Milkweed Bug Nymphs
On September 15, 2024, one of the seed pods on the milkweed plants beside our back door was absolutely covered with these small, bright-orange insects. At first I thought they were some type of aphid, but (a) they don’t have the little cornicle projections on the abdomen that are characteristic of aphids, and (b) they were burrowing into the seed-pod, which is not very aphid-like behavior.
It turns out that they are actually the nymphs of one of the milkweed bugs in the genus Lygaeus. While they have piercing-sucking mouthparts like aphids do, they specialize in sucking juices out of seeds, and so these are going inside the pod to get to the developing milkweed seeds. It is hard to identify them to species when they are just nymphs, as all of the nymphs of this genus look about the same, but since we have found Lygaeus kalmii in our milkweed before, this is most likely more of the same.
I mainly wanted to get these pictures because they were there in a large group, and not individuals like I’ve seen before. They were variable in size, but not so much in appearance, which makes me think they were all on the same molting stage. It’s just that the little ones had probably just molted,
while the biggest ones were just getting ready to molt again.
I am still amused by the fact that practically all of the insects that eat milkweed are not only orange, but are that particular shade of orange (except for monarch butterfly caterpillars, which are yellow. But even those turn this shade of orange when they become butterflies). I kind of suspect that milkweed leaves probably contain carotenes that are that specific shade of orange, and so the various milkweed-feeders just co-opt the carotene from the milkweed to use as a warning pigment. And, of course, the reason they have use for a warning pigment is that they also all use the cardiac glycosides from milkweed latex as a defensive chemicals to make themselves taste bad.
Of course, all of them using this same shade of orange also means that they help each other out. If a bird eats any of these orange insect and then gets violently ill, then it will avoid all the other orange insects as well rather than having to sample the butterfly, and the beetle, and the bug, and the aphid, and the other beetle, and. . . .