Identification and Habits
of Key Ant Pests in the
Pacific Northwest
Ants (Hymenoptera: Formicidae) are an easily
recognized group of social insects. The workers
are wingless, have elbowed antennae, and have a
petiole (narrow constriction) of one or two segments
between the mesosoma (middle section) and the
gaster (last section) (Fig. 1).
Ants are one of the most common and abundant
insects. A 1990 count revealed 8,800 species of ants
had been described and that number has increased
to more than 14,000. There are still a number of
undescribed ant species in the world. The true
number is probably more than 30,000.
Ants are also one of the most widely distributed
of all insect groups. They occur from the Arctic
tree line to the humid tropics, from Alaska to the
extreme tip of South America, to the tip of Africa,
Australia, and even to all the islands in the oceans.
They are the most abundant of all social insects.
Since there are so many species of ants, and in such
diverse habitats, it becomes obvious that ants are
one of humans’ principal insect competitors. Ants
infest buildings as a nuisance, feed on human foods,
and even cause structural damage.
Ants are also annoying because of their biting or
stinging habits. Ant stings are responsible for a
number of human fatalities in the United States
each year. The effects of stings on a human depend
on the ant species and the sensitivity of the person.
Most deaths are caused by a hypersensitive reaction
leading to anaphylactic shock.
General Biology
Many ant colonies are started by a single
inseminated female, called a queen. From this
single individual, ant colonies can grow to contain
anywhere from several hundred to millions of
individuals. Among the largest ant colonies are
the army ants of the American tropics, with up
to several million workers, and the driver ants of
Africa, with 30 million to 40 million workers. A
thatching ant (Formica) colony in Japan covering
many acres was estimated to have 348 million
workers. However, most ant colonies probably fall
within the range of 300 to 50,000 individuals.
Ants normally have three distinct castes: males,
queens, and workers. Males are intermediate in size
between queens and workers and can be recognized
by ocelli (simple eyes) on top of the head, wings,
protruding genitalia, and large eyes. The sole
function of the male is to mate with a winged
female during the nuptial flight.
The winged female loses her wings soon after
mating and becomes a queen. However, scars where
the wings were attached remain. Queens usually also
have ocelli in addition to large compound eyes and
a large gaster for egg production.
The worker, the smallest member of the colony,
usually lacks ocelli and is never winged. Workers of
a single species may be of one size (monomorphic)
or may vary considerably in size (polymorphic).
Large workers are usually called soldiers or majors;
very small workers are minors.
Ants pass through several distinct developmental
stages in the colony: egg, larva, pupa, and adult.
The egg is very small (less than 1 mm) and varies
in shape according to species. The larva also varies
in size and shape, but is usually white and is always
legless. The pupal stage looks like the adult, but
is soft, white, and motionless; many species are
enclosed in a cocoon of a brownish or whitish
papery material produced by the mature larva.
2
Ants produce winged reproductives usually at one
time of the year (spring or fall, depending on species
and colony disposition). Colony activity at the
time of reproductive swarming is high. The winged
females and males fly from colonies and mate, and
shortly afterward the male dies. The inseminated
queen then builds a small nest, lays a few eggs, and
nurtures the developing larvae that soon hatch from
the eggs. When adult workers appear, they take over
the function of caring for the queen and the larvae,
building the nest, and bringing in food for the
colony. Colonies of some species may persist for 20
years or more.
Since there are so many species of ants with
extremely diverse habits it is difficult to outline a
common lifestyle. Some ants are strictly carnivorous,
while others may specialize by eating fungi, seeds,
or the “honeydew” of other insects. However, most
ants that cause annoyance to homeowners are
omnivorous and feed on a variety of foodstuffs.
Various ants make their nests in rotting logs, trees,
soil, or even live inside the nests of other ants.
Since they are such a diverse group, it is always best
to check the habits of the particular species. Ants
that are common in the Pacific Northwest states
of Washington, Idaho, and Oregon occur in and
around structures are presented in this publication.
Identification
Ants are often confused with termites by
homeowners. Consider the following features to
separate ants from termites:
Ants
1. Strong constriction petiole or “waist” between
mesosoma and gaster (Fig. 1a).
2. Elbowed antennae (Fig. 1a).
3. Forewing, when present, much larger than
hindwing (Fig. 1b).
4. Workers are various colors and hard-bodied.
Termites
1. Abdomen broadly joined to thorax (no waist)
(Fig. 2a).
Forewing
Hindwing
b
a
Head Mesosoma
Petiole
Gaster
Elbowed Antenna
Node
Acidopore
Thorax Abdomen
Broadly jointed waist
Straight
antenna
a
Forewing
Hindwing
b
Fig. 1. (a) Profile of worker ant; (b) wings from a reproductive
ant.
Fig. 2. (a) Profile of a worker termite; (b) wings from a
reproductive termite.
3
2. Straight antennae (Fig. 2a).
3. Both pairs of wings, when present, of about
equal size (Fig. 2b).
4. Workers are whitish and soft-bodied.
Ants in the Pacific Northwest that occur around
structures are included in four subfamilies of ants:
1. Formicinae: carpenter ants, thatching ants,
moisture ants, and small honey ants
2. Dolichodorinae: odorous house ants and velvety
tree ants
Key to workers
(identifying many of the characteristics will require use of a hand lens)
1) Abdominal petiole composed of one segment (Fig. 3a) .......................................................................... 2
Abdominal petiole composed of two segments (Fig. 3b) (Subfamily Myrmicinae)................................... 8
2) Node broad at the apex, rectangular (Fig. 4) (Subfamily Ponerinae) ..................Hypoponera punctatissima
Node not broad at the apex, flattened or pointed (Fig. 1) ...................................................................... 3
3) Tip of gaster with circular acidopore (opening) usually surrounded by a fringe of hairs (Fig. 5a)
(Subfamily Formicinae)........................................................................................................................... 4
Opening at the end of the gaster slit-shaped, not surrounded by hairs (Fig. 5b)
(Subfamily Dolichoderinae)..................................................................................................................... 7
4) Profile of thoracic dorsum evenly convex (Fig. 6a) ..................................carpenter ants, Camponotus spp.
Profile of thoracic dorsum not evenly convex, with notch (Fig. 6b)......................................................... 5
5) Epinotal spiracle a narrow slit (Fig. 7a)...........................................................thatching ants, Formica spp.
Epinotal spiracle rounded (Fig. 7b) ......................................................................................................... 6
6) Scape surpassing occipital margin by less than one-third its length (Fig. 8a)......moisture ants, Lasius spp.
Scape surpassing occipital margin by at least one-third its length (Fig. 8b)
...........................................................................................................small honey ants, Prenolepis imparis
7) Node on pedicel flattened when viewed in profile (Fig. 9a)...............odorous house ants, Tapinoma sessile
Node on pedicel vertical when viewed in profile (Fig. 9b).................... velvety tree ants, Liometopum spp.
8) Antenna with 10 segments (Fig. 10a) ........................................................... thief ants, Solenopsis molesta
Antenna with more than 10 segments (Fig. 10b).................................................................................... 9
9) Spines on the epinotum (Fig. 11a)........................................................................................................ 10
No spines on the epinotum (Fig. 11b) ............................................ pharaoh ants, Monomorium pharaonis
10) Rows of long hairs on underside of head (psammophore) (Fig. 12)
........................................................................................................... harvester ants, Pogonomyrmex spp.
Short hairs on the underside of head, no psammophore....................................................................... 11
11) Dorsal profile of the mesosoma markedly step-like (Fig. 13a).......................................Aphaenogaster spp.
Dorsal profile of the mesosoma even or only slightly indented (Fig. 13b)
.............................................................................................................. pavement ants, Tetramorium spp.
3. Myrmicinae: pharaoh ants, little black ants,
pavement ants, harvester ants, Aphaenogaster spp.
4. Ponerinae: ponerine ants
The following keys will assist in the identification
of common household ants recorded as pests in the
Pacific Northwest.
Note: The first key is for workers. Additional keys
are provided for winged females and males. In
selecting worker ants for the key, select the largest
ants available.
4
Fig. 3. Profile of abdominal pedicel. (a) One-segment; (b) twosegments.
Fig. 4. Profile of pedicel and gaster of Hypoponera
punctatissima.
a b
Fig. 5. Profile and ventral views of tip of gaster. (a)
Camponotus spp. (arrow: acidopore); (b) Liometopum spp.
(arrow: transverse, slit-like opening).
a b
Fig. 6. Mesosoma profile. (a) Camponotus spp.; (b) Lasius
spp.
Fig. 7. Profile of epinotum and pedicel. (a)
Identification and Habitsof Key Ant Pests in thePacific NorthwestAnts (Hymenoptera: Formicidae) are an easilyrecognized group of social insects. The workersare wingless, have elbowed antennae, and have apetiole (narrow constriction) of one or two segmentsbetween the mesosoma (middle section) and thegaster (last section) (Fig. 1).Ants are one of the most common and abundantinsects. A 1990 count revealed 8,800 species of antshad been described and that number has increasedto more than 14,000. There are still a number ofundescribed ant species in the world. The truenumber is probably more than 30,000.Ants are also one of the most widely distributedof all insect groups. They occur from the Arctictree line to the humid tropics, from Alaska to theextreme tip of South America, to the tip of Africa,Australia, and even to all the islands in the oceans.They are the most abundant of all social insects.Since there are so many species of ants, and in suchdiverse habitats, it becomes obvious that ants areone of humans’ principal insect competitors. Antsinfest buildings as a nuisance, feed on human foods,and even cause structural damage.Ants are also annoying because of their biting orstinging habits. Ant stings are responsible for anumber of human fatalities in the United Stateseach year. The effects of stings on a human dependon the ant species and the sensitivity of the person.Most deaths are caused by a hypersensitive reactionleading to anaphylactic shock.General BiologyMany ant colonies are started by a singleinseminated female, called a queen. From thissingle individual, ant colonies can grow to containanywhere from several hundred to millions ofindividuals. Among the largest ant colonies arethe army ants of the American tropics, with upto several million workers, and the driver ants ofAfrica, with 30 million to 40 million workers. Athatching ant (Formica) colony in Japan coveringmany acres was estimated to have 348 millionworkers. However, most ant colonies probably fallwithin the range of 300 to 50,000 individuals.Ants normally have three distinct castes: males,queens, and workers. Males are intermediate in sizebetween queens and workers and can be recognizedby ocelli (simple eyes) on top of the head, wings,protruding genitalia, and large eyes. The solefunction of the male is to mate with a wingedfemale during the nuptial flight.The winged female loses her wings soon aftermating and becomes a queen. However, scars wherethe wings were attached remain. Queens usually alsohave ocelli in addition to large compound eyes anda large gaster for egg production.The worker, the smallest member of the colony,usually lacks ocelli and is never winged. Workers ofa single species may be of one size (monomorphic)or may vary considerably in size (polymorphic).Large workers are usually called soldiers or majors;very small workers are minors.Ants pass through several distinct developmentalstages in the colony: egg, larva, pupa, and adult.The egg is very small (less than 1 mm) and variesin shape according to species. The larva also variesin size and shape, but is usually white and is alwayslegless. The pupal stage looks like the adult, butis soft, white, and motionless; many species areenclosed in a cocoon of a brownish or whitishpapery material produced by the mature larva.2Ants produce winged reproductives usually at onetime of the year (spring or fall, depending on speciesand colony disposition). Colony activity at thetime of reproductive swarming is high. The wingedfemales and males fly from colonies and mate, andshortly afterward the male dies. The inseminatedqueen then builds a small nest, lays a few eggs, andnurtures the developing larvae that soon hatch fromthe eggs. When adult workers appear, they take overthe function of caring for the queen and the larvae,building the nest, and bringing in food for thecolony. Colonies of some species may persist for 20years or more.Since there are so many species of ants withextremely diverse habits it is difficult to outline acommon lifestyle. Some ants are strictly carnivorous,while others may specialize by eating fungi, seeds,or the “honeydew” of other insects. However, mostants that cause annoyance to homeowners areomnivorous and feed on a variety of foodstuffs.Various ants make their nests in rotting logs, trees,soil, or even live inside the nests of other ants.
Since they are such a diverse group, it is always best
to check the habits of the particular species. Ants
that are common in the Pacific Northwest states
of Washington, Idaho, and Oregon occur in and
around structures are presented in this publication.
Identification
Ants are often confused with termites by
homeowners. Consider the following features to
separate ants from termites:
Ants
1. Strong constriction petiole or “waist” between
mesosoma and gaster (Fig. 1a).
2. Elbowed antennae (Fig. 1a).
3. Forewing, when present, much larger than
hindwing (Fig. 1b).
4. Workers are various colors and hard-bodied.
Termites
1. Abdomen broadly joined to thorax (no waist)
(Fig. 2a).
Forewing
Hindwing
b
a
Head Mesosoma
Petiole
Gaster
Elbowed Antenna
Node
Acidopore
Thorax Abdomen
Broadly jointed waist
Straight
antenna
a
Forewing
Hindwing
b
Fig. 1. (a) Profile of worker ant; (b) wings from a reproductive
ant.
Fig. 2. (a) Profile of a worker termite; (b) wings from a
reproductive termite.
3
2. Straight antennae (Fig. 2a).
3. Both pairs of wings, when present, of about
equal size (Fig. 2b).
4. Workers are whitish and soft-bodied.
Ants in the Pacific Northwest that occur around
structures are included in four subfamilies of ants:
1. Formicinae: carpenter ants, thatching ants,
moisture ants, and small honey ants
2. Dolichodorinae: odorous house ants and velvety
tree ants
Key to workers
(identifying many of the characteristics will require use of a hand lens)
1) Abdominal petiole composed of one segment (Fig. 3a) .......................................................................... 2
Abdominal petiole composed of two segments (Fig. 3b) (Subfamily Myrmicinae)................................... 8
2) Node broad at the apex, rectangular (Fig. 4) (Subfamily Ponerinae) ..................Hypoponera punctatissima
Node not broad at the apex, flattened or pointed (Fig. 1) ...................................................................... 3
3) Tip of gaster with circular acidopore (opening) usually surrounded by a fringe of hairs (Fig. 5a)
(Subfamily Formicinae)........................................................................................................................... 4
Opening at the end of the gaster slit-shaped, not surrounded by hairs (Fig. 5b)
(Subfamily Dolichoderinae)..................................................................................................................... 7
4) Profile of thoracic dorsum evenly convex (Fig. 6a) ..................................carpenter ants, Camponotus spp.
Profile of thoracic dorsum not evenly convex, with notch (Fig. 6b)......................................................... 5
5) Epinotal spiracle a narrow slit (Fig. 7a)...........................................................thatching ants, Formica spp.
Epinotal spiracle rounded (Fig. 7b) ......................................................................................................... 6
6) Scape surpassing occipital margin by less than one-third its length (Fig. 8a)......moisture ants, Lasius spp.
Scape surpassing occipital margin by at least one-third its length (Fig. 8b)
...........................................................................................................small honey ants, Prenolepis imparis
7) Node on pedicel flattened when viewed in profile (Fig. 9a)...............odorous house ants, Tapinoma sessile
Node on pedicel vertical when viewed in profile (Fig. 9b).................... velvety tree ants, Liometopum spp.
8) Antenna with 10 segments (Fig. 10a) ........................................................... thief ants, Solenopsis molesta
Antenna with more than 10 segments (Fig. 10b).................................................................................... 9
9) Spines on the epinotum (Fig. 11a)........................................................................................................ 10
No spines on the epinotum (Fig. 11b) ............................................ pharaoh ants, Monomorium pharaonis
10) Rows of long hairs on underside of head (psammophore) (Fig. 12)
........................................................................................................... harvester ants, Pogonomyrmex spp.
Short hairs on the underside of head, no psammophore....................................................................... 11
11) Dorsal profile of the mesosoma markedly step-like (Fig. 13a).......................................Aphaenogaster spp.
Dorsal profile of the mesosoma even or only slightly indented (Fig. 13b)
.............................................................................................................. pavement ants, Tetramorium spp.
3. Myrmicinae: pharaoh ants, little black ants,
pavement ants, harvester ants, Aphaenogaster spp.
4. Ponerinae: ponerine ants
The following keys will assist in the identification
of common household ants recorded as pests in the
Pacific Northwest.
Note: The first key is for workers. Additional keys
are provided for winged females and males. In
selecting worker ants for the key, select the largest
ants available.
4
Fig. 3. Profile of abdominal pedicel. (a) One-segment; (b) twosegments.
Fig. 4. Profile of pedicel and gaster of Hypoponera
punctatissima.
a b
Fig. 5. Profile and ventral views of tip of gaster. (a)
Camponotus spp. (arrow: acidopore); (b) Liometopum spp.
(arrow: transverse, slit-like opening).
a b
Fig. 6. Mesosoma profile. (a) Camponotus spp.; (b) Lasius
spp.
Fig. 7. Profile of epinotum and pedicel. (a)
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