Sometime around September 25, 1924 the streets of Washington D.C.’s Dupont Circle district opened up and swallowed a truck. I imagine that was quite a shock for the truck driver who suddenly found himself in the literal dark underbelly of his nation’s capital. It was also a surprise to nearly everyone in the city, especially when it was discovered that the reason for the sinkhole was an elaborate series of tunnels dug beneath the area.

Speculation quickly suggested nefarious plots involving spy rings and bootlegger operations, neither of which turned out to be true. To the best of anyone’s knowledge, the tunnels didn’t lead to a great Masonic treasure, either.

The explanation finally came from a former resident of the neighborhood, Harrison Dyar, a fifty-eight-year-old, independently wealthy and highly respected entomologist who spent most of his career at the Smithsonian Institution. There he was the custodian of the Lepidoptera. In case you aren’t up on your bugs, that’s the order of insects that includes butterflies and moths.

If moths do happen to be your thing, then Dyar’s name might be familiar to you. He’s the rock star entomologist behind Dyar’s Law, which is a ratio that can be used to identify larval stages based on insect head width, a fact I’m sure you already knew. He’s also the inspiration for the genus of moth once known as Dyaria. That name has since been changed to Coenodomus, which is harder to pronounce, but is also much easier to say with a straight face.

But that’s not all Dyar is known for because, when he was done looking at insects all day, he also had an unusual hobby. For years, the man spent an enormous amount of his free time digging tunnels that snaked from his home through the ground beneath Washington D.C. When asked why he did this, he replied that he did it for exercise.

His children and their friends played in the tunnels, some of which were reinforced with concrete, lined with ceramic tiles, and included ladders, archways, decorative animal sculptures, and strings of electric lights. The whole thing allegedly started one day when Dyar dug a garden for one of his wives (because there’s more than moths to this historical figure) and then he just kept digging until, a decade and a half later, a truck fell through the streets of Washington D.C. Oops.

Dyar’s tunnels are all filled in or bricked off today, but of course rumors abound that there are plenty of underground tunnels and bunkers throughout the city. Some claims are substantiated. A few such spaces are even open to the public.

Others remain little more than whispers, though I doubt anyone would be surprised to find that Washington D.C. has its fair share of dark, cavernous secrets and an unstable underbelly created by the custodians of all manner of Dyaria.