|
The subfamily Dolichoderinae is best
represented in tropical areas, where there are many genera and species.
Relatively few have penetrated into temperate zones and fewer still
into the arid desert. The species which do occur in our area include
two which are present only marginally, one introduced species and
several wide-ranging forms tolerant of diverse conditions.
Dolichoderines share with the subfamily
Formicinae a one-segmented petiole. The most conspicuous morphological
difference between the two groups is the presence of an acidopore
among the formicines. Instead of an acidopore, the dolichoderines
possess only an anal slit. Both groups lack a sting so defense of
colonies and individuals must rely upon other deterrent methods.
These two subfamilies employ chemical defenses. Formicines, as a
whole, utilize a chemical defense which is partially, or entirely,
formic acid. Female castes of our species of formicines will, when
their gasters are crushed, yield the characteristic sharp odor of
formic acid.
In the dolichoderine ants the compounds
of defense are centered around cyclopentanoid monoterpenes. These
compounds are quite aromatic and, to humans anyway, very disagreeable.
The odor has been variously compared to rancid butter, rotting coconuts
and scorched rubber. Whatever the comparison, these compounds are
convincingly repugnant and provide an excellent field identification
characteristic.
Colonies of Liometopum,
Tapinoma, and Forelius are usually quite large and numerous
females are present. Those of Dorymyrmex are evidently smaller and
may have only a single female. With the exception of Tapinoma,
however, none of these has been extensively studied. The dolichoderines
as a group are quite aggressive omnivores. Forelius, Liometopum,
and Forelius are all trail foragers. In Dorymyrmex
trails are less consistent and when they do occur, do not receive
the heavy traffic so characteristic of the others.
Since our fauna includes so few species
of Dolichoderinae, the following keys are for both genera
and species, except that in the key to males no effort is made to
separate those of the two Forelius species or the three Dorymyrmex.
KEY
TO GENERA AND SPECIES OF DOLICHODERINAE
workers & queens
|
| 1 |
Juncture of basal and posterior faces of worker propodeum rounded,
not produced upward as a conical process in lateral view (Figs.
196, 198, 200); segment 3 of maxillary palpus distinctly shorter
than following three combined |
2 |
| -- |
Juncture of basal and posterior faces of worker propodeum, in
profile, conically produced upward (Fig. 202); segment 3 of
maxillary palpus longer than following three combined (Fig.
6) (Dorymyrmex) |
6 |
| 2
(1) |
Worker monomorphic; gastral terga without appressed dense, long
grayish pubescence; gap between lateral margin of clypeus and
base of mandible very narrow (Fig. 195a) |
3 |
| -- |
Worker polymorphic; gastral terga with appressed dense, long
grayish pubescence; gap between lateral margin of clypeus and
mandibular base large (Fig. 191a) |
Liometopum occidentale
Wheeler |
| 3
(2) |
Frons and dorsum of mesosoma with at least several long erect
setae; petiolar scale small, distinct, erect or suberect (Figs.
198, 200) |
4 |
| -- |
Frons and dorsum of mesosoma without erect setae; petiolar scale
small, strongly inclined forward, adnate to anterior peduncle
(Fig. 196) |
Tapinoma sessile (Say)
|
| 4(3)
|
Ventral margin of clypeus thin, without median beveled area;
mandible with four distinct, close teeth and a weak basal tooth,
denticles present only between basal and subbasal teeth; worker
metanotum not depressed below base of propodeum, latter flat
(Forelius) |
5
|
| --
|
Ventral
margin of clypeus thick, with median, triangular beveled area;
mandible with four or five widely spaced teeth, with several
minute denticles between each (except apical and preapical teeth);
metanotum of worker sharply depressed below level of anterior
margin of propodeal base, latter strongly convex |
Linepithema humile
(Mayr) |
| 5
(4) |
5(4) Antennal scape and all tibiae with at least a few suberect
to erect hairs; vertex corner with a few short erect hairs;
worker pronotum with 6 or more erect hairs (Figs. 198, 199) |
F. mccooki (Forel) |
| -- |
--
Scape, tibiae and vertex corner without erect hairs; worker
pronotum with 2 or 4 erect hairs (Figs. 200, 201) |
F. analis (André)
|
| 6(1) |
Head, mesosoma and gaster concolorous, from yellowish to blackish
brown. Worker: interocular distance less than 1.5 times EL;
CI less than 95 (Fig. 204) |
7 |
| -- |
Head
and mesosoma ferruginous, gaster brownish black. Worker: interocular
distance more than 1.5 time EL; CI over 95 (Fig. 203) |
D. bicolor Wheeler |
| 7(6) |
Mesonotum, in profile, distinctly broadly angulate at about
posterior two-thirds so that there are two distinct surfaces
(Figs. 00, 00) |
8 |
| --
|
Mesonotal
profile more or less evenly curved and without angulation posteriorly
(Figs. 00, 00) |
9 |
| 8(7) |
Color light to very dark brownish, head and gaster commonly
darker than mesosoma; pronotal seta pair usually present
|
D. insanus (Buckley) |
| --
|
Color
clear yellowish to reddish yellow, often with vertex, mesosomal
dorsum, and apex of gaster infuscated; pronotal seta pair commonly
absent |
D. flavus McCook |
| 9(7) |
Mesonotum weakly curved in profile (Fig. 00); eyes exceptionally
large, IOR ca. 115; head and gaster brown, distinctly darker
than mesosoma |
D. species 2 |
| -- |
Mesosoma strongly convex in profile (Fig. 00); eyes not exceptionally
large, IOR ca. 128; head and mesosoma concolorous yellowish
red, gaster mostly dull brownish |
D. species1 |
| |
Males
|
|
| 1 |
Scape much longer than second flagellar segment (Figs. 197,
205) |
2
|
| -- |
-- Second flagellar segment distinctly longer than scape |
Linepithema
humile (Mayr) |
| 2(1)
|
Segment 3 maxillary palpus about as long as second, much shorter
than combined lengths of last three; head flattened in profile
or not |
3 |
| -- |
Segment 3 of maxillary palpus much longer than second, about
equal to combined lengths of last three; head distinctly flattened
in profile (Fig. 205) |
Dorymyrmex spp. |
| 3(2) |
Scape shorter than combined lengths of next four segments; base
of gaster without impressed area for reception of petiole; erect
body hairs often abundant |
4 |
| -- |
Scape about as long as combined lengths of next five segments
(fig. 197); base of gaster with impressed area for reception
of petiole; erect body hairs sparse |
Tapinoma sessile (Say)
|
| 4(3) |
Head distinctly flattened, more or less concave beneath; body
hairs sparse; length less than 4 mm |
Forelius
spp. |
| --
|
Head
convex anteriorly and posteriorly (Fig. 194); body hairs abundant;
length 7-11 mm |
Liometopum
occidentale Wheeler |
|