Ground-nesting Bees 2015

Ground-nesting Bees

There are 20,000 species or so of bees worldwide with 4,000 or so in North America. Of those, 70% are ground dwellers (and well-over 90% are solitary, although much of what we know about bees is about the introduced, social European honeybees which are but one of the thousands of bees and very much the exception). Many of these ground dwellers like the ones in photo are in deep trouble due to man’s activities: alteration of habitat, introduced species of both plants and organisms which compete, parasitize, or don’t provide for their requirements, our agricultural practices like tilling or plowing which destroys most nests, mulching, use of pesticides or herbicides and such. Bare patches of soil or overturned tree roots from down trees are extremely important in providing nesting sites for many species, although we find them an eyesore and try to get rid of them.

Also, I should point out that many species CAN sting (and, again unlike honeybees, can sting multiple times) but just don’t. Stingers on these types of critters are modified ovipositors (egglayers), so only females can sting (males in most bee species by the way are excellent pollinators since they are solitary and have to fend for themselves, again unlike the European honeybee). Solitary bees are very unlikely to sting because they are not social. If they die defending their nest (since the bee is the mom, queen, and worker altogether), then their nest and young will die as well anyways, so they would rather just abandon their nest or avoid confrontation altogether.

Social bees like honeybees (and a few bumblebees and wasps like yellowjackets or hornets) have a different mindset. They are all sisters who do not reproduce individually, but rather have their queens do so. Their own lives matter little since there will be others to take care of the nest. All their reproductive success is tied into making sure the nest survives so they are more than willing to die defending it (or defending their sisters). So the solitary bees just avoid a fight and are very unlikely to sting unless under dire circumstances.

Solitary bees are great pollinators of plants and in many cases are better than introduced species (after all, they evolved together with the native plants and are closely tied to them and have been pollinating them well before any introduced species were doing so).

By the way, we also get calls later in the year about ground nesting solitary wasps which people confuse for bees. Many of these in our area are Sand Digger Wasps. The most common ones around here are stinkbug specialists. They sting and paralyze stinkbugs which they drag down their burrow and which then provides nourishment for the developing wasp larvae. I suspect that with the increase in the introduced Brown Marmorated Stinkbug, these wasps have also increased in number. I also suspect that they will help keep the numbers more in control once their own populations catch up with them. We’ll see. I just wanted to point out a few things about bees since I think they’re such an important part of our natural world and so little is known about the majority of them.
- by Alonso Abugattas, Arlington County Natural Resources Manager

Solitary Bee burrows amidst Poverty Oatgrass (Danthonia spicata) and mosses in sandy-loamy bank under oaks of a woodland remnant in the City of Alexandria, Virginia. This is the natural, biologically-active setting under oaks throughout our region and maintaining areas as such - as opposed to emerald-green “dead zones” of fertilized and pesticide-treated turf – is the way to maintain the health and longevity of upland oaks and other trees. Mower-shredded oak leaves left in place are the only “fertilizers” needed in such a "Freedom Lawn". - Numerous diminutive native wildflowers like Common Bluets (Houstonia caerulea) rely on these semi-open areas for their survival. Photo by R.H. Simmons.

Solitary bees often nest in proximity to one another by the dozens and hundreds.