Meet Midge, short for Midget, a Chihuahua Terrier mix and the smallest drug-sniffing dog in the US:
There seems to be a trend towards smaller dogs for police use. Trainer Dave Blosser compares dogs like Midge favourably to larger breeds. "Size-wise, endurance-wise, they last longer," he says. And there are other advantages to smaller dogs, says Bob Eden, who trains police dogs and handlers.
On the other hand, dogs that are too small may not be able to get around obstacles, and there could be a credibility problem, Mr Eden says.
"A Jack Russell terrier may make an extremely capable narcotics dog," he says, "yet some agencies would shy away from such a breed simply because the dog doesn't have the same respect from the public as a Lab or shepherd might."