Wasps

What it is

"Wasp" covers a large group of insects, most of which are harmless or beneficial. The ones that cause concern around homes are the social wasps, which live in colonies and defend their nests: paper wasps, yellowjackets and hornets. Penn State Extension's guide to common social bees and wasps of Pennsylvania describes how these insects differ in nesting behavior, life cycle and how they come into conflict with people.

Social wasps are also useful. They prey on flies, caterpillars and other insects, and they pollinate flowers while feeding on nectar. Most people only need to deal with a nest when it is located in a place where someone is likely to be stung.

The main groups

• Paper wasps (Polistes): slender wasps with long legs hanging below the body in flight. They build an open, umbrella-shaped comb of papery cells, usually attached by a single stalk under eaves, porch ceilings, railings and in sheds. Colonies are relatively small.
• Yellowjackets (Vespula, Dolichovespula): stockier wasps with bold yellow-and-black markings. Many species build their nests underground or in wall voids, and some build enclosed paper nests in shrubs and trees. Colonies can grow to thousands of workers by late summer.
• Bald-faced hornets (Dolichovespula maculata): black and white wasps, technically a yellowjacket species, that build large, gray, football-shaped paper nests hanging from trees, shrubs and building eaves.
• European hornets (Vespa crabro): larger, brown-and-yellow, that nest in hollow trees and wall voids. They are active at night and come to lights.
• Mud daubers and other solitary wasps: do not form colonies, rarely sting, and are generally harmless.

The annual colony cycle

Social wasp colonies in the Mid-Atlantic are annual. In spring, a fertilized queen that survived the winter starts a nest alone and raises the first workers. In summer, the colony grows. By late summer and fall, the colony produces new queens and males. After the first hard frosts, the old colony dies. Only the new, mated queens overwinter, hidden in protected places. The old nest is not reused.

This explains why wasp trouble is worst in late summer and early fall: colonies are at their largest, natural food supplies are shrinking, and yellowjacket workers become aggressive scavengers around people's food and drinks.

How to recognize it

Quick field guide

• Paper wasp: slim waist, long dangling legs in flight, brown or reddish with yellow markings. Open comb nest, no outer envelope, often visible from below.
• Yellowjacket: compact body, bold yellow and black bands, a short and rapid, side-to-side flight near the ground. Nest entrance is a small hole in the ground, wall or other cavity, often with traffic streaming in and out.
• Bald-faced hornet: black body with white face and markings. Large gray papery nest hanging above the ground.
• European hornet: large, reddish-brown head and thorax with a yellow abdomen.

Look-alikes

• Honey bees are fuzzy, golden-brown, and live in wax combs. They are important pollinators and should not be treated as wasps. If you suspect honey bees, call a beekeeper or a professional who can help.
• Bumble bees are large, round and fuzzy, and nest in the ground or in grass. They are gentle unless the nest is disturbed.
• Carpenter bees drill round holes in wood, and the males hover aggressively but cannot sting.
• Flower flies (hover flies) mimic wasps but are harmless flies with two wings and short antennae.

Signs of a nest

• Steady flight traffic to and from the same spot.
• A visible nest under eaves, in trees or shrubs, or a hole in the ground with wasps coming and going.
• Chewed wood fibers or papery material.
• A buzzing sound inside a wall.

Where you will find it

Where wasps nest

• Under eaves, soffits and porch ceilings, in attic vents and behind shutters. Common for paper wasps and sometimes hornets.
• In shrubs, trees and hedges. Common for bald-faced hornets and some yellowjackets.
• Underground, in old rodent burrows, along lawn edges and in landscaping. Typical for many yellowjackets.
• Wall voids, soffits and attics. Yellowjackets and European hornets sometimes enter through small gaps.
• Sheds, grills, play equipment, mailboxes and outdoor furniture.

Where wasps forage

In late summer, yellowjackets are drawn to sweet drinks, soda cans, fruit, meat and trash. Picnics, patios, garbage cans and outdoor dining are the places people are most likely to be stung.

Seasonality

Nests are small in spring and early summer, and grow large by August and September. Wasp activity ends with the first hard frost.

Why it matters

Stings

Wasps sting to defend the nest. Unlike honey bees, wasps can sting multiple times. A sting causes immediate pain, redness and swelling. Most people recover in a day or two.

Allergic reactions

Some people are allergic to wasp venom. A serious reaction (anaphylaxis) is a medical emergency. Symptoms include hives, swelling of the face or throat, difficulty breathing, dizziness and a rapid pulse. People with a known allergy should talk with their doctor about an action plan.

Multiple stings

Disturbing a nest, such as by mowing over an underground yellowjacket nest, can lead to many stings. Large numbers of stings can be dangerous even for non-allergic people, especially children, older adults and pets.

Risk around buildings

Nests near doors, patios, play areas or in wall voids raise the chance of stings. Wasps in wall voids can chew through drywall and occasionally enter living spaces.

What to do

Reduce the chance of conflict

• Keep food and drinks covered outdoors. Check cans and cups before drinking, since wasps can crawl inside.
• Keep trash in tightly closed containers and clean up spills and fallen fruit.
• Wear shoes outdoors, and avoid strong floral scents when wasps are active.
• Stay calm if a wasp approaches. Slowly move away. Swatting often provokes stings.
• Inspect the property each spring and early summer for small, new nests under eaves, railings and in sheds, from a safe distance. Early nests are easier to deal with, which a professional can do.

Seal gaps (when no nest is active)

Small openings in siding, soffits and vents are possible entry points for yellowjackets and hornets. Note gaps for repair after any nest has been professionally dealt with. Do not seal an opening with a nest behind it.

If you are stung

• Move away from the nest quickly.
• Wash the area with soap and water and apply a cold compress. Elevate the limb if swollen.
• An over-the-counter antihistamine or pain reliever may help with itching and discomfort; follow label directions.
• Watch for signs of a severe reaction. Call 911 for trouble breathing, swelling of the face, lips or throat, dizziness, a fast pulse, widespread hives or vomiting.

What not to do

• Don't try to remove a nest yourself. Knocking down, burning, flooding or spraying a nest triggers defensive attacks, and injuries are common. Ladders and spray cans make it worse.
• Don't block the entrance to a nest in a wall or the ground. Trapped wasps can chew through to the living space.
• Don't swat at flying wasps or disturb nests while mowing or trimming. Check the area before using noisy equipment.
• Don't treat honey bees as wasps. Honey bees are protected pollinators and often can be relocated.

When to call a professional

Wasp nest removal is a good example of a job that looks simple and isn't. Most stings happen when homeowners try to remove a nest themselves.

Call a pest professional if

• You find a nest near an entrance, patio, play area or walkway.
• Wasps are coming from a hole in the ground or a wall.
• The nest is large, hard to reach or high off the ground.
• Someone in your household is allergic to stings.
• You aren't sure whether you have wasps or honey bees.

A professional can identify the insect, assess the nest location, and remove or treat it safely with the right equipment. Timing matters, so ask about the best approach for your situation.

Call a doctor or emergency services if

• Someone has symptoms of a serious allergic reaction. Call 911.
• Someone has many stings, such as from a disturbed nest.
• A sting site shows signs of infection (spreading redness, warmth, pus) or swelling that keeps worsening after a day or two.