Ground-Nesting Bees on the Wing

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The starting point for yesterday's Southwest Ohio BYGLive! Diagnostic Walk-About held at Spring Grove Cemetery and Arboretum was inadvertently located in the middle of a very busy ground-nesting bee bailiwick.  This sparked an impromptu discussion on the behavior and importance of these native pollinators.  First on the agenda was the total lack of aggression by these small bees; no one was stung or even threatened.

 

Ground-Nesting Bee Burrows

 

There are a number of species of ground-nesting bees representing several hymenopteran families; many are important plant pollinators.  The species observed yesterday waking from its winter slumber in Spring Grove belongs to the family Andrenidae.  Members of this family are referred to by several common names including Andrenid bees and solitary bees; however, these small (3/16 - 3/4" long) bees are most often called "ground-nesting bees," as well as "burrowing bees," or "digger bees" owing to their soil excavating nesting habit.  . 

 

Ground-Nesting Bee

 

The female bees dig individual burrows several inches deep into the soil.  They prefer to nest where the soil is lightly exposed due to sparse vegetation such as areas with weakened turfgrass.  Each burrow consists of a hole about the diameter of a wooden pencil surrounded by a mound of loose, excavated soil particles.  The size, shape, and color of the soil particles may cause the mounds to be mistaken for those produced by ants.  The loose soil particles may disappear after a heavy rainfall leaving only the hole.  The females become receptive to mating after they provision their burrows with wads of pollen to nourish their larvae.

 

Ground-Nesting Bee

 

Ground-Nesting Bee Burrows

 

These are solitary bees with no social structure; however, large numbers of females often locate their burrows in close proximity to one another giving the appearance of an organized colony.  The males will cruise menacingly just above large collections of burrows; however, the males lack stingers (= ovipositors)!  While the females are busily digging and provisioning their burrows, the males buzz back and forth chasing other males and possibly predators.  This presents the appearance of a "swarm of bees," but it's all a rouse.

 

Ground-Nesting Bee

 

Indeed, fear of these highly beneficial insects may be calmed through education.  With the recent heightened awareness of the importance of our native pollinators and interest in supporting their interests, some home gardeners may be convinced to except the honor bestowed on their property by these small but powerfully important bees.  Not every landscape is suitable.  Females prefer to excavate where the soil is exposed by sparse vegetation such as in thin, weakened turfgrass.  Thickening the turfgrass through applying good management practices will create an environment less favorable for these bees and they will simply move to another location.  Some dedicated gardeners may view this as a loss.