Ants in Orchards and Vineyards in the San Joaquin Valley
By Devin Carroll 2014
Contents
Introduction: The role of ants in SJV agriculture. - 1
List of ants found. - 4
Ant anatomy and vocabulary. - 5
SJV agricultural ant descriptions and biology, with photos. - 6
Field guide to the common species. - 21
Microscope key to the species. - 23
Bibliography. - 25
The role of ants in SJV agriculture.
As any observer can attest, ants are among the most common insects in agricultural systems.
They play a major and complex role in agricultural ecology, plant and soil health, and pest
management.
This project reflects my personal experience along with supporting information from the
literature. It applies mainly to the areas, the crops, and the seasons where I work. These include
grapes, tree fruit and nuts in agricultural sections of Madera County, most of Fresno County, and
southern Tulare County around Delano and Earlimart. I am in the field mainly from late
February to the end of September.
Almond pests
Ants in almonds get the most attention because two species can be very destructive of nuts
on the ground between shaking and gathering16. Many ants will pick up broken pieces of almond,
but only fire ants and pavements ants can chew holes in whole nuts. Scouts should take care to
distinguish these two pest species from other common orchard ants such as field ants and
pyramid ants.
Due to the almond market, most agricultural ant baits are aimed at fire and pavement ants.
They are “grease” ants, so typical baits consist of vegetable oils mixed with a carrier such as corn
cob grits. These baits miss some of the other ant species.
Soft tissue damage
Most ants do not directly damage plants, but fire ants can be destructive of soft tissue. They
can girdle young grape vines and citrus trees19.
Many ants will feed on fruit that is cracked or damaged. This may actually help the farmer,
because the ants may scrape out a wound before it can rot.
Tenders of honeydew-producing homopterans
Most ants love sugar and are attracted to honeydew-producing homopterans including
aphids, soft scale, mealybugs, whiteflies, and some leafhoppers. The ants magnify infestations
by chasing away or killing parasites and predators. They also move their “herd” within and
between vines and trees. This makes them important indirect pests of most of our tree and vine
crops.
In my opinion, the most effective guards of homopterans in this area are Argentine ants, fire
ants and field ants, in that order. In some cases, these ants can transform a minor pest into a
major problem. Many other ant species seem to make little difference to biological control.
Argentine ants are rare in SJV agriculture, so controlling fire and field ants would likely reduce
our ant-induced problems to a minimum.
On the good side, by cleaning up the honeydew the ants may reduce the damage from sooty
mold growth.
In our area, harvester ants are the only common species that do not tend homopterans.
Predators
Most ants will prey on almost any available arthropod that is not providing them with
honeydew10. This includes some pests, some natural enemies, spiders, and other ants. The role of
ants in pest management is complex as they may help control pests but may also interfere in
biological control by other agents21.
Most predaceous ants also consume sugar, and their numbers depend on sugar sources,
particularly homopterans21.
In almonds and peaches, field ants are key predators of peach twig borers, but not of oriental
fruit moths, which have a spitting defense7. Their role in controlling other pests such as
leafrollers, leafhoppers, katydids, and so on is not well documented but probably in some cases is
substantial. Growers who successfully control their ants should be on the lookout for unexpected
consequences.
Soil builders
Ants contribute positively to soil ecology. They are first responders to dead animals
including vertebrates as well as arthropods, breaking down the bodies in a step towards
converting it to soil. With their deep nests they mix upper and lower soil strata, provide aeration,
and carry organic matter downwards from the surface10.
Seed eating ants may drop seeds, spreading them to new places10. But they may also be so
thorough as to denude patches of ground of almost all vegetation10. Their tastes might play a role
in determining which weeds are more common.
Ant wars
Most ants fight fiercely with their neighboring colonies for territory and food10. Most often
the violence is within the same species, but sometimes two species will fight6. Watching ant
wars as a child in my urban yard was my first experience with entomology, and I still enjoy
watching their gladiatorial combat. As a rule, advantage lies in numbers; many small ants will
defeat a few large ants. The usual tactic is to grab legs or antennae and tear apart the enemy. A
survivor may carry around the severed head of another ant, still clamped onto a limb.
Ants around their home nests tend to be more aggressive towards other species, and
intruders usually try to flee when confronted.
Many ants use chemical warfare to repel other ant species10. Formicinae spray formic acid
from the acidophore. Dolichoderinae use a variety of terpenoids produced by an anal gland and
expelled through a slit opening at the tip of their abdomen. These chemicals produce the
characteristic pungent odor of these ants when crushed. Most Myrmicinae have stingers with
venom that increases their ability to injure and kill arthropods and cause pain in vertebrates.
Chemicals from the venom may also be used to communicate within nests and repel foreign ants.
Ant wars have interesting variants. Some species will make slaving raids to carry captives
back to their own nests, or invade a nest to enslave the occupants in situ10.
New colony formation
Ants establish new colonies in a variety of ways depending on the species, but they may be
categorized into “independent founding” in which new queens found the colonies without
bringing workers, and ”swarming” or “budding” in which workers from the old colony
accompany the queens10. The word “swarming” is sometimes misused to describe ant
reproductives leaving the nest; the better term is “nuptial flight”.
Worker rotation and sprays
Ants practice an efficient rotation of work within their colonies10. The youngest workers
stay deep inside, nursing juvenile stages and tending to the queens and drones. Older workers
perform the more dangerous jobs outside, fighting other ants and collecting food in locations
where they are exposed to predators. This insures that as older workers are lost they are replaced
by others.
Surface sprays that kill only the outside workers are thus only temporary6. New workers will
soon appear. Colony elimination requires that the workers carry toxins back to the nest in bait or
perhaps on their skin. Ants share their food with each other and with their larva (prophylaxis), so
toxins spread through the colony.
In many species worker ants are not capable of consuming solid food10. They feed solids to
the larvae, which eat and digest it before regurgitating some back to the workers.
Baits
For economic reasons most baits are primarily aimed at either Argentine or fire ants.
Argentines are chiefly urban pests, although they dominate in some coastal winegrowing
regions in California. Their baits use sugar as attractant, usually in liquid or gel form. Typical
toxins are boric acid or fipronil. The same baits are effective on many other sugar-loving
household ant pests, but they are less practical in vineyards because of the difficulty of
maintaining liquid bait stations.
Many fire ant baits use a granular carrier soaked in vegetable oil. These baits also attract
other grease lovers such as pavement ants, but they have little appeal to other species such as
field ants. Sugar granules or protein baits attract both fire and field ants, but they are so far not
commercially available.
List of Ants
North America has 10 subfamilies of ants, but all species I have found in the San Joaquin
Valley belong to only three. They are differentiated at the start of the microscopic key.
Those marked with asterisks are not included in this work because I have not seen them in
agriculture or very rarely. Some are more common in urban settings. Some are included in
Ingrid Carmean’s key to local urban ants3, and some are included in publications of the
University of California by Haney et. al.9, Grape Pest Management 13, or at the UCIPM website14.
Subfamily Dolichoderinae
Dorymyrmex bicolor – pyramid ant
Forelius pruinosus – no common name
Linepithema humile – Argentine ant
Tapinoma sessile - odorous House Ant
* Dorymyrmex insanus – pyramid ant3 (=Conomyrma)
* Liometopum occidentale – velvety tree ant9. (Oak, urban yards)
Subfamily Formicinae
Camponotus essigi– carpenter ant
Formica aerata – California gray field ant
Myrmecocystus mimicus – honeypot ant
Nylanderia vividula – crazy ant
Subfamily Myrmicinae
Messor pergandei – Jet black harvester ant
Monomorium minimum – little black ant
Pogonomyrmex californicus – California harvester ant
Tetramorium bicarinatum - Guinea Groove-Headed Ant (= tramp ant)
Tetramorium caespitum – pavement ant
Solenopsis invicta – red imported fire ant
Solenopsis molesta – thief ant
Solenopsis xyloni – southern fire ant
* Cardiocondyla ectopia3
* Cardiocondyla mauritanica – (I found this only in my urban yard)
* Monomorium pharaonis – Pharoah ant3,9 (lighter colored than M. minimum)
* Pheidole californica13 – (I found 1 specimen of Pheidole on the floor of an apple orchard,
another on a citrus tree.)
Anatomy and Vocabulary
(Right) Abdomen: Segment 1, the
propodeum, is attached to the thorax.
The pedicel may have either 1 or two
bead-like segments, the petiole and
postpetiole. The remaining abdomen is
the gaster. (Tetramorium caespitum)
(Below) Anal area of gaster:
Dolichoderinae with slit
(Dorymyrmex bicolor)
Formicinae with acidophore
(Formica aerata)
Myrmicinae with stinger
(Tetramorium caespitum)
Antennae are elbowed, with a long first
segment, the scape, and the remaining
funiculus, which may end with a 2-3
segment expansion, the club.
The clypeus is the area just above the
mandibles.
In addition to the compound eye, alate ants
and some workers have 3 ocelli (not shown)
at the top of the head.
The vertical grooves are characteristic of
pavement ants, Tetramorium caespitum.
Ant Descriptions and Biology
Pyramid ant
Dorymyrmex bicolor
Dolichoderinae
One of our most common ants,
pyramids can be confused with fire ants.
They are about the same size, and have
similar colors; red head and thorax with
a dark abdomen. But pyramids have
only a one-segmented pedicel, and the
workers are all about the same size.
The final test is smell; pyramid ants
have a pungent odor when crushed.
The typical mound is a well-formed
donut-shape. When the sun is not too
hot, pyramid ants run in and out of their
Doughnut shaped pyramid ant mound with ant
hole to add grains to the mound. Unlike
“graveyard” of fire ants.
fire ants, they do not rush out in mass
when disturbed.
Pyramids are aggressive towards any ants that pass near their
nests. They compete fiercely with other species. They can block
foraging of competing honeypot ants by surrounding their nest
entrance and tossing in pebbles10.
Many pyramid ant nests have an ant “graveyard” to the side.
Usually the dead are mainly fire ants. In one case I saw mainly
pavements ants, and occasionally a few harvester ants and field ants
are present.
Pyramids tend homopterans. I often see them on grapes with vine
or grape mealybug, or European lecanium scale. They do not seem
to protect mealybugs very well; I usually observe good biological
control where they are present. Typically the nests are in the open
outside the vineyard, with the ants following a trail in to a vine up to 7 or more yards away.
These ants may also forage by scattering in all directions late in the afternoon.
Pyramids are predaceous. I have seen them carrying leafhopper
Worker showing the
nymphs off of vines. Literature has them eating other ants and a
24
“pyramid” at the rear of
variety of arthropods .
the thorax.
Pyramid ants will pick up bits of almond and carry them to their
Photo by Alice Abela
nest, but they do not chew holes in intact almonds, so they are not
almond pests. Presumably their competition and aggression reduces
the fire ant numbers in almond orchards. They should not be the targets of control efforts in
almonds.
I have seen nuptial flights from late February to mid-April. They might start earlier when I
am not often in the field. Females are red and males are smaller and black.
Forelius pruinosus
Dolichoderinae
This small ant has no common name. I have seen it
in only a handful of locations. It is distinctive among
our ants because the abdomen is yellowish. It has a
pungent odor when crushed.
The mound is doughnut shaped, similar to pyramid
ant nests, but often in a cluster. There may even be ant
graveyards with mainly fire ants. Forelius often forages
in distinct lines like Argentine ants. The mounds are
usually in the open but often near dry straw where they
like to forage and pick up grass pieces.
Forelius pruinosus worker.
I do not have many feeding observations. They are
reported to tend homopterans, but I have not seen them
in grapes, and I have seen their trails bypass weeds with aphids. They also ignored fruit on the
ground. They are predaceous; BugGuide.net pictures show them eating caterpillars and
grasshoppers. I have seen them carry dead ants, and they are very aggressive towards other ant
species. They can surround nests of competing species and keep the residents inside with
repellent chemicals, and sometimes even fill the entrances with dirt10.
Doughnut shaped Forelius pruinosus mound with grass
seeds and ant “graveyard” of fire ants.
Argentine ant
Linepithema humile
Dolichoderinae
Argentine ants, invaders from South America,
now dominate most California cities, including
ours in SJV, but they are not found in most SJV
vineyards and orchards. This differs from some
Argentine ant worker.
coastal grape districts, where Argentines also
Photo by Joyce Gross
dominate in vineyards13. Where present, they
displace native and other introduced species12.
Unlike with most ants, Argentine mated females do not fly to establish new colonies by
themselves12. Also, neighboring nests do not compete and fight with each other. Instead, all the
nests in a neighborhood and beyond form one inter-connecting supercolony, cooperating and
sharing food, workers, immatures, and multiple queens. Multitudes of ants travel in wellestablished lines between colonies and to food sources. New nests are established by budding,
with many workers digging the new holes and bringing in queens. California has only 4 known
supercolonies: one covering most of the state and into Mexico, and 3 smaller supercolonies in the
southern part of the state12.
The lack of Argentines in most SJV farms probably relates to water. They require a steady
source because they desiccate more quickly than native ants13. Because they do not fly, they
cannot cross large dry expanses, or survive for long when the water is turned off. This also
explains why Argentines are most often found in one corner of an orchard or vineyard, next to a
building or garden or other permanent source of water.
Argentines are highly effective at guarding honeydew-producing homopterans from natural
enemies. For example, they can induce massive outbreaks of brown soft scale in citrus, where
normally this pest is hard to find11. In grapes, good mealybug biocontrol becomes impossible
with these ants5.
We have two other small dark ants that resemble Argentines. Both forage solo rather than in
distinct trails. The crazy ant, Nylanderia vividula, is almost the same color and size. It has dark
hairs that may be visible with a hand lens. The odorous house ant, Tapinoma sessile, is black. It
holds the gaster high, hiding the small petiole, which lacks the prominent dorsal scale seen on
Argentine ants. Unlike many Dolichoderinae including Tapinoma, Argentines have only a mild
pungent odor when crushed.
Most baits for Argentines use sugar as the attractant5. Boric acid is a common toxicant
because it is safe around homes and easy to register in agriculture, but control is short-lived
because the supercolony repopulates quickly. Baiting in April-May is most effective because
most reproductive larvae develop at that time5.
Fipronil baits are now the standard in urban areas because control may last for years. Fipronil
termite treatment may also eliminate Argentine ants. Fipronil is not registered in agriculture for
ant baits or most other uses. It has been blamed for some cases of bee colony collapse, and a
defective seed treatment caused a mass bee die-off in France24.
Sugar is highly attractive, but Argentines also seek protein at times of the year when the brood
is growing. For example, dog food is often infested. Oil-based baits aimed at fire ants do not
attract Argentines.
Odorous House Ant
Tapinoma sessile
Dolichoderinae
This small black ant can be confused with Argentine ants. It
is blacker and the petiole is small and hidden beneath the gaster,
which is held high. It has a pungent odor when crushed. It
forages solo. It differs from crazy ants by its more typical-sized
antennae, with the scape only slightly longer than the head.
Tapinoma often occurs on vines with vine or grape
Odorous house ant.
mealybugs; on the roots, trunk, or leaves, or in rotting bunches.
Photo by Charley Eiseman
The nest may be at the vine base but not obvious until disturbed.
Once I found a colony holding their pupae clumped under loose vine bark. Some were carrying
pupae down to the soil. An herbicide sprayer had passed not long before; perhaps the ants had
moved the pupae up to escape a repellent chemical.
I also found this ant on citrus.
I have seen this ant west of Sanger in Fresno County, and near Earlimart in Tulare County.
Odorous house ants can be a household pests14.
Carpenter Ant
Camponotus essigi
Formicinae
Carpenter ants nest in wood. Some species are all-black, but Camponotus essegi has a reddish
head and thorax.
I have only seen this species once, in an organic
vineyard near Del Rey in Fresno County. The ants
were fighting a vicious intra-species war for
control of the vine. Mayhem was so widespread
that I could not find any whole specimens to
photograph or capture.
Carpenter ants have distinct castes, with majors
much larger than minor workers8.
Carpenter ants forage for dead insects, extract
the fluids, and usually leave the exoskeleton
Carpenter ant with one antenna torn off
behind24. They also tend homopterans such as
17
in battle.
aphids . I found them on the same vine as vine
mealybugs.
California Gray Field Ant
Formica aerata
Formicinae
The California gray field ant (AKA native gray
ant) is the most widespread ant in San Joaquin
Valley vineyards and orchards, present in virtually
every block and dominating most13. It differs from
Field ant worker. Photo by Jim Moore.
our other large ants because the head and thorax are
less reddish and the gaster is only a little
darker, giving it a brown appearance.
Camponotus essegi and Myrmecocystus
mimicus both have a redder head and
thorax. Formica aerata can vary in size,
but it does not have distinct castes like
Camponotus.
Field ants love homopteran
honeydew and are effective at driving
away biological control13. They are a key
factor in outbreaks of aphids, mealybugs,
soft scale, and other pests in many tree
and vine crops. They also feed at peach
nectaries6 and pick up the “sugar balls”
made by grape leaves. Vetch with
nectaries planted between grape rows will
attract F. aerata away from the vines2.
Field ants can dig holes in fruit, at
least where they find a crack or hole
Field ant nests mounds are lopsided and not well
started. Nectarines are susceptible to ant
developed, often with multiple entrances.
damage. In grapes, these ants might slow
down rot by scrapping out the berries. I have seen serious damage to persimmons apparently
caused by F. aerata.
Kris Tollerup, working in Coachella Valley with Formica perpilosa, found that vine
mealybug disappeared when the ants were controlled19. He found evidence that the obligate
association of VMB with F. perpilosa had abiotic factors in addition to defense.
Field ants carry mealybugs to new vines and move them between vine parts such as leaves,
fruit, trunk, and roots. Sometimes field ants cover mealybugs on vines with piles of dirt pebbles
and debris. Their colonies around vine roots are a frequent mealybug overwintering site.
I have also seen these ants carrying live alate aphids on vines.
Field ants seem to corral mealybugs in convenient spots such as under grape berries or on
trunks. This might slow the spread of mealybugs out over the vines.
Field ants prey on both pests and other predators. F. aerata is a key natural enemy of peach
twig borer in almonds and peaches6. However oriental fruit moth worms have a spitting defense
against the ants7. Field ants eat loopers on weeds (Pers. comm. Don Thomas) and carry
leafhoppers off almond trees. They will pull apart spiders such as Pardosa and Trachelas, and
wrestle down bees they can catch.
Some Formica species are such effective caterpillar predators that they have been
manipulated as biocontrol agents. Two species have been artificially established in European
timber plantations, including F. lugubris which was also successfully transferred to eastern
Canada (probably no longer allowable under
stricter regulations). During outbreaks of the pine
beauty moth on Europe, “green islands” surround
colonies of F. polyctena.
Some aphid parasites (Aphidiidae) seem to
like field ants. I have seen them hopping on and
off the backs of ants nowhere near aphids, as if
they hope the ants will lead them to aphids.
F. aerata ants often war with neighboring
colonies in vineyards. Once an ant clamps its jaws
Field ants often cover mealybugs with
on a leg or antennae, it will not let go. Sometimes
piles of pebbles and debris. Sometimes
survivors will carry around severed heads still
they nest in the vines.
hanging onto their limbs. Sometimes they carry
other adult F. aerata on their backs. Perhaps this
is a sign of slaving.
Field ants sometimes try to bite people, but it does not hurt much.
F. aerata often nests at the base of a tree or vine. Sometimes they use pre-formed cracks in
dirt. There may be multiple entrances connected by tunnels close to the surface. The mounds are
not well developed.
F. aerata forages solo. They have a run-stop-run behavior, often turning. They continue
foraging even during hot times of the day.
I have observed F. aerata nuptial flights from early May through June. The alates are
brownish, similar to the workers.
Fire ant baits based on grease are not attractive to Formica. Field ants are attracted to sugar
and protein. Tollerup found that anchovy was the most attractive bait he studied18.
Unfortunately, the most effective Formica baits are not registered in agriculture18. Fire ants
compete with field ants, so controlling fire ants can allow field ants to increase6.
Honeypot Ant
Myrmecocystus mimicus
Formicinae
Honeypot ants are a little smaller than field ants and
have a red head and thorax with a much darker gaster.
They look similar to pyramid ants, but are larger and lack
the odor when crushed. The nest is distinctive with a large
entrance that appears vertical, without much mound. They
typically nest in the open. The workers forage individually
and have a walk-sprint-walk habit.
M. mimicus tends homopterans including soft scale.
Their nests are usually outside of vineyards, but their trails
can extend at least 13 yards to vines inside. In my opinion
they are not very effective at protecting against natural
enemies.
M. mimicus preys on insects
including termites and bugs1. They
will also steal prey from harvester
ants10.
I have observed M. mimicus
nuptial flights from late March to
early May. The all-dark males are a
little larger than the workers. The
females are much larger with a red
head.
Honeypot ant worker.
Honeypot ant holes are easily recognized by their wide,
vertical entrance.
Crazy Ant
Nylanderia vividula
Formicinae
Crazy ants can be confused with Argentine ants,
which are about the same size and color. Nylanderia
vividula forages solo without distinct trails. The dark
hairs may be visible with a hand lens. The thorax is
often distinctly lighter than the gaster and head. The
scape is twice as long as the head. Tapinoma sessile
is darker and has a pungent odor when crushed.
N. vividula is native to southern United States
but has spread to other continents. It is a household
pest3. The name comes from their jerky movements
Crazy ant worker. Note the distinct hairs.
and crazy running when disturbed.
.
N. vividula is usually found tending homopterans, such as mealybugs on grapes and aphids
on pears. They seem to be less effective than field ants at guarding. I found one in an almond on
the ground. They are fairly common, but the nests are hidden . I have found this ant in Madera,
Fresno, and Tulare counties.
Little Black Ant
Monomorium minimum
Myrmicinae
This extremely small ant is easily overlooked, so
it is probably more common than reported. I have
only seen it in one location, a raisin vineyard near
Caruthers. It was tending vine mealybug.
The little black ant is an invasive species that can
be an urban pest17. It preys on insects in addition to
tending homopterans17.
Little black ant worker.
Photo by Ben Coulter.
California Harvester Ant
Pogonomyrmex californicus
Myrmicinae
This ant is the largest of our common
agricultural species. It is usually all red, although
the gaster may be darker. It is very abundant in
sandy areas but is much less common elsewhere.
For example, I have not found any in the area
around Earlimart.
Harvester ants primarily eat seeds24. They will
pick up bits of almond, but they are unable to chew
holes in intact nuts, so they are not pests of
California harvester ant worker.
Photo by Lynn Monroe
almonds.
Harvesters prey on live insects and
scavenge dead insects. I have seen them
kill honey bees and an alate of another
ant species. They eagerly scavenge on
dead birds and mammals.
Harvesters are among the few ants
which do not tend homopterans for
honeydew.
I saw a mid-size wasp with yellow
markings, probably Sphecidae, grab a
harvester ant, land on grass for a short
time, then fly off with its prey.
Harvesters build a large crescentshaped mound. The entrance has a
shallow slope making the ants all exit
on one side. Harvesters remain active
in the hot hours of the day.
According to the Wheelers23, P.
californicus is quick to inflict a very
painful sting. The pain spreads beyond
the sting site through the lymph system
The nest entrance is almost horizontal. The ants exit in
to points such as the groin and jaws.
one direction, making a lopsided mound.
The ache can last 5 hours, and swelling
and itching up to a day.
I have observed nuptial flights in June and early July.
Jet Black Harvester Ant
Messor pergandei
Myrmicinae
In 2005 I saw black harvester ants in an almond orchard north of Delano. I did not collect
them but a good guess is that they were Messor pergandei. This species is common in the
southern desserts of California and Arizona, and has been reported in the Bakersfield area.
Haney lists them as Veromessor pergandei9.
Red Imported Fire Ant (RIFA)
Solenopsis invicta
Myrmicinae
This species from South America is a major pest over much of the American south20. It has
been found in the San Joaquin Valley, but so far the counties have done a good job of quarantine
and extermination.
S. invicta looks and acts very similar to the southern fire ant, S. xyloni. Mature mounds may
be larger, and the ants are even more aggressive. Under magnification S. invicta is distinguished
by a longer scape which reaches to near the top corner of the face, four mandibular teeth instead
of three, and a third tooth in the middle of the edge of the clypeus20.
Compare also to pyramid ants, which have only one segment in the pedicel.
The value of S. invicta as a beneficial predator has been demonstrated in sugar cane and
cotton21. It did little harm to other predators. But it also defends homopteran pests.
RIFA worker.
Photo by Jon Hart
RIFA worker face showing 3 teeth on the
edge of the clypeus. S. xyloni lacks the
middle tooth. RIFA also has longer
antennae.
Photo by Mario David Bazan
Thief Ant
Solenopsis molesta
Myrmicinae
Thief ants are so named because they often co-inhabit other ant nests and steal food. They
will also consume host ant larvae and pupae17. Their diet is similar to fire ants and includes fats
and oils, as well as high-protein foods.
These tiny ants could easily be overlooked on grape vines except when they appear in mass
to feed on the sap oozing from grape girdling wounds. They are fairly common but only seen by
people who are searching under bark.
Thief ants tend mealybugs, but it is not clear how well they defend them from predators and
parasites.
They are distinguished by their tiny size and reddish yellow color.
Thief ant worker.
Thief ants massed on recent girdling wounds.
Southern Fire Ant
Solenopsis xyloni – southern fire ant
Myrmicinae
The very common southern fire ant is our most
important pest of almonds; a very effective defender of
homopteran pests; capable of harming young trees and
vines22; and our ant most guilty of biting and stinging
humans.
When fire ant nests are disturbed, the denizens rush
Southern fire ant worker.
out to attack. The workers come in a range of sizes; the
larger ones serve especially as defensive
soldiers, but all sizes fiercely sting and
bite. It is a rare SJV resident who has not
been victimized. Luckily, the pain is
usually short-lived.
Similar looking ants include pyramid
ants and Guinea groove-headed ants. Fire
ants can be distinguished by their
aggressive behavior, their large variation
in size, colony appearance, and anatomy
details covered under the other species.
In my experience fire ants are the
most successful, after Argentine ants, at
defending homopterans against predators
and parasites. In vineyards where natural
enemies have controlled most mealybugs,
fires will often be found protecting the
remaining infested vines.
In grapes, where baiting is aimed at
enabling biological control of mealybugs,
application should be early in the season.
Natural enemies need time to work.
Fire ant nests usually have multiple entrances.
Also, the ants like to corral the
mealybugs into small areas, such as between grape bunches and wood. If ant control comes late,
the mealybugs may be released to spread out in the bunch.
Only fire ants and pavement ants are almond pests, and fire ants are more common in our
orchards. They readily chew holes in nuts on the ground, and may even climb trees and eat the
nuts there. For this reason, most agricultural ant baits are aimed at fire ants. As a “grease ant”,
fires are attracted to vegetable oils, which are a typical ingredient of these baits.
Except when disturbed, fire ants remain in their nests during hot hours of the day. Thus
scouting for colonies is easiest in the cool of the morning. A trowel is handy for digging up
suspected colonies. Scouts should take care not to count pyramid ants, which come in only one
size, do not swarm out when disturbed, and have a pungent odor when crushed. Field ants are
also common in almond orchards. They are larger, appear brown, vary much less in size, and are
not as aggressive.
Nests are most common in sunny areas. Sometimes fires nest
under rocks or sticks, or around the base of weeds. Most nests have
multiple entrances, and mature colonies may have multiple
interconnected mounds extending over 25 feet. Partial tunnels may
be built along cracks with the travelling ants intermittently visible
from above.
In grapes, fire ants may nest in the vine or at the base.
Fires are predators and scavengers of dead arthropods,
earthworms, and vertebrates. The related S. geminata reduced maize
weevils in corn by 98%21. But they do not prey on twig borers6.
Fires are more capable than most ants of cutting through plant
surfaces. They can girdle young citrus trees and grape vines13. They
sometimes feed on young leaves and twigs and can damage young
citrus fruit22. On grapes, they may feed on bits of cambium exposed
through holes in the bark. They also collect and store seeds14.
I have seen fire ant nuptial flights in June and early July.
Fire ant feeding on cambium
through hole in grape bark.
Fire ant mounds interconnected along soil cracks.
Workers can be seen through breaks in the tunnel roof.
Guinea Groove-Headed Ant
(AKA Tramp Ant, Pennant Ant, Pavement Ant)
Tetramorium bicarinatum
Myrmicinae
My single record of this ant was on a vine
with vine mealybugs near Fresno on May 28, 2013.
On the same vine I found pyramid ants, pavement
ants, and field ants. I think that is my record for
most ant species on a single vine.
T. bicarinatum is in the same genus as the
pavement ant, and shares the deeply grooved face.
It resembles fire ants in color and size, but it is less
aggressive, does not have the wide size variation,
and has a 12-segmented antenna with a 3-segment
club.
The common name “tramp ant” refers to
several unrelated species that travel around the
world on ships.
This invasive species can be a household pest.
Diet is omnivorous, similar to pavement ants, and
includes fruits, meats, and grease17.
Guinea groove-headed ant worker.
Photo by Graham Montgomery
Pavement Ant
Tetramorium caespitum
Myrmicinae
Pavement ants are common on farms
and also in urban areas where they are
pests14. Their black color distinguishes them
from our similar-sized ants. Argentines,
long-horned crazies, and odorous house ants
are smaller. Under magnification,
pavements are identified by the vertical
grooves on the face.
These ants move on trails in a slow
walking gait and tend to ignore disturbance.
They have stingers but are not very
aggressive to humans.
Pavement ants are the second pest of
almonds, along with fire ants. Greasy fire
ant baits also attract and control pavement
ants.
Pavements are avid tenders of
homopteran pests but do not seem to be very
Doughnut shaped pavement ant mound.
effective at defending them. Biological
control works well when they are present.
They are predators of insects and also eat seeds, fruit
and many other foods24.
Nests in the open are donut shaped, similar to
pyramid ants. Sometimes nests are at the base of vines
around the roots.
Pavement ants are displaced by Argentine ants, but
they are among the first to return when the Argentines
are controlled. They often engage in wars with
neighboring colonies in the spring24.
Sometimes the parasitic ant Anergates atratulus
takes over T. caespitum colonies, kills the queen, and
forces the workers to raise its young24. The colony lasts
a couple of years until all the pavement workers die.
I have not seen reproductive flights of pavement
Pavement ant worker carrying a pupa of
ants.
the parasitic ant species Anergates
atratulus. Photo by Claude Pilon.
Microscopic Key
Worker ants in SJV orchards and vineyards
Use AntWeb California region2 for close-up photographs.
1a Pedicel with two segments (petiole and postpetiole) between thorax and gaster. A stinger
may be present. Ocelli absent. Myrmicinae. - 9
1b Pedicel with one segment (petiole). No stinger. - 2
2a. End of abdomen with a circular opening (acidophore), usually surrounded by a fringe of hairs.
Several of our species are large. Ocelli usually present. Formicinae. - 3
2b End of abdomen with a transverse slit opening. Our species are small to medium. No ocelli.
Dolichoderinae. - 6
3a Small brown ants, about 3 mm or less. Head, thorax and antennae with long dark setae, often
paired. Ocelli present. Nylanderia vividula. Crazy ant.
3b Large species, about 6 mm or longer. Thorax reddish with darker gaster. - 4
4a No fringe of hairs around acidophore. Head and thorax much redder than dark gaster. No
ocelli. – Camponotus essigi. Carpenter ant.
4b Acidophore with a fringe of hairs. Ocelli present. - 5
5a Maxillary palpi about as long as head. Head and thorax much redder than dark gaster.
Myrmecocystis mimicus. Honeypot ant.
5b Maxillary palpi not much larger than mandibles. Head and thorax only a little redder than
gaster. Formica aerata. California gray field ant.
6a. Abdomen and thorax both dark brown or black. - 7
6b Thorax reddish, abdomen different colored. - 8
7a Petiole with a well-developed dorsal cone. First two antennal segments beyond scape about
the same size. Dark brown. Linepithema humile. Argentine ant.
7b Petiole with dorsal cone barely showing, hidden under gaster. First antennal segment beyond
scape longer than second. Black. Tapinoma sessile. Odorous House Ant.
8a Abdomen yellowish - Forelius pruinosus
8b Abdomen darker than thorax. Propodeum with a “pyramid”. Dorymyrmex bicolor. Pyramid
ant.
9b Small or medium sized, less than 6 mm. - 10
9a Large ants, longer than 7 mm. Typically solid red or black. Long beard-like hairs under
head. - 15
10a Face with many vertical grooves. Antennae with 12 segments and 3-segment club. - 11
10b Face without such grooves. - 12
11a Head and thorax black or dark brown like abdomen. Grooves cover face from edge to edge.
Tetramorium caespitum. Pavement ant.
11b Head and thorax reddish, abdomen darker. Groves in middle of face, with sides reticulate.
Tetramorium bicarinatum. Guinea groove-headed ant.
12a Antennae 12-segmented with 3 segment club. All black. Very tiny, less than 2 mm.
Monomorium minimum. Little black ant.
12b Antennae 10-segmented with 2 segment club. Head and thorax red or reddish. Solenopsis. 13
13a Very tiny, less than 2 mm, all yellowish red. Solenopsis molesta. Thief ant.
13b Medium size, head and thorax red, gaster darker. - 14
14a Lower edge of clypeus with two teeth, one above each mandible base. Mandible with 3
teeth. Scape ends well short of upper face corner, by length of several proximal funicular
segments. Mesopleuron generally smooth. Solenopsis xyloni. Southern fire ant.
14b Clypeus with a third tooth in the middle. Mandible with 4 teeth. Scape reaches near or
beyond upper face corner. Mesopleuron dull with striations. Solenopsis invicta. Red
imported fire ant.
15a All segments black. Messor pergandei. Jet Black Harvester Ant.
15b Head and thorax bright red. Gaster usually red, sometimes darker. Pogonomyrmex
californicus. California harvester ant.
Field Key
Ants common in SJV orchards and vineyards.
Quick checks:
Pungent odor when crushed: pyramid, odorous house, Forelius. Argentine has milder odor.
All segments black or dark brown: jet black harvester, pavement, odorous house, Argentine,
crazy, little black.
Head and thorax red, gaster much darker: California harvester (some), honeypot, carpenter,
pyramid, fire.
Head and thorax reddish brown, gaster a little darker: California gray field ant.
All red: California harvester (most).
Yellow or reddish-yellow: Forelius, thief ant.
1a
1b
1c
1d
Large ants. Majority of workers 6 mm or longer. About the size of field ants or larger. - 2
Medium ants. Majority of workers 3-5 mm. About the size of typical fire ant workers. - 5
Small ants. About 2-3 mm. About the size of Argentine ants. - 8
Tiny ants. Less than 2 mm. - 11
Large Size
2a Pedicel with 2 segments. About 8 mm. Harvester ants. -3
2b Pedicel with 1 segment. About 7 mm or smaller. – 4
3a All segments black. Messor pergandei. Jet Black Harvester Ant.
3b Head and thorax bright red. Gaster may be dark, but more often bright red. Very common.
Pogonomyrmex californicus. California harvester ant.
4a Head and thorax reddish brown, only a little less dark than gaster. Ants forage solo with a
stop-start walking gait. Nest typically with a shallow slope at entrance, often with multiple
entrances, often next to objects such as tree trunks. (Sometimes nests in vine trunks.) Some
variation in size, but no distinct castes. Very common. Formica aerata. California gray
field ant.
4b Head and thorax red with much darker gaster. No distinct castes. Ants near nest have a
walk-sprint-walk-sprint gait. Nest with a large, circular, apparently vertical entrance, usually
only one, and typically out in the open. Common. Myrmecocystis mimicus. Honeypot ant.
4c Gaster dark. Head and thorax color variable, sometimes red. Majors much larger than minor
workers. Nests in wood. Rare in SJV agriculture. Camponotus essegi. Carpenter ant.
Medium Size
5a Head, thorax, and gaster black or dark. - 6
5b Head and thorax reddish, gaster darker. - 7
6a Pedicel with 2 segments. No strong odor. Nest typically out in the open or next to an object.
May be tending homopterans. Common. Tetramorium caespitum. Pavement ant.
6b Pedicel with 1 segment, difficult to see because the gaster is held high. Strong odor when
crushed. Typically found in grape vines tending mealybugs. Less commonly seen.
Tapinoma sessile. Odorous House Ant.
7a Pedicel with 1 segment. Workers all about the same size. Strong odor when smashed.
Typical mound an even doughnut with a small central entrance. During active hours,
workers continuously building mound. Very common. Dorymyrmex bicolor. Pyramid ant.
7b Pedicel with 2 segments. Worker castes vary greatly in size, with smaller workers and larger
soldiers. Colonies excitable; workers rush out when disturbed. Nests often have multiple
entrances. Odor not strong. Very common. Solenopsis xyloni. Southern fire ant.
(Mature nests of Solenopsis invicta, Red imported fire ant, may be larger and higher than
for S. xyloni, and the workers even more aggressive. See microscope key to distinguish
these two.)
Small Size
(These have 1-segmented pedicel)
8a Red with yellow gaster. Nest typically in the open. Strong odor when crushed. Often
foraging in grass or straw, with ants following distinct trails like Argentine ants. Forelius
pruinosus.
8b Dark brown or black, or gaster darker. – 9
9a Pungent odor when crushed. Almost solid black. Petiole small and hidden beneath gaster.
Tapinoma sessile. Odorous House Ant.
9b Mild odor at most. Dark brown. Petiole large and easy to see. - 10
10a Ants move between nests or forage on distinct trails which may climb vines or trees. Nests
on open ground or beneath objects. Scape reaches near top of head. Very few dark hairs on
body. Very common around houses, but in SJV typically found only on orchard or vineyard
edges, often near buildings. Mild pungent odor. Linepithema humile. Argentine ant.
10b Ants forage solo, usually on vines tending mealybugs or aphids. Scape close to twice as
long as head. Body with many long dark hairs, visible with good hand lens. Common but
not often seen except under vine or tree bark, and in buildings. Nylanderia vividula. Crazy
ant.
Tiny Size
(These have 2-segmented pedicel)
11a Reddish yellow. Common under grape bark tending mealybugs. Solenopsis molesta. Thief
ant.
11b. Black. Not as common. Typically under grape bark tending mealybugs. Monomorium
minimum. Little black ant.
Bibliography and Resources
1. American Museum of Natural History. Ants of the Southwest.
http://research.amnh.org/swrs/ants-southwest
2. AntWeb. Caltech. http://www.antweb.org/index.jsp
3. Carmean, Ingrid. 2004. Key to Most Common Ants in the Fresno Area.
http://aaie.net/wp-content/uploads/2012/12/antsCarmean.pdf.
4. Clune, Maggie. 2013. Ants catch prey - and keep it. MyScience.org.
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Battany, Neil D. Tsutsui, & Michael K. Rust. 2008. Liquid baits control Argentine
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