The enmity between dogs and mail carriers is so well established that it’s become something of a joke. But cute as those Larry the Mailman chew toys may be, dog attacks are a real problem for America’s letter carriers. A recent report from the USPS found more than 6500 attacks on employees in 2015 alone. 

Dog lovers may find this hard to believe, but man’s best friend is not always so friendly. More than 4.5 million Americans are bitten by dogs each year. More than half of the victims are children, who are also more likely to be seriously hurt by a bite. 

But why do dogs hate postal workers so much? They don’t, say dog experts. It’s just that letter carriers a) enter dogs’ territories, which makes the animals feel threatened and defensive; and b) seem to go away when the dogs start barking or get aggressive. The fact that the postal workers leave after delivering the mail reinforces dogs’ certainty that their barking did a good job. 

And it’s not as though postal workers can just skip houses with dogs; after all, that’s 37 to 47 percent of American households. So the mail carriers persist, which brings them into conflict with some very worked-up canines.

Last year, according to the USPS report, 6549 postal workers were attacked, some quite seriously. The report ranked the 30 worst cities for dog attacks. At the very top was Houston, Texas, which saw 77 incidents—up 22 percent from last year. There’s a very practical reason for that says McKinney Boyd, head of USPS public relations for the Houston area: "We deliver more parcels now than before, and we also deliver mail on Sundays,” he told Vocativ. “So we attribute this increase to the increase of parcel deliveries on Sundays ... Delivering mail an additional 51 days of the year has certainly contributed [to increased attacks].” 

To protect its employees, USPS is implementing a new system that requires customers to indicate whether or not they have a dog when requesting a pickup. But there’s a simpler way to prevent attacks, Boyd notes: “Please restrain your dogs."