For years, my husband and I have nurtured milkweed in the lost corners of our yard. “Remember the Monarchs!” we chant, as we carefully work around the tall milk-sap plants.

While Monarch butterflies eat nectar from a bunch of different plants, the caterpillars eat only milkweed as they grow. The milky sap of Milkweeds is toxic to most animals, but not to Monarchs. In fact, in’s all that Monarch caterpillars eat. What’s more, the Monarch caterpillars incorporate the toxins into their own bodies, and use it as a chemical deterrent against predators.

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In spite of this incredibly cool adaptation, Monarch populations have been declining for decades — between 50-90% loss since 1991. Habitat loss has been a major problem in the United States, especially with the introduction of herbicide-resistant corn and soybeans so that herbicides can be sprayed on them to get rid of milkweed growing between the rows. In Mexico, where they overwinter in just a few select spots in upland forests, they are vulnerable to illegal logging operations, cold snaps and hurricanes. Car strikes are also a surprising big killer of Monarchs in Mexico — up to 200,000 killed in just two locations near their over-wintering spots! Monarch Butterfly Migration

There’s not a lot we can do to alleviate these problems. But we can grow milkweed to give as many Monarchs as possible a good start in life. Through the years, we’d been rewarded with a few Monarch butterflies. But no caterpillars.

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And lately, we’ve become aware that the decision to grow milkweed is itself a trade-off — native milkweed is attractive to European honeybees, but it can be a deadly trap for them, too. Bees and Butterflies.

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Bees are already having a hard time from colony collapse disorder, where the bees just disappear. After years of research, nobody knows why. It’s a major problem with honey bees, one that’s not getting better. I was beginning to feel that if the Monarchs weren’t using the milkweed, we should rip out the it and replace it with something more bee-friendly.

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And then, for a real treat …

… my husband found two tiny yellow, white and black caterpillars happily gnawing on our milkweed.

Maybe the milkweed will stay after all.