Egg -- Wasp eggs are small, white and sausage-shaped.
Larva -- Wasp larvae are legless white or cream grubs with pale to dark brown heads. Larvae of most species are at least 14 mm long when fully grown.
Pupa -- Pupae are slightly shorter than mature larvae and develop within silken cocoons in cells within the nest.
Hosts -- These wasps prey on many types of insects, particularly caterpillars, although hornets and yellowjackets are also attracted to meat and sweet drinks.
Damage -- Because they prey on many harmful insects, these wasps actually perform a beneficial function. However, when they nest in lawns, yard trees and eaves of houses, wasps may interfere with outdoor activities. Wasps are likely to sting anyone who disturbs their nest. Paper wasps, however, tend to be less aggressive than hornets and yellowjackets. Wasp stings are painful and cause severe allergic reactions in some people.
Life History -- The nests of hornets, yellowjackets and paper wasps are abandoned each year. In fall, virgin queens and males leave the nests and mate. The males and workers eventually die, but the queens overwinter in rock cracks, under bark, in houses or underground. In spring, queens emerge and begin building nests. Hornet nests are usually constructed above ground in trees or shrubs; whereas those of yellowjackets are usually constructed underground. The European hornet usually constructs nests in hollow trees. Paper wasps make papery, honeycomb-like nests usually located above ground in trees and dense shrubbery, under eaves, or some sheltered area.
After constructing a small nest, the queen lays a single egg in each cell of the comb. Two to 3 days later, the eggs hatch and the queen begins to feed masticated insects to the larvae. Within 12 to 18 days, the larvae mature. Fully grown larvae spin silken caps over their cells and pupate. About 12 days later, new adult workers emerge. These workers attend and feed larvae that develop subsequently, enlarge nests, and under some circumstances (e.g., death of queen), lay male eggs. After raising the first brood of workers, the queen remains in the nest and deposits eggs. Hornet and yellowjacket queens produce about 1500 eggs; paper wasp queens may lay several hundred during their lifetime.
Insecticides may be dusted or sprayed into the entrances of hornet or yellowjacket nests whether above ground or below ground. Openings of underground nests may be closed with a shovel full of moist soil after treatment. Paper wasp nests are easily treated since they are open and exposed.
Occasionally yellowjackets and hornets build nests inside the walls of buildings. In such cases, the knothole or crack entrance should be located and treated, but not plugged so that returning wasps can carry the pesticide into the nest and contaminate the whole colony. Most pesticides are effective within 24 hours.