It’s been said that an ecologist is someone who puts up birdfeeders in hopes of seeing hawks. The same principle applies to milkweed for monarchs; what you often get is wasps.
A little background here. We’ve had the pots of milkweed out for the butterflies, we’ve seen a few stop by, my roommate even spotted a few eggs. Yet the milkweeds remained unmunched beyond tiny holes, and every possibility of a caterpillar just… disappeared.
Meanwhile, we kept spotting wasps. Whom I suspect are the culprits.
While classic high school biology books present monarch butterflies as poisonous so birds learn not to eat them, and other butterflies mimic the monarchs to go unmolested, said books neglect to mention that monarchs have other predators beyond higher vertebrates. The caterpillars, in particular, while just as toxic as the butterflies, have no shortage of predators that have their ways of getting around said toxin. Most of it’s in the skin, after all, and if you can avoid eating that, you’re good. Wasps are pretty darn good at that.
So what do you do if you want to provide good monarch habitat?
I see three possible courses of action. You can accept the predation, you can kill the wasps, or you can protect the caterpillars.
The first option may be preferred by a lot of people trying to keep critters as wild as possible. After all, if predators weed out the sick and undesirable, maybe you don’t want those caterpillars to survive. It’s a valid argument. On the other hand, if the wasps build a nest right over where you have the milkweeds, they are going to hunt out every last caterpillar, sick or not. They take easy prey – and easy can also mean just “close by enough to find with a little more hunting”.
Which may lead directly to the second option: kill the wasps. Again, valid depending on your situation; nobody wants a wasp nest directly overhead. Some people are as deathly allergic to them as those allergic to bees, in which case I say take what measures you need to defend yourself. Ouch. But again, on the other hand, caterpillars are wasp food; they may keep luring in more wasps from other places, no matter how you spray. And wasps as predators do keep down other insects that are not so desirable.
We, personally, are taking the third option. We have a screened-in porch, we moved the milkweed there, and the current crop of tiny caterpillars are chewing away. When they get to the chrysalis stage and within a few days of hatching out, we’ll move the pots back outside; wasps tend not to bother them then. So the adult monarchs can take their chances just like any other adults. We’re only sheltering them to that point. You know, like they do in a lot of other wildlife rescue programs; get them ready to survive on their own, then it’s on them.
But we can only do that because we have a screened area, and only a couple of pots to worry about. More than that would be too much for us to handle.
…Which is something to remember any time you want to “change the world”. Take on only what you can handle. You’re a lot more likely to follow through, and get good results!