Athough I’m not a hundred percent sure, I believe we are blaming the wrong shrew for damage wrought on bee hives in Canada and northern parts of the United States. Both Fletcher Colpitts, Chief Apiary Inspector of New Brunswick, Canada, and the Bee Informed Partnership website are blaming the European pygmy shrew, Sorex minutus, for the destruction. However, I can’t find evidence that the European pygmy shrew even lives in these areas. It seems more likely that the native species, the American pygmy shrew, Sorex hoyi, is the culprit.
According to the Smithsonian National Museum of Natural History, the American pygmy shrew is found throughout much of Canada and in certain northern parts of the United States. It is an extremely small mammal, averaging about 3 grams when fully grown. According to the University of Michigan, this shrew can grow to about 90 mm in length, although about a third of that is tail.
Shrews love a bee hive
The problem for northern beekeepers is that the pygmy shrew, which survives on a diet of invertebrates, has discovered that honey bee hives have much to offer: a nice warm place to eat with lots of fresh meat on the menu. They can squeeze through a hole less than 1 cm in diameter, so standard mouse guards won’t keep them out.
I didn’t know anything about shrew predation until I began asking other beekeepers what I was seeing last winter. During the coldest months, when no yellowjackets or similar predators are around, I was finding legs, wings, and headless bees with hollow thoraxes on the landing board of one particular hive. Other hives in the area were unaffected. Each day I would brush the entrance area, but by the next day the body parts reappeared.
Phillip Cairns, a beekeeper from Newfoundland and author of Mudsongs.org suggested it might be shrews, and I believe he is correct. Not only is the evidence consistent, but I see dead shrews once in a while—courtesy of my cat—so they definitely live in my area.
Shrews apparently have a very high metabolism and have to eat constantly in order to keep going through the winter. From accounts I’ve read, the shrews hunt at the outer surface of the honey bee cluster, snatching those bees that are cold and slow. Once captured, the shrews like to consume the contents of the thorax. They get into the thorax by pulling off the bee’s head or drilling a hole right through the exoskeleton, leaving it hollow, and scattering wings and legs in the process. They also leave a trail of fecal matter wherever they go.
Those who have dealt with shrews in the past find that a quarter-inch mesh (6 mm) will keep them out. The problem with quarter-inch mesh is that it will knock the pollen loads from the honey bee’s legs, so it can only be used when pollen collection is not occurring. At other times, a larger mesh must be used, at least 3/8 (10 mm).
In the past, Phillip has lost a number of hives to shrew predation. My colony survived the winter, although it was small and slow to get restarted in the spring. When I opened the hive on a warm day, I did not find a shrew, but I did find many more of the hollowed out bodies and piles of poop, especially on the top bars. It is still not clear to me whether the shrews spend the winter in there the way mice do or if they come and go, but they definitely disappear in spring when the bees get feisty enough to chase them away.
I will definitely be screening that one hive and maybe the ones near it. And if anyone can shed light on the species issue (Sorex minutus vs. Sorex hoyi) I’m eager to know the answer.
The following photos showing shrew damage in a winter hive are courtesy of Phillip Cairns of MudSongs.org.