|Nest entrance (lower center) at base of tree.|
|Yellowjacket wasps guard entrance to nest.|
Between mid-summer and early fall yellowjacket wasps that nest underground can be a real threat in some areas. These yellowjacket wasps hide their nests underground, often in cavities made by decaying roots, stumps (see photo) or rodent burrows. Nests may contain hundreds to thousands of worker wasps that will aggressively defend the nest against all intruders.
When disturbed wasps can swarm from this ground nest. A single sting can provoke other wasps that are summoned to attack the "enemy" of the nest (for this reason always quickly leave the area if you are stung). Wasps are especially sensitive to ground vibrations or low frequency (bass) noise as this may signal an animal such as a bear or skunk trying to dig out the nest. This is why wasps will sometimes swarm in response to a careless hiker that steps on the nest entrance or the low growl of a passing lawnmower.
|Notice surface of papery nest in center right.|
|Ground-nest structure (drawing).|
Ground nests can be left alone as long as they are not in an area where they pose a threat from an unwary person. They can, however, be especially dangerous when they occur near playgrounds, picnic areas or along hiking trails.
Threatening nests can be destroyed by treating the nest entrance with a "Wasp & Hornet"- type insecticide. For details see "Treating Yellowjacket Nests".