A Growing List of Monarch Killers
The same misinformation we embraced last century continues to mislead new generations through shows like Wild Kratts: Voyage of the Butterflies. In this episode, a spider cuts a monarch from its web, refusing to eat the milkweed-laced butterfly…essentially spinning science into science fiction!
While I can’t argue the show was entertaining, I’ve already heard this misinformation repeated from several of its young fans.
While nature’s truth may not always be pretty, it must be told if monarch enthusiasts across North America want to effectively increase the struggling monarch population.
Here’s what you need to know…
Common Monarch Predators and How to Stop Them
ALL Monarch Predators
Plant placement can reduce predator traffic. Monarch eggs and caterpillars on single milkweed plants often go undetected…so do plants in partial shade.
Many species of ants will feed on both monarch eggs and caterpillars. They also feed on other butterfly caterpillars:
What’s worse, is ants share this strange symbiotic relationship where they protect milkweed-destroying aphids in exchange for their sweet secretions! Nature is nothing if not strange…
In our northern climate, we have several ant species in our garden and I’m sure they eat some monarch eggs and caterpillars. However, they have not proven to be a nuisance so we leave them alone, as we do with many insects that butterfly gardeners consider pests.
If your garden pests are innocent until proven guilty, a healthy ecosystem should develop that can support both monarchs and their predators.
And as always, you always have the option of bringing in a few eggs or small caterpillars to save them from the surprisingly long list of monarch predators…
But, if their numbers start getting out of control:
Ant Solution 1
Mix 1 Tbsp. of powdered sugar with 1 part baking soda. The powdered sugar attracts them, and the baking soda disrupts their digestive tracks, eventually killing them. Place the mixture in jar lids near the plants they are invading.
Ant Solution 2
outdoor liquid ant baits– these weatherproof baits by terro are stuck into the ground so they’ll stay in place during stormy weather. Ant-killing borax is the main ingredient. These pre-mixed baits are cheap, convenient…and they work!
If you know of other effective solutions for keeping ants at bay in the garden, please post in the comment section below…
Ant Solution 3
MBG Community member Roberta C. and others have reported using coffee grounds to repel ants in their gardens:
“Use coffee grounds, recycled works fine, not decaf, in your dirt around your milkweed. Ants depend on their scent trail to survive and make it home, there’s something in coffee grounds that disrupts their trail or scent so they avoid coffee grounds. Grams used it in her flower beds and veggie garden.”
You can also pour the grounds on their anthill to encourage them to move their base of operations…
Tip: rewet the grounds every few days to enhance the coffee smell
Mantids are skilled hunters that eat a variety of insects including monarchs. Mantids are sometimes used as biological pest control. The nymphs eat aphids and leafhoppers, but the adults will go after larger prey:
Mantis Solution 1
A prime example of why you should avoid biological pest control…there are usually unintended consequences!
Mantis Solution 2
Relocate monstrous mantids to less butterfly-friendly plants.
If you raise monarch butterflies, there is a great lesson to be learned from this disturbing video:
note: yellow jackets aren’t the only predatory wasp attacking monarchs. Paper wasps are the worst monarch predator in our northern garden, on constant patrol for monarch caterpillars.
Wasps are an issue for monarchs across the globe, from the US to New Zealand.
If you raise monarchs, they need at least 3 hours to dry their wings before they are released. If you want to learn more about how to safely raise and release monarchs, check out my raising resources page.
If you’ve read other articles on this blog, you know I’m a proponent of nurturing a healthy ecosystem which includes monarchs and their predators.
Wasps are always welcome in our garden as beneficial pollinators, but unfortunately, their children have to eat…caterpillars.
If you watched the video above, you might have have vowed to keep your garden wasp-free. I’m here to tell you that’s not possible or advisable.
Remember, one monarch lays hundreds of eggs so predators are a necessary evil to maintain a healthy ecosystem in your garden…
However, that doesn’t mean you need to host wasp nests on your property. We removed potter wasp nests from the bottom of a common milkweed leaf.
We also had a paper wasp nest on our house, conveniently built right above one of our milkweed patches.
Wasp Solution 1
If this happens to you, you can sacrifice most of your monarchs or you can take down the nest when it’s dark, cold, or raining…do this early in the season before the population explodes.
You should be able to knock down the nest with the handle of a long broom, but if you can’t, or they come back, you’ll have to consider more permanent solutions…
Wasp Solution 2
A community member suggested these non-toxic W.H.Y. (wasp, hornet, yellowjacket) traps that are supposed to be very effective for trapping these relentless predators without harming the environment:
The next solution is potentially more dangerous to the both the environment…and to you! So please, proceed with caution…
Wasp Solution 3
This is one of the only times I’m on board with using pesticides in the garden, but please read the label carefully and try to keep the spraying directly on the nest:
Last season we sprayed an underground yellow jacket nest in our raised beds. We sprayed early morning during a light rain, and I never saw another wasp emerge from the nest.
Wasp Solution 4
A good way to deter wasps is by placing 5 Gallon Paint Strainers or Mosquito Netting over your milkweed. You can use tomato cages for extra support. This will keep them from snatching up your poor, unsuspecting caterpillars. This idea works best for potted milkweed plants.
Spiders are the kings and queens of camouflage. They are usually hidden from sight and will feed on your small caterpillars at night.
Also, if you raise monarchs on potted plants or stem cuttings with buds/flowers, it’s easy to unknowingly invite spiders into your raising cage.
If you consider that spiders feast on most of the other pests in your garden, I’d suggest keeping them around.
If you have a limited milkweed supply, consider removing any spider webs that have been formed on your milkweed plants. Spiders can also be carefully relocated to nearby areas. You could cut off a small piece of occupied plant, and carry the spider outside the milky way. 🕷
You can’t (and shouldn’t) save all monarchs if you want to maintain a healthy ecosystem. However, bringing a few indoors to raise can help boost their low survival rate…less than 5% outdoors!
If you decide to bring a few in, feed the caterpillars stem cuttings without flowers/buds or serve single leaves.
Discover the system I use to raise monarchs with a 95% survival rate in the updated 2019 Raising Monarchs Guide
UNEXPECTED Monarch Predator
If you raise monarch butterflies, make sure you don’t place monarch eggs too close together.
After a newborn caterpillar hatches, its first meal will be the nutrition-laced egg shell. If other eggs are in the vicinity, the hungry little caterpillar may wander over to an unhatched neighbor for seconds.
The same is true when placing newborn caterpillars with large ones. If they are competing for the same milkweed leaves, the large caterpillar could eat the competition for lunch…or dinner.
In the hatchery, I space eggs out so newborns won’t find unhatched siblings. When caterpillars hatch, move remaining eggs to other leaves.
To prevent cannabalism of small caterpillars, make sure you’re raising them in a large enough caterpillar cage, with plenty of milkweed available.
More Monarch Predators List
- Assassin bugs feast on monarch caterpillars
- Birds (Black-backed orioles and black-headed grosbeaks are common predators for butterflies overwintering in Mexico.)
- Chalcid Wasps (monarch chrysalis parasite)
- Mice will eat chrysalides
- Spined Soldier Bug- Predatory Stink Bugs
- Tachinid flies (monarch caterpillar parasite)
- trichogramma wasps (monarch egg parasite)
More Monarch Predators Coming Soon!