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.