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As of the summer of 2002, entomologists at University of California-Riverside
are embarking on a 3-year study to document the distribution
of the German yellowjacket in southern California and develop
a control program involving environmentally safe baits. The first
part of the study entails determining exactly where the German
yellowjacket and our native species live. The wasp to the right
is a German yellowjacket queen.
History
In southern California, the most widespread yellowjacket has
historically been the native, western yellowjacket, Vespula
pensylvanica. The German yellowjacket, V. germanica,
became established in the Northeastern U.S. in the 1970s and
then the Pacific Northwest in the 1980s where it spread down
the coast. It reached southern California in 1991 becoming part
of our fauna. There are other Vespula species as well
but they are not nearly as common in urban southern California,
and they are not considered to be pests.
Species differences
Yellowjackets are adapted for temperate climates so therefore,
you find more species in the northern than southern United States
and more in northern California in comparison to southern California.
There are differences among the yellowjacket groups that translate
directly into whether a particular species is an urban pest yellowjacket.
First, the non-pest yellowjackets. In the western U.S., yellowjackets
belong to either the genus Dolichovespula or Vespula.
Within the Vespula species, there are several groups,
most notably, the Vespula rufa group and the Vespula
vulgaris group. The Dolichovespula wasps and those
of the Vespula rufa group are strictly insectivorous.
What this means to humans is that they are beneficial wasps because
they eat many disease-spreading or crop-eating insects like flies,
caterpillars, grasshoppers, etc. that are detrimental to humans.
These insectivorous wasps ARE NOT scavengers for meat and, therefore,
they are not pests at our picnics, outdoor receptions, campgrounds,
etc. There are several species of these wasps in southern California
(Dolichovespula arenaria in the mountains, V. sulphurea,
the California yellowjacket in the mountains and foothills, V.
atropilosa, a montane species, and north of Santa Barbara,
one might find V. consobrina). These wasps typically make
small colonies with only a few hundred wasps at peak population
and the nests typically die out by the end of summer. These wasps
may occasionally seek out sweets from our sodas and fruits, however,
most of the time, they leave humans and their food alone and
they rarely show up in yellowjacket traps.
In contrast, the pestiferous wasps are members of the Vespula
vulgaris group, which have nests with peak wasp population
numbering in the several thousands and they continue their life
cycle well into the late autumn. Although they do collect insect
prey, they also scavenge meat which puts them into contact and
conflict with humans. These are the wasps which harass us at
outdoor eateries, theme parks, receptions and picnics, congregate
at bakeries or candy factories, seek out spilled sodas at sporting
stadiums, etc. Basically, their scavenger behavior puts them
into interaction with humans which increases the potential for
sting incidents as well as being a nuisance which could curtail
or cancel outdoor activities. In southern California, there are
two species representing the V. vulgaris group, the western
yellowjacket, V. pensylvanica and the German yellowjacket,
V. germanica.
There are subtle behavioral differences between the western and
German yellowjackets. The western yellowjacket appears to nest
predominantly in hilly areas and makes its nest in the ground
in abandoned rodent burrows. Therefore, one typically finds the
western yellowjacket around natural areas, in foothills and such
and rarely finds them in the middle of urbanized regions. In
contrast, the German yellowjacket typically makes nests off the
ground and hence, uses wall voids and cavities in places like
palm trees that are covered by fronds. Because of their association
with homes, German yellowjackets are found in urban areas where
previously, yellowjackets had been absent for years. Because
areas of southern California differ so markedly, we are attempting
to determine how the population composition of the two yellowjacket
species changes as one moves through Los Angeles.
It is important to know where each species is dominant because
there are species differences in food preferences which could
be important in the development of control measures. These food
preferences would be fine-tuned in order to maximize control
efficiency, using the best bait for the specific species.
How to identify yellowjackets
Yellowjackets are amazingly easy to identify to species. Most
of the time in entomology, if you try to identify an insect to
species you must dissect out some very obscure body part and
compare it to some arcane illustration. With southern Californian
yellowjackets, you use coloration and markings that you can see
most often without a magnifying lens. First of all, you need
to know that you have yellowjackets because despite what may
seem very simple, many people still mistake other flying insects
as yellowjackets
Not a yellowjacket
 Honey bees (right) are mustard yellow and brown
and are covered with many hairs to which pollen adheres. They
have stocky bodies. Honey bees harvest nectar (carbohydrates)
and pollen (protein) from flowers and NEVER are attracted to
meats.
Paper wasps (left) are often mistakenly called yellowjackets
by the non-entomologist. These wasps are much longer in body
and have a very thin "wasp-like" waist. They make nests
under the eaves of houses, in bushes, in empty boxes and garden
pots, etc. These nests are relatively small, consist of only
one layer of comb for brood rearing and are never covered with
a paper envelope (that is, when you look at the nest, you can
see the wasps and the comb; yellowjacket nests are covered with
a paper envelope). Paper wasp nests only reach a colony size
of about 100 wasps. Paper wasps are brown and yellow whereas
yellowjackets are usually black and yellow.
There are many other insects that mimic yellowjackets. These
include flies (e.g. the stratomyid below), moths, and other wasps
(eg the scoliid, right) This mimicry gains them protection from
predators who avoid them thinking that if they attacked one,
they would get a nasty sting. 
Identification of southern California yellowjackets in the Los
Angeles Basin
Southern California yellowjackets are black and yellow (one
species, V. consobrina is black and white but is found
north of the LA basin) and typically are rather smooth (not hairy)
in appearance. Some people think that they are bees because they
have stocky bodies like honey bees. The fact that one of their
common names is "meat bees" doesn't help to defray
the confusion. Almost every yellowjacket that you will collect
will either be a western or German yellowjacket but included
here is one other just in case you run into it.
1 - Does the wasp have two longitudinal bands on its thorax
(2nd body part) like the wasp on the far right?
- if yes, it is the California yellowjacket, V. sulphurea
- if no, continue to the next step
 
2 - When looking straight down on the wasp's head, are there
yellow rings completely encircling the eyes?
- if yes, it is the western yellowjacket, V. pensylvanica.
(There will also be a yellow blotch of pigment on the first antennal
segment.)
- if no, continue to the next step
3 - When looking straight down on the wasp's head, is the
yellow ring broken up around the eyes?
- if yes, it is the German yellowjacket, V. germanica.
(Also, the first antennal segment will be completely black).
- if no, either you don't have a yellowjacket, you have a male
yellowjacket, or you have a species not considered here.
A subtle point: the coloration of the abdomen is often a soft
lemony yellow in the native western yellowjacket while it is
brighter "school bus" yellow in V. germanica.
Contact information
see wasps home page
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Identification
Guide for Southern California Yellowjackets 
