Managing Yellowjackets
Identification
Yellowjackets are commonly confused with honey bees. Yellowjackets are
the same size as honey bees, but have bright yellow and black stripes
and very little hair. Honey bees tend to be covered with pale yellow fuzzy
hairs without a distinctive stripe pattern. Popular cartoon depictions
of honey bees are often misleading...and look more like yellow- jackets
than the honey bees they portray.
The two common species of yellowjackets in the midwest are the eastern
yellowjacket which usually nests in the ground and the German yellowjacket
that has a habit of nesting in wall voids of structures. Yellowjacket
workers, the most commonly encountered yellowjackets, are about 1/2
inch long. The queen is about 3/4 inch long.
Biology
Yellowjackets, like other social insects, have a caste (division of labor)
system. Each nest has a queen whose purpose is to reproduce. Male yellowjackets
fertilize the queen and sterile female workers find food, take care of
the queen, defend the nest and care for the young.
Single queens begin building nests in the spring (May). Depending
on the species, she will locate a hole underground, often an abandoned
rodent burrow or in a structure and construct a golf ball sized nest
of paper that is made by mixing wood fibers with her saliva. She lays
eggs and cares for the grub-like larvae in the nest. The first generation
of sterile female workers emerge in June and assume the care of the
nest which allows the queen to concentrate on reproduction. Yellowjacket
adults feed on nectar, fruit juices, sap and other liquids and provide
insects and carrion to the larvae. The population of worker yellowjackets
increases during the summer and peaks in early to mid-August. Nests
may contain 1,000 to 5,000 workers and may measure three to four feet
in diameter.
From late summer into early fall the queen produces queen and male
yellowjackets. Each nest can produce thousands of new queens. Queens
and males swarm from the nest and mate. The males, workers and old queens
die as winter approaches. Newly mated queens seek overwintering sites
in protected places such as logs, under bark or leaf litter and occasionally
in structures. They remain dormant through the winter and begin the
cycle once again in the spring.
Concerns
Yellowjackets are beneficial insects in the sense that they pollinate
plants and feed other insects and carrion (dead meat) to their larvae.
Many times they will prey on insects that we identify as pests. Unfortunately,
their ability to sting makes them a considerable health concern. Yellowjackets
alone are responsible for about one-half of all human insects stings.
The stings of social wasps, such as yellowjackets, have evolved as a defense
mechanism. The only purpose for the sting is to inflict pain. Yellowjackets
are easily provoked and, unlike honeybees, can sting more than once. They
will attack in force if their nest is disturbed. Unless a person is allergic
to yellowjacket venom, stings are rarely life threatening.
Avoidance
Yellowjackets are most frequently encountered when they scavenge for food.
Their habit of feeding on nectar and sugar can create a nuisance. Yellowjackets
locate places where sweet food products have been served throughout the
summer such as picnic facilities, ice cream stands or soda fountains.
In the fall, these locations usually have extremely high yellowjacket
populations. By avoiding these areas or eating in screened areas, contact
with yellowjackets can be reduced.
Yellowjackets are attracted to open cups and cans of soda and other
sweet liquids. They are also attracted to open cans of garbage, bright
flowery clothing and floral scented perfumes. All outside garbage cans
must be kept clean and well covered, to reduce yellowjacket problems.
Contact with the wasps can be decreased by reducing these attractions
at picnics and other outings. In situations closer to home, the elimination
of overripe fruit from gardens and orchards will dramatically decrease
the number of scavenging yellowjackets. Holding gatherings indoors and
using screens on windows will also help avoid yellowjacket problems.
There are a variety of traps on the market that claim to attract yellowjackets.
These traps are baited with the scent of rotting fruit or other odors
equally as appetizing to the yellowjackets. It is questionable whether
these traps can out compete the natural and man-made attractants described
above. However, it is certain that through proper sanitation and removal
of natural and man-made attractants, yellowjacket contact can be educed.
However, in situations where the potential for repeated human contact
exists, other management methods may be necessary.
Management
Management of each species of yellowjacket differs because of their nesting
habits. Both species do not reuse their nests, therefore what was a problem
this year may not occur next year. Caulking cracks and crevices in structures
in winter and early spring, after the nests have died, will prevent German
yellowjackets from constructing nests inside buildings. Openings to active
nests should not be caulked.
Chemical control for ground-nesting yellowjackets consists of drenching
the exit hole with an approved insecticide and plugging the hole with
treated soil or cotton balls. Yellowjackets that are not killed by the
initial treatment will be killed by chewing on the treated cotton ball
or tunneling through the soil. Yellowjacket entrance holes in buildings
can be treated with approved insecticide dusts. As the yellowjackets
walk through the dust they pick it up on their legs and transport it
into the nest. When yellowjackets groom themselves they ingest the dust
on their legs. It may take up to a week for the colony to die and repeated
chemical applications may be necessary. When the entrance hole of an
active nest is in a building, the hole should not be plugged with the
insecticide or caulked. The yellowjackets may decide to chew through
the soft inside wall rather than chew through the insecticide or caulking
material.
Implement chemical control measures at dusk or dawn when the wasps
are in their nest. Wear protective clothing when attempting to eliminate
the nests, such as long sleeved jackets, gloves and pants. Tape the
wrists and ankles to the clothing, to prevent the wasps from getting
underneath the clothes. A bee veil or other enclosed form of face and
neck protection should also be worn. Yellowjackets will defend their
nest, so to avoid being attacked, use a flashlight covered with red
cellophane when applying the insecticide at night. Yellowjackets are
unable to see red. In sensitive locations, or where control has not
been effective, professional pest control operators should be consulted
to handle the problem.
Source: University of Illinois and Illinois Natural History Survey.
Annual White Grubs Update
Adult annual white grubs are still flying in Illinois, which means that
egg laying is still occurring. As we move into August, keep a lookout
for damaged turf in irrigated areas where preventive treatment with imidacloprid
(Merit, Grubex) have not been applied.
As damage starts to occur, lawns in which more than 10 or 12 annual
white grub larvae are present per square foot may require rescue treatments
with Proxol or diazinon to reduce turf damage. Drench treated areas
with at least 1/2 an inch of water within 30 minutes of the insecticide
application to move the insecticide into the root zone where the larvae
are feeding. To avoid turf damage by native wildlife that feed on grubs
(raccoons and skunks, for example), treatments may be necessary at grub
populations lower than 10 or 12 per square foot.
Late Summer 1997
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