Meet the Stealthiest Assassin Bug in the United States

The unique and secretive species has been living among us unrecognized for a century

Get a good look at Sinea incognita, a newly recognized species of assassin bug. (Entomological Society of America)
smithsonian.com

A hidden group of assassins has been lurking undetected around the midwestern and eastern U.S. for years. The formidable killers ambush their victims by stabbing them with hollow, blade-like instruments and sucking out the liquids inside—not unlike the horrific brain bug from Starship Troopers. Despite their fearsome nature and conspicuous killing tactics, scientific authorities have only just now identified the predators as Sinea incognita, a newly recognized species of assassin bug.

The wheels for S. incognita’s discovery were put in motion in 2006, when J.E. McPherson at Southern Illinois University sent a newly designed assassin bug key—a step-by-step pictorial identification guide—to a handful of colleagues around the country. All of the scientists were in accordance with McPherson’s identification of three assassin bug species except for one. Scott Bundy, an entomologist at New Mexico State University, found that his specimens for the species S. complexa didn’t quite match the ones McPherson sent over.

S. complexa and nine other Sinea species were described back in 1900, and the original descriptions of that assassin bug family have remained more or less intact since then. But Bundy noticed that his S. complexa specimens had slightly narrower front femora—the insect equivalent to a bicep—than the ones McPherson sent over.

Bundy alerted McPherson to his misgivings and mailed him a few specimens collected from out west. Upon closer examination, McPherson found that Bundy’s insects were indeed S. complexa, but that his seemed to be something else entirely. The physical differences are subtle but noticeable, McPherson and co-author Imtiaz Ahmad describe today in the Annals of the Entomological Society of America

The leg of S. incognita (top) is bulkier than those of related species S. complexa (middle) and S. integra (bottom). Entomological Society of America

A close examination revealed that the eastern species, S. incognita, possesses femora shaped a bit like Popeye the Sailor Man’s forearm, whereas S. complexa’s femora are punier, resembling a baseball bat. The new species also has more menacing-looking spines than the other Sinea members.

Researchers previously thought that S. complexa roved across the U.S. and parts of Mexico, but scouring museum and university collections revealed that its range is actually confined to the west and southwest. The newly revealed assassin bug can be found from Maryland to Georgia, and west to Kansas and Texas. Given that the bug has been hiding in plain sight for all these years, McPherson decided to honor its master-of-disguise antics. As he explained in a release: “I have named this species S. incognita to indicate that it has remained hidden for over 100 years as S. complexa, to which it is closely related.” 

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