There is just something about the sound of a bumblebee that really gets a dog's attention. Most dog owners have witnessed their pets go on high alert at the sound of a bee or a large fly.
The behavior of a dog when it detects the sound of a bumblebee is unmistakable. Head up, eyes wide open and head quickly moving from side to side in an apparent effort to locate the source of the sound.
Of course, the fact that dogs have an acute sense of hearing is well known. Dogs generally notice unusual sounds in the environment – sounds that humans frequently don't detect. For example, the distant sound of thunder.
But evidence suggests a bumblebee is more than environmental noise, it is a canine call to action. That action is to locate the insect and dispense with it as quickly as possible!
A dog's approach to killing a bumblebee resembles any other canine display of aggression. The dog bares its fangs and starts snapping at the insect. It will keep snapping until the insect leaves or is knocked to the ground. At this point, the dog will bite the insect several more times in an apparent effort to make sure the offending hexapod is dead. The dog always keeps its lips out of harm's way.
This brings up an interesting question. It appears that a dog knows that the insect can sting them, thus the necessity of presenting a minimum of its soft tissue as a target by curling up its lips. Is this a case of the dog learning that bees can sting, or do dogs instinctively know that bees can sting?
This was a question that the Russian physiologist Ivan Pavlov addressed back in the late 1800s. In his experiments, Pavlov was able to get a dog to salivate by ringing a bell. The dog used the bell as a cue that it was going to be fed, thus prompting the flow of saliva. Pavlov called this a conditioned response. He compared that to an unconditioned response: He asked, "Are there some things dogs don't need to learn?"
I don't know if the response of dogs to the sound of bumblebees is learned or instinct. I do know that the response is predictable. And just as the sound of the bell triggered a salivation response in Pavlov's dogs, the wing sound of a bumblebee triggers an alert response.
Just last week my trusty beagle exhibited this alert response in the presence of bumblebees flying in my barn. The dog just happened to be near the flight path of the bees to their nest and immediately went into high alert. The jumping and snapping display that ensued was fun to watch. Before I took him away, my beagle had killed seven bumblebees and, to my knowledge, had not been stung.
It appears to me that the wingbeat frequency of the insect is how the dog recognizes a bee. In general, bumblebees have a wingbeat frequency ranging from 130 to 240 beats per second. This produces the familiar hum of a bee. Horse flies also have a wingbeat frequency in this range, and dogs react to that sound in a similar way. Horse flies have a painful bite, so either a bumblebee or a horse fly is capable of inflicting pain. Dogs might have learned that encounters with insects associated with a sound of that frequency was something to be avoided in the same way that Pavlov's dogs learned to associate food with the sound of a bell.
Farm boys and farm dogs, at least historically, learned to deal with bumblebees on a regular basis during the summer months. Bumblebee nests were common in barns, especially in stacks of hay bales. So when the nests were disturbed, the bees were not happy campers and looked to sting in defense of their nest.
Growing up, I remember an incident where a neighbor's collie took the act of killing bumblebees to a new level. Bees were emerging from a hole in a hay bale. The ol' collie put his front paw over the hole and released the bees one at a time, each of which he proceeded to kill with the curled-lip, snapping behavior. Best bumblebee dog I ever saw!