In September 2008 a coworker described encountering a swarm of hundreds of small black and red beetles. From the description I assumed it was a gang of ladybugs/ladybird beetles. But she shared a picture taken that cancelled my assumption. Although similar in appearance to ladybugs, these were undeniably a different creature.
In September 2008 a coworker described encountering a swarm of hundreds of small black and red beetles. From the description I assumed it was a gang of ladybugs/ladybird beetles. But she shared a picture taken that cancelled my assumption. Although similar in appearance to ladybugs, these were undeniably a different creature.
Nymph form of the white-margined burrowing bug. This may look like a swarm, but they’re harmless vegetarians.
Faced with a difficult insect identification question, I did what I normally do in this circumstance—I handed it off to my significant other. While not an entomologist, she is outstandingly tenacious at such tasks. A short time later she told me they were white-margined burrowing bug nymphs. Having never heard of these critters before, I looked them up so I could see what the adults look like. I passed the identification on to my coworker, and that was the end of it. Or so I thought.
Adult white-margined burrowing bug. Photo credit: Patrick Alexander
Eight years later, I encountered a swarm of hundreds (maybe thousands) of "small black and red beetles" on my own. They were in a forest opening maybe a tenth of an acre in size. The soil was very rich with organic material, moist, and dominated by spotted jewelweed and stinging nettle.
I was struck by some déjà vu but couldn't recall anything further about them in the field. I watched them for a few minutes, noting their actions and taking some photos.
This time back in the office I decided to learn about them, not just what they were. Very quickly, I learned information that I don't expect to forget when I see them again, even if it isn't until 2024 (if this 8 year pattern holds true).
The white-margined burrowing bug is not well-known. At 5 millimeters in length, it’s easy to miss. Most people learn about this insect the way that my coworker and I did—by encountering groups of the red and black nymphs gathered together. They’re true bugs that are found in fields, woodlands, lawns, and gardens. They feed primarily on plants in the mint family, but they’re not considered a nuisance insect and almost never cause any significant damage.
A most exciting and unusual thing about this bug is that the mother cares for her young. In the insect world, this rarely happens. The female adult will dig a burrow in the soil and lay over a hundred eggs. She guards the nest while waiting for her eggs to hatch. After her eggs hatch, the mother brings food back to her young in the form of mint seeds. The maternal care continues for several days while the young are helpless. Once you see the nymphs above ground, they are no longer helpless and can find their own food.
The white-margined burrowing bug is rare in the insect world in that the mother beetle cares for her young, carrying them around and bringing them food. Photo credit: Patrick Alexander
