What Are the Orange-and-Black Bugs Swarming My Milkweed? Identifying the Large Milkweed Bug

By late summer, milkweed plants are covered in life. Among the most eye-catching residents are clusters of bright orange-and-black insects massed on the seed pods, often in a jumble of different sizes. Gardeners who planted milkweed specifically to help monarchs frequently panic at the sight — but these are large milkweed bugs, a harmless native species that has been part of the milkweed community for as long as the plant has existed. Knowing what they are takes the alarm out of the picture.

How to Identify the Large Milkweed Bug

The large milkweed bug (Oncopeltus fasciatus) is a slender, oval insect about half to three-quarters of an inch long. Its bold pattern is the giveaway:

• An orange-red body crossed by a distinct solid black band across the middle of the back
• Two black triangles — one pointing forward, one pointing back — separated by that central black bar, plus a black band across the shoulders
• Clear, dark wing tips that lie flat over the back
• A long, straw-like beak tucked under the head, used to pierce and drink from milkweed seeds

You will usually see a whole range of sizes together. The smaller, wingless, rounder, more solidly orange individuals are nymphs — the immature stages — clustered right on the pods with the winged adults. That mix of sizes on a single milkweed plant is itself a strong clue you are looking at milkweed bugs.

Milkweed Bug or Boxelder Bug?

The most common mix-up is with the boxelder bug, another orange (or red) and black insect. The quickest tells are pattern and location. A boxelder bug is mostly black with thin red-orange lines outlining its wings and three fine stripes behind the head, and you find it on and around boxelder, maple, and ash trees or gathering on sunny walls. A large milkweed bug is mostly orange with big black patches and that bold central black band, and it lives on milkweed. As a rule of thumb: bright bug on a milkweed pod = milkweed bug; darker striped bug on a tree trunk or house siding = boxelder bug.

Are They Harmful to Monarchs or the Plant?

Large milkweed bugs feed on milkweed seeds and plant juices, not on monarch caterpillars or eggs — they are not predators. On an established milkweed patch they cause little real harm; at most they reduce the number of viable seeds a plant produces, which matters if you are trying to collect seed but not if you simply want to support pollinators. Like monarchs, they absorb bitter toxins from the plant, which is exactly why they wear the same warning colors. There is generally no need to control them, and spraying milkweed risks harming the very monarchs you planted it for.

Seeing a cluster of orange-and-black bugs on your milkweed and want to be sure they are friends, not foes? Take a photo and let Spotter identify the insect, so you know whether you are looking at harmless milkweed bugs or something worth a second look.