroling and collecting small caterpillars for their young.  This year I have seen them attack a full grown Monarch caterpillar and eat it.  The caterpillar is double the size of the wasp.  I wouldn't have believed it if I hadn't seen it.  ​​​

How do the caterpillars and butterflies have any chance in this world of ours?

Advanced Caterpillar and Butterfly Care Information​​


Monarch Butterfly
​and Milkweed Diseases