Late summer is the time to find what the British call Ladybird Flies. If you disregard the head and wings of this fly, it looks remarkably like a lady beetle, right down to the white patches behind the round little beetle’s eyes, which are represented by the coverings of the fly’s halteres, or vestigial wings.
These cleverly-costumed flies are in the Gymnosoma genus. Gymno- means naked (as in gymnasium) and -soma means body (as in somatic). Compared to other flies in the family, which have names like Bristle Fly, these are indeed clean-shaven creatures.
While the resemblance to a ladybug probably helps the fly (the beetles are notoriously bad tasting, and predators would steer clear), this is hardly an innocent nectar-sipper. All flies in the Tachinidae family are parasitoids. That means they not only use another creature as food, but that creature loses its life in the process.
Gymnosoma flies lay an egg on or near adult stink bugs. The larva makes its way inside the bug, and eats the host tissue as it grows. When it’s ready to make a pupa, the fly leaves the bug host, probably without even a ‘thank you,’ and finishes its life cycle in the soil.
Some lady beetle mimic flies have different markings on the abdomen, like this third photo. I’m guessing it’s a different species, but citizen science sites say that it’s difficult to identify these flies to species without dissecting them and looking through a microscope.
One research paper I read says that Gymnosoma have super-sensory perception (not their term) to locate stink bugs. The study found that both male and female flies are attracted to pheromones the stink bugs produce, which is helpful, if you’re looking for a place for your kids to grow up.
You’ll see Gymnosoma flies on flowers into October. Look on wild carrots, a.k.a. Queen Anne’s Lace, at Mount Pisgah.
Stay curious!
See more of Karen’s work here.
Sources:
Research paper on Gymnosoma awareness of stink bug pheromone: https://www.sciencedirect.com/science/article/abs/pii/S1049964411001253. Accessed 9/2/25.
Abstract on “respiratory funnels” that these flies produce so they can breathe while inside a stink bug: https://pubmed.ncbi.nlm.nih.gov/38629304/. Accessed 9/2/25.
All photos by Karen Richards.