The explosion of comments and questions I receive about monarch diseases has shown they’re still a common problem for many raisers. There’s still a lot of work to be done to help everyone raise butterflies with (at least) a 90% survival rate, so let’s raise those rates!
In the past few seasons, I’ve raised hundreds of butterflies from tiny monarch egg. The only casualties I’ve experienced are from carelessness (rushing cage cleaning), and accidentally bringing in monarch predators with milkweed…mainly small spiders.
Monarch disease and death do not have to be a regular part of your raising experience.
My goal is to bring you an awe-inspiring and joyful raising experience free of monarch diseases and death….or at least bring loss down to a tolerable level, so you can experience the joys of raising, while helping the struggling monarch population.
Here are 7 monarch health issues that can be largely avoided with a few simple precautions:
1. Tachinid Flies
Tachinid flies are hard to differentiate from all the other flies in your garden just innocently pollinating the milkweed. These parasitic flies lay eggs on monarch caterpillars. The hatching maggots burrow inside the caterpillar and feed, eventually killing it.
You can typically tell your caterpillar’s been compromised when it starts to grow smaller and skinnier. Often, it will appear small if it attempts to pupate. The caterpillar often dies while forming its chrysalis. Soon after, white tachinid maggots or dark-red pupae will exit the caterpillar and fall to the ground, leaving long white strands of evidence hanging from the monarch cat or chrysalis.
- Only bring in monarch eggs for raising
- If bringing in caterpillars, try to collect caterpillars less than 4/10″ (instar 2 and smaller)
Although, I recently had maggots emerge from a small (instar 3) monarch caterpillar I was raising. It was likely parasitized as a small instar 1 or 2 caterpillar…
More info about tachinid flies here
2. Ophryocystis elektroscirrha (OE)
OE is a protozoan parasite that caterpillars ingest on milkweed. It’s spread through microscopic spores coming off the wings and bodies of adult butterflies. These protozoa multiply inside the caterpillar and can cause weakness, disfigurement, and an untimely death. You are most likely to notice symptoms of OE infection in the chrysalis or the butterfly. If you suspect your butterfly has severe OE infection, releasing it will only spread the parasite to future monarchs.
- Rinse off milkweed before serving it to caterpillars
- Don’t let butterflies emerge from their chrysalides over feeding caterpillars
- Regularly clean out frass and rinse/dry your caterpillar cage
- In warmer regions where tropical milkweed grows all year, cut plants back to 6″ twice a year so fresh healthy foliage can emerge.
Want to know more about OE? Click here
3. NPV (Nuclear Polyhedrosis Virus)
Commonly referred to as black death, your caterpillars will deflate, turn black, then liquify like something out of a horror movie! This virus can also affect chrysalides as the entire monarch chrysalis turns black.
- Use a mesh cage that allows good ventilation, allowing water to evaporate
- Vacuum up frass, wipe down and dry cage daily
- Rinse milkweed cuttings and leaves with water before serving
- Rinse cages with a weak 5-10% bleach solution at the end of every season
- Caterpillars leaking fluid or refusing to eat for more than 24 hours should be separated from the rest
- If you have sick caterpillars or chrysalides turn black, disinfect the affected cage before raising more monarchs…and switch out the milkweed supply!
4. Tainted Milkweed
It’s hard to imagine that anyone selling milkweed would treat it with pesticides, since the vast majority of milkweed customers are buying it to support monarch caterpillars and butterflies. Unfortunately, this is not always the case…
In the world of raising butterflies, tainted milkweed often rears its ugly leaves when people run out of milkweed for their caterpillars and are forced to make an emergency run to the nearest store/nursery. If you ever have to do this, make sure you are purchasing pesticide-free milkweed, or your poor caterpillars will never get the chance to finish their amazing transformation…
If your caterpillar has ingested pesticides it will often expel green vomit. If this happens, rinse the caterpillar off under a faucet, then place on a new milkweed source immediately!
Another sign of pesticide poisoning is when a caterpillar dies in the middle of forming its chrysalis. This occurs when caterpillars ingest insect growth regulators, which include organic pesticides like neem oil.
Both of these events can be disturbing and disappointing, but here’s how you can largely avoid them:
- Find local milkweed sources that grow plants without pesticides
- Find online milkweed resources that grow plants without pesticides
- Plant more milkweed in your garden to avoid having to make emergency runs
- Realize pesticide companies are not referring to caterpillars when they list their products as safe for beneficial insects
5. Trichogramma Wasps
Until recently, I thought bringing in monarch eggs assured you of hatching healthy monarch caterpillars. But there’s a new parasite in town… Trichogramma wasps lay their eggs inside of monarch eggs. If your egg turns completely dark (instead of only dark on top) monitor it for 48 hours to insure it’s not a viable monarch. If it doesn’t hatch, squeeze the egg inside the milkweed leaf and discard or little wasps will emerge in about 10 days!
- If you see a monarch female depositing eggs, collect them right away
I realize this isn’t a disease, but it’s a far too common problem that is taking precious monarchs away from us before they bloom into beautiful butterflies. Dehydrated monarchs can get stuck inside their chrysalides causing deformation and death. They may also have issues forming them.
- spritz milkweed and caterpillars daily with a spray bottle filled with water- make sure the caterpillar cage has good ventilation (i.e. a mesh cage) so the water evaporates and there isn’t condensation inside the habitat that could cause disease
- Hydration of monarchs must start at the egg stage for healthy development
Some experts and enthusiasts disagree with spritzing milkweed/caterpillars, but imagine eating food for two weeks without water…and staying healthy?!
7. Invisible Predators
These are the monarch predators that you unwittingly invite in to your cage, trapping them inside with your unsuspecting monarchs. I have done this with small spiders and stink bugs. This can be a problem when you raise on potted plants because of all the nooks and crannies where predators can easily avoid detection.
- raise monarchs on small cuttings or individual leaves so it’s easier to inspect the milkweed
- thoroughly rinse milkweed before serving it up to monarch caterpillars
- spray potted plants with water to detect spider webs
8. Bacillus thuringiensis (BT)
This naturally-occurring bacteria is used in powders and sprays to protect food crops. When ingested, it ruptures the gut lining of monarch caterpillars. The irritated caterpillar stops eating and will die within a few days.
BT can be legally used on certified organic plants.
- don’t just ask if the plant was grown organically.
- do ask if Bacillus thuringiensis (BT) was used specifically
- don’t use BT around milkweed and other host plants
What should you do if you suspect your monarch has a disease or parasite, but aren’t 100% sure?
Isolate the egg, caterpillar, chrysalis, or butterfly and monitor it for confirmation. If the monarch is kept in a separate habitat, it will not be a danger to the rest of the monarchs you are raising.
Just an ounce of prevention in raising monarch butterflies will help you avoid monarch diseases, parasites, and death, so you can grow healthy monarchs to support the butterfly population! For further info on raising healthy monarchs check out my raising guide link below:
Please Read the Comments Section below for more info about Monarch Diseases.