Bees and Wasps: Danger Can Be Lurking Underground

A woman mowing her grass was killed when she mowed over an underground wasp nest. A gardener lost consciousness from multiple stings when weed pulling disturbed an underground bee nest. Another person suffered permanent scars from vicious hornet stings while cleaning up discarded lumber that hid a nest. Because they are most often seen flying through the air, most people don’t look down when they hear buzzing insects; but a large number of bee and wasp species build their nests underground or under debris lying on the ground.

Like the three real-life examples above taken from GardenWeb.com, Internet gardening forums are peppered with reports of bees, wasps and hornets attacking viciously from underground nests. Quite a few bee and wasp species build their nests underground and several species, taking advantage of the shelter provided by ground surface debris, build their nests under stray boards, loose slabs of rock or in wood piles. Underground bees have even been known to build nests in undisturbed compost piles. 

There are several solitary species of bees and wasps, those that live singly, that nest underfoot. Mud daubers and potter wasps build their single-celled, ground-level nests in wet areas near ponds, poorly drained yards or near dripping outdoor faucets. Digger bees, digger wasps and cicada killer wasps dig single burrows several inches deep into dry or sandy ground. Mammoth 2-inch long cicada killers have a particular affinity for nesting in sand traps which can make them a problem on golf courses. Several solitary bee species, including cicada killers and halictid (sweat) bees nest in groups, locating their individual burrows close together. However, solitary bee and wasp species are relatively docile and not particularly defensive of their nests. They pose only a limited problem to humans, rarely stinging unless stepped on; but their habit of nesting near areas occupied by humans can create occasional problems for gardeners, landscape workers, golfers or barefoot children.

The real threat from underground bees, wasps and hornets (a type of wasp) comes from species that live socially in colonies that can number in the hundreds. Opportunistic insects, social bees and wasps often colonize abandoned animal burrows but will also tunnel into the ground, excavating multiple passages to house the colony and hold the queen’s eggs and developing larvae. Some ground bees such as bumble bees are fairly docile, attacking only when disturbed or threatened. Other ground-dwellers, particularly yellowjackets (a species of wasp) are highly aggressive and may attack without warning. Yellowjackets are so sensitive to noise and vibration that a running lawn mower can trigger an attack.

The sight of attacking ground bees or wasps is frightening. They shoot out of the narrow entrance to their underground nest like a stream of machine gun bullets, attacking and stinging immediately. Releasing pheromones that incite their nest mates to frenzied attack, they will try to swarm over their foe and can be relentless in their pursuit. While many humans can outrun bees and wasps, which have a 6- to 7-mile-per-hour flight speed; the speed of ground bee attacks takes most victims by surprise, causing panic that can hinder their escape to safety. Few people survive a ground bee or wasp attack without suffering multiple stings, particularly in late summer when colonies have reached maturity and stinging insects are at their most aggressive.

Ground bees and wasps pose a considerable threat to humans because they frequently build their nests in areas shared by humans – lawns, gardens, parks and golf courses –and because their nests usually go undetected until they are disturbed and the insects have launched their attack. The slight domes or narrow openings that mark the entrances to underground bee and wasp nests are often hidden by lawn or garden vegetation. The shallow depressions caused by excavated nests can easily be mistaken for natural low spots in a lawn. Nests built under ground debris remain invisible until the debris is removed. When underground bee and wasp nests are discovered it is usually by observation of heavy bee traffic in a specific area. Bees or wasps consistently seen hovering over a patch of lawn or garden generally indicate the entrance to an underground nest. Careful observation from a safe distance will reveal insects entering and exiting an opening in the ground. Heavy bee traffic to and from a piece of debris or woodpile and the sight of insects milling around the area are a good indication that wasps or hornets have built a nest under the debris and into the ground.

The internet offers a number of “home cures” for the elimination of ground bees and wasps. Most of these do-it-yourself pest control techniques are of questionable effectiveness, can be detrimental to landscape plantings, and carry a high element of risk to the home owner’s health and safety. Seldom does a home owner escape without multiple stings when trying to eliminate an underground bee or wasp nest. Until a nest is eliminated and dug up, there is no way to know how large the colony is or how many exit holes the nest contains. Ground nests always have multiple exits. Bees and wasps can easily attack from a secondary exit while a home owner is attempting to treat the primary nest entrance. The elimination of ground bees and wasps should be handled by licensed pest control experts who have the requisite knowledge, safety gear and pest control products and equipment to safely and effectively eliminate dangerous stinging pests.