The photo is immediately unsettling. It purports to show bedbugs creeping out of a seam on a bus seat in Philadelphia.

It surfaced on social media about 6:30 p.m. Wednesday, according to SEPTA. It quickly went viral. Comments on Facebook included "now I'm scared to catch the bus" and "even more reason to validate my choice to never use public buses."

The photo, taken Friday, prompted SEPTA to pull three buses from service on Route 6, which runs from the Olney Transportation Center to Ogontz and Cheltenham Avenues, said spokeswoman Jerri Williams. The buses received a cleaning that included vacuuming and freezing.

"I hope this incident proves we don't want them on our bus," Williams said. "If you tell us, we will pull that bus and we will have that treated immediately."

The picture drew attention to a problem no city department wants to own. Both the Licenses and Inspection and Health Departments say they are not responsible for bedbugs. But last year the city created a Bed Bug Task Force.

"No one is in charge of bedbugs, no one," said Michelle Niedermeier, a member of Pennsylvania State University's Integrated Pest Management and chair of the task force.

No one knows how serious a problem the city may have, she said. A study found about 11 percent of homes had bedbugs, but it only surveyed part of South Philadelphia.

SEPTA didn't identify the insects in the photo, Williams said, but assumed they were bedbugs.

They could have been other things, such as carpet beetles or cockroach nymphs, Niedermeier said.

Riders' perceptions that fabric seats are unclean is prompting the agency to phase out fabric in favor of molded plastic, Williams said. The 550 new SEPTA buses on order will have plastic seats, she said, and since 2013 plastic seats have been installed in subway cars as they are pulled for service.