Why did Smithsonian entomologist Harrison Gray Dyar Jr. dig enormous tunnels in his back yard?

      Did he, as some say, construct the elaborate underground network to conduct top-secret experiments?Did the roomy passageways - complete with brick walls and six-foot plaster ceilings - provide a secret passage to a second family across town?

      Or did the turn-of-the-century scientist simply find digging in the dirt relaxing, as he himself explained?

      Dyar died in 1929, after suffering a stroke at his desk. His legend survives.

      So do the tunnels themselves, which fan out as far as 200 feet behind his old Dupont Circle home, though they're now sealed with concrete. But they never went anyplace anyway.

      "I've been working for 19 years as the historian of the Smithsonian, and Dyar seems to me to be the quintessential Smithsonian eccentric," said Pamela M. Henson, who began digging up facts about Dyar 10 years ago.

      She was joined in her work by Marc E. Epstein, a modern-day Smithsonian entomologist who works every day beneath a photograph of Dyar.

      Henson and Epstein recently published Dyar's story in "American Entomologist" magazine.

      Dyar came to the old United States National Museum in 1897, and still worked there in 1924, when a truck accidentally broke through into one of his creations. But by then Dyar had moved across town, and his involvement with the underground network wasn't apparent.

      The newspapers had a field day, with stories of World War I intrigue.

      The Washington Post ran a banner headline: "Old Tunnel Here Believed To Have Been Used By Teuton War Spies and Bootleggers!" It even invented a tale of the secret underground laboratory of a certain Dr. Otto von Golph.

      Dyar must have enjoyed the hubbub. He didn't come forward immediately to clear up the mystery.

      When he finally did tell his story to the Washington Star, he said his tunnel-digging habit began around 1905, when he dug a hollyhock bed for Zella, his first wife.

      "When I was down perhaps 6 or 7 feet, surrounded only by the damp brown walls of old Mother Earth, I was seized by an undeniable fancy to keep on going," Dyar said.

      Henson describes Dyar as an "irascible curmudgeon," obsessed with moths and mosquitoes and rarely known to smile. He was well respected, and an entomological law bears his name.

      But his private life provoked gossip. He had divorced his wife, with whom he'd had two children, and married an outspoken Washington intellectual, Wellesca Pollock Allen.

      The divorce was in 1916, the second marriage in 1921.

      It all seems straightforward on the surface.

      But then how does one explain the popular tale of Dyar's secret family, of his two wives and two sets of children, who supposedly met each other by chance one day in school?