I’m a sucker for weird antennae, so this plant bug was an obvious choice for this week’s column. Heterotoma planicornis seems like a gregarious enough character to have a common name, but it doesn’t, nor is there much information about it in general.
In fact, I couldn’t find an answer to the most obvious question: Why does this bug have such outlandish antennae? It waved them about in all kinds of rabbit-like patterns. Was it detecting something? Warning me off? Using a semaphore code?
Planicornis is Latin for “flat horn,” so I suppose we could call it the flat horn bug. These little Miridae family bugs are omnivores, and this one kept returning to an aphid that I presume it was snacking on. They also eat plant juices, and are associated with a variety of trees and forbs, including stinging nettle.
These are very small critters, measuring 4.5 to 5.5 millimeters long. Female Heterotoma planicornis are larger, but without two of them together, it’s impossible to judge this one’s sex. Flat Horn Bugs have one generation per year, and they overwinter as eggs. They live up and down the U.S. West Coast and in a few states farther east.
I’d actually seen a nymph of this species before at Mount Pisgah, near the main entrance on the path by the river. I’ll include a photo here but because it’s even smaller than the adult, it’s not in great focus. Nymphs also eat plants as well as mites, aphids and spiders, and their antennae are equally super-sized.
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Better image of a nymph: https://petehillmansnaturephotography.wordpress.com/2017/06/25/heterotoma-planicornis/. Accessed 8/3/22.
Research paper on the abundance of species that use stinging nettle as a host: https://www.jstor.org/stable/2404726. Accessed 8/3/22.