Common Monarch Ailments 101

Many people have been asking the question, “What's wrong with my Monarch caterpillar/egg/chrysalis?”

This is a list of the MOST common problems that the Monarch Rearer may encounter and how you can either avoid your Monarch from being infected or avoid the infection from spreading  to your other caterpillars. Hopefully these tips and indicators can help you raise healthier Monarchs in the future!

Warning: Some photos may seem graphic or unpleasant. ​

Black Death

What is Black Death?
As the name suggests, this is a fatal and very unpleasant ailment for the Monarch. Black Death is a general yet appropriate term used to describe the effects of two different infections. Pseudomonas is a bacteria that thrives in moist environments and Nuclear polyhedrosis virus (NPV) is a virus.

How to tell if your Monarch has Black Death:
Your caterpillar may be fine one day and the next start to  become lethargic,  start to deflate, refuse to eat and start to turn a darker color. Sometimes their chrysalises will turn dark brown or they pupate and then liquefy into a black goo. This can be a traumatic experience for the Monarch Rearer but once your caterpillar has contracted Black Death, it is nearly impossible to save them and the best thing to do is remove it immediately from the cage and disinfect anything it may have touched in order to prevent it from spreading to other caterpilalrs. 

Note: NPV causes the caterpillar to climb to a high spot, hang in an l or inverted V shape, and die. The caterpillar then liquefies inside and when the skin of the caterpillars splits open, the black goo will send millions of virus particles on its surroundings. The smell is very pungent. If a caterpillar lies at the bottom of a rearing container (instead of crawling higher in the container) and dies either firm or mushy, it is not infected with NPV. 

How to prevent Black Death

• The Pseudomonas bacteria like moist, warm environments so try to keep your butterfly cage dry, well-ventilated and out of direct sunlight. 
• Clean the frass (butterfly poop) everyday and disinfect the tray before putting it back in the cage.
• Gently rinse and dry milkweed before putting into your cage.
• If you see any signs of an unhealthy caterpillars or chrysallises (read indicators above), isolate it from the other caterpillars.

O.E. (Ophryocystis elektroscirrha)

What is OE?
OE is a protozoan parasite that is spread through microscopic spores coming off the wings and bodies of adult butterflies. These spores are packed in between scales on the Monarch's body and when it lays eggs, often attaches to the egg shell. Because OE is a parasite, it relies on a living host and will generally not kill Monarchs but will lead to weakness, disfigurement, and lethargy. Eventually it may die from sheer exhaustion.

How to tell if your Monarch has OE:
You won't be able to tell if a Monarch has OE until it's in the pupal or adult stage. Infected chrysalises won’t have a uniform green color. You can check your chrysalis closely to make sure it's dark spots are mirrored on both sides. Heavily infected Monarchs may not emerge or if they do they may be deformed or too weak to hold on.

How to prevent OE:

• Gentry rinse off milkweed with water before giving it to your caterpillars
• Clean out frass and disinfect the cage everyday
• In warmer regions where tropical milkweed grows all year, cut plants back to 6″ twice a year so fresh healthy foliage can emerge.

Tachinid Flies

What are Tachinid Flies?
Tachinid flies can be difficult to differentiate from other flies in your garden. However, if you look closely, you will see that they are hairy and have huge red eyes.

How tell if your Monarch was infected by a Tachinid Fly:
This is one of the easiest Monarch infections to identify. They lay eggs on monarch caterpillars and once hatched, the maggots will bore into the caterpillar and feed on them while they are still living. You can generally tell if your caterpillar has been infected if it suddenly gets much skinnier and will sometimes die while attempting to form it’s chrysalis.  These flies also lay eggs inside chrysalises. After it’s host has died, the maggots will emerge, leaving tell-tale white strands of silk hanging from the caterpillar or chrysalis.

How to prevent Tachinid Flies:

• Closely inspect monarch caterpillars before bringing them inside and choose ones that are second Instar or even smaller.
• Keep a close eye on your caterpillars and eggs

Pesticide Poisoning

​Sadly, it occurs quite often where nurseries treat their milkweed with pesticides or roadsides/fields are sprayed where you collected milkweed/caterpillars unknowingly.

How to tell if your Monarch has come into contact with Tainted Milkweed:
​ If your caterpillar has ingested pesticides it will often expel green vomit. 
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How to avoid this from happening:

• If you notice your caterpillar vomit, gently rinse off the caterpillar under water and put it on a different (untreated) milkweed plant immediately. 
• Plant a large amount of milkweed in your garden so you don’t have to buy milkweed elsewhere
• If you have to buy milkweed from a nursery, ask if they have been treated with ANY pesticides
•  If there isn’t a local provider close to you, check online for untreated milkweed seeds .
• Proceed with caution even when companies list their products as safe for beneficial insects. Even organic products can be unsafe for caterpillars such as Neem Oil and Diatomaceous Earth

Trichogramma Wasps

​What are Trichogramma Wasps?
They are tiny parasitic wasps that inject a single egg into the eggs of the pest. After consuming the contents of its host egg, a new adult wasp will emerge within 10 days.

How to tell if your Monarch has come into contact with Trichogramma Wasps:
If your egg turns completely dark keep an eye on it for the next couple of days to make sure a Monarch doesn’t hatch. If it doesn’t hatch, squeeze the egg inside of the leaf and dispose of the leaf.

How to avoid:

• When gathering Monarch eggs, try to get them inside right away

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​Chalcid Wasps

What are Chalcid Wasps?
This is another tiny, parasitic wasp that waits for the perfect moment to attack your beloved caterpillar. It will approach when the caterpillar is in it’s vulnerable “J” stage and wait for it to form a chrysalis. Then, right afterwards, it lays hundreds of its eggs in the soft chrysalis.
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How to tell if your Monarch has been infected by Chalcid Wasps:
Look for small black dots where it appears they have deposited their eggs.

​How to avoid:

• When gathering Monarch eggs, try to get them inside right away
• Use fine mesh enclosures to raise monarchs. Larger holes in laundry baskets will allow these impossibly small wasps access to your monarchs during this most-vulnerable time.
• If raising outdoors, do not leave your habitat open for long periods while cleaning and check the cage for flying insects before closing

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Anal Prolapse

​When this occurs, the caterpillar’s rectum protrudes from its anus, leaving a bright green ball at the end of your caterpillar. It’s not known what causes this, but it’s always fatal to the caterpillar.

Resources

https://monarchbutterflygarden.net/common-monarch-diseases-prevention/
http://butterflyfarms.org/monarch-predators-parasites-and-diseases/
https://monarchjointventure.org/resources/faq/common-monarch-problems
https://butterfly-fun-facts.com/oe-ophryocystis-elektroscirrha-monarch-butterfly/