PASADENA, CALIFORNIA — I hadn’t thought much about the relationship between fruit flies and Predator drones before visiting the California Institute of Technology, but Caltech, which boasts more than 30 Nobel laureates, teaches many things, not least about the fast-growing field of robotics and war.

Fruit flies, as I learned from a graduate student, use optic flow to navigate their environment. Optic flow is the apparent motion of the landscape relative to the insect as it flies through it. When the insect gets closer to an object, that object appears to get larger; the expansion in the optic flow field triggers a collision avoidance response in the fly, which veers away from the expanding object.

“The insect eye is not, and does not need to be, high resolution to make this computation, so it follows that low resolution sensors can be employed in robotics and serve the same purpose,” she told me.

Call this bio-mechanics — biologically inspired engineering principles. It’s a booming field. You’ll find fruit flies tethered to pins under microscopes in a virtual arena with the aim of developing simplified command algorithms that will tell a robot sensor how to mimic the insect for navigation. The feedback loop for the robot is simple: If an object is expanding at a certain rate, that equals proximity, so turn away!

The U.S. military is interested in such experiments because robotics is its hot new thing. The loss of more than 5,000 U.S. military personnel in Iraq and Afghanistan since 2001 has concentrated minds on putting robots rather than flesh and blood in harm’s way.

When the United States went into Iraq in 2003, it had a handful of pilotless planes, or drones; it now has over 7,000. The invasion force had no unmanned ground vehicles; the U.S. armed forces now employ more than 12,000. One is called the PackBot and is made by iRobot, manufacturers of the popular robot vacuum cleaner called the Roomba.

Since taking office, President Obama has shown a quiet predilection for drone warfare. He’s been vacuuming up targets. There are two programs in operation: a publicly acknowledged military one in Iraq and Afghanistan and a covert C.I.A. program targeting terror suspects in countries including Pakistan.

As Jane Mayer notes in a groundbreaking recent piece in The New Yorker, “The intelligence agency declines to provide any information to the public about where it operates, how it selects targets, who is in charge, or how many people have been killed.”

According to a just-completed study by the New America Foundation, quoted in Mayer’s piece, Obama has authorized as many drone strikes in Pakistan in nine and a half months as George W. Bush did in his last three years in office — at least 41 C.I.A. missile strikes, or about one a week, that may have killed more than 500 people.

The dead have included high-value targets like Osama bin Laden’s oldest son and Baitullah Mehsud, the Taliban leader in Pakistan — as well as bystanders. Circling drones have struck panic. But as Mayer notes, “The embrace of the Predator program has occurred with remarkably little public discussion, given that it represents a radically new and geographically unbounded use of state-sanctioned lethal force.”

These are targeted international killings, no less real, and indeed more insidious, for their video-game aspect. The thing about robotic warfare is you can watch people get vaporized on a screen in Langley, Virginia, and then drive home for dinner with the kids. The very phrase “go to war” becomes hard to distinguish from going to work. That’s a conflation fraught with ethical danger. The barriers to war get lowered.

P.W. Singer, the author of an important new book called “Wired for War,” told me that, “We are at a breakpoint in history. The U.S. Air Force this year will train more unmanned system pilots than fighter and bomber pilots combined. And, as Bill Gates has noted, robotics are now where computers were back in 1980.”

Now you might think that a “pilot” sitting behind a computer bank in Nevada blowing away people in Afghanistan is less liable to combat stress than a soldier in a unit deployed there, but Singer said the opposite has often proved the case

It’s time for a reckoning, especially from a president who campaigned so vigorously against the “dark side” of the war on terror. Congressional review of the drone programs and the full implications of robotic warfare is essential to cast light and lay ground rules. The Obama administration should not be targeting people for killing without some public debate about how such targets are selected, what the grounds are in the laws of war, and what agencies are involved. Right now there’s an accountability void.

There are also broader questions. When robots are tomorrow’s veterans, does war become more likely and more endless? Do drones cow enemies with America’s technological prowess or embolden them to think America is not man enough to fight? What is the psychological toll on video-screen warriors?

There’s nothing innocent after all about the fluttering of a fruit fly’s wing.