While many people commonly associate hornets with large, exposed nests, certain species build their homes hidden beneath the ground. This subterranean nesting often leads to confusion, as these insects share characteristics with other stinging species. This article will explore the primary species that nest in the earth, the unique attributes of their hidden constructions, and their overall behavior and role within the natural world.
Primary Ground-Nesting Hornet Species
The European hornet (Vespa crabro) is the only true hornet species in North America, introduced from Europe in the mid-1800s. These large insects have a reddish-brown head and thorax, a yellow and black-banded abdomen, and reddish-orange wings. Their eyes are distinctly C-shaped. Workers are typically 25 mm (1 inch) long, and queens can reach 35 mm (1.4 inches).
European hornets are often mistaken for Yellowjackets, social wasps from the genera Vespula and Dolichovespula. Yellowjackets are generally smaller, with workers around 12 mm (0.47 inches) and queens up to 19 mm (0.75 inches). Their bodies are marked with alternating black and bright yellow bands and are mostly hairless and shiny, unlike the slightly hairy European hornet. Many Vespula species, including the Eastern yellowjacket (Vespula maculifrons) and the German yellowjacket (Vespula germanica), commonly build underground nests.
Characteristics of Ground Nests
Ground nests are typically built within existing cavities, such as abandoned rodent burrows, hollow logs, tree roots, or voids in walls and attics. The insects chew wood fibers and mix them with saliva to create a paper-like pulp, which they then use to form the nest’s structure. This material has a coarse, thick, tan or gray papery texture.
The entrance to a ground nest varies. Yellowjacket entrances often appear as a small hole, about an inch and a half in diameter, surrounded by a conical pile of excavated dirt. European hornet nests underground, especially in wall voids, may not have an obvious external structure but can be identified by a portion of the papery nest extending outside. Nests in protective cavities often lack the distinct outer paper envelope seen in exposed aerial nests. These subterranean nests can grow considerably, with yellowjacket colonies reaching thousands of workers and European hornet nests up to 800-1000 workers by late summer.
Behavior and Ecological Role
Ground-nesting hornets and yellowjackets exhibit distinct behaviors throughout their seasonal life cycle. Queens overwinter in sheltered spots like hollow logs or leaf litter, emerging in spring to build a small nest and lay eggs. Once the first generation of sterile female workers emerges, they take over nest expansion, foraging for food, and caring for the developing larvae. The colony grows throughout the summer, peaking in late summer or early fall.
Their diet varies seasonally. In spring and early summer, both European hornets and yellowjackets are primarily predatory, hunting insects like flies, grasshoppers, caterpillars, and other wasps to feed their protein-hungry larvae. In late summer and fall, adult insects shift to carbohydrates, seeking sugary sources such as ripe fruits, tree sap, flower nectar, and human foods, a dietary shift that often leads to increased interactions with humans during outdoor activities. European hornets are unique for their nocturnal activity, sometimes attracted to lights at night. While generally not aggressive unless their nest is disturbed, these insects contribute to the ecosystem by preying on other insects.