What is wrong with my monarch?
What is wrong with my monarch?
There are many diseases that affect monarchs, so it is usually impossible to determine with complete certainty which disease caused a monarch’s death. A monarch that looks ill or otherwise abnormal could have been infected with a virus, bacteria, parasite, genetic problem, or fungus.
- Shriveled up:
- With silk-like threads coming from body:
- Tachinid flies (parasitized)
- Parasitized by wasps
- Disease
- With silk-like threads coming from body:
- Turned Black:
- Black death (common diseases are Pseudomonas bacteria or Nuclear Polyhedrosis VirusNPV)
- Larva stopped eating and turned pale:
- Bacterial infection
- Molting: The larva may appear a bit less vibrant while they are shedding their old exoskeleton. They are fragile during this stage, so it is best to not touch them until they are done molting.
- Green “goo” came out of the larva:
- Ate contaminated milkweed, the pesticides most likely caused it to vomit/expel the milkweed.
- The monarch larva was squished or injured.
- Bright green ball at the end of the caterpillar:
- Anal Prolapse (this is always fatal)
- Failed to emerge properly:
- OE (use Project Monarch Health’s OE testing kit)
- Disease
- Genetics
- Unsuccessful parasitism
- Did not finish creating a chrysalis:
- Genetics
- Disease
- They may die in the middle of their chrysalis formation, or right before they are about to pupate (hang in “J-shape”).
- Chrysalis had dark spotting on it:
- OE
- Disease
- Bruising from being handled
- Parasitism
- If the entire chrysalis has darkening pigment, that likely indicates that the monarch will be eclosing from its chrysalis soon.
- Chrysalis turned brown or black with holes in it:
- Parasitized
- Parasitism by tachinid flies is common. This is especially obvious if there are silk-like threads hanging from the chrysalis. The fly pupa look like small brown pellets.
- Resource on tachnid parasitism: https://monarchjointventure.org/blog/citizen-science-brings-monarch-butterfly-parasitoids-to-light
- Parasitism by tachinid flies is common. This is especially obvious if there are silk-like threads hanging from the chrysalis. The fly pupa look like small brown pellets.
- If parasitized by wasps (Pteromalus cassotis, a species of chalcid wasps), there will be small black dots on the chrysalis where the eggs were deposited. About 2-3 weeks after parasitism, the wasp offspring will chew a hole in the pupa and emerge from inside.
- Parasitized