Milkweed bugs


Milkweed bugs (actually, nymphs of various stages) feeding on milkweed pods.

If you grow milkweed (Asclepias species), you will also grow milkweed aphids, milkweed bugs, milkweed beetles, and, if you’re lucky, monarch butterflies. The past few years I’ve been much more likely to see the aphids and the bugs than the butterflies, but they’re all good.

All milkweeds contain cardiac glycosides, poisonous chemicals that are deadly to most creatures. All the insects that feed on milkweeds are able to do so without being poisoned because they can digest these deadly substances. Evolution is a game of one-upmanship. Asclepias plants evolve a poison that insects can’t eat, so insects evolve a way to metabolize that poison. Those protected insects benefit: they themselves become poisonous to predators. They flaunt this advantage with bright red or orange colors so their prey recognizes their defense mechanism and leaves them alone.Then other insects evolve similar coloration, but without the defense mechanism–they’re free-loading on evolution. It’s all really, really cool.

Reliably in late summer or early fall, some of the many milkweed plants in my garden are infested with milkweed aphids and bugs. The adult bugs are a little less than an inch long and very handsome. Here’s a picture:

Large Milkweed Bug, Oncopeltus fasciatus

Large Milkweed Bug, Oncopeltus fasciatus (R. Bessin, 2001)

Typically you see the adults mating on the milkweed pods, and about three weeks later you see a scene like the one at the top of this post: lots and lots of nymphs all over the pods. They have piercing mouth parts, which they use to feed on the seeds within the pods. They destroy the pods they feed on, meaning that perhaps 10 percent of the seed in my garden is lost. There’s still plenty to collect, and the bugs don’t harm the plants in the slightest. And they’re so very, very cool looking!


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