Blepharidatta conops

Ergatoid queens of B. conops have head disks that can be used for phragmosis, the first known case of this defensive behavior to be employed by a non-worker caste.

Identification
Kempf (1967) - Following are the characters that distinguish conops  from Blepharidatta brasiliensis: larger size; darker color; pilosity more abundant with hairs present also on ventral surface of petiole and postpetiole; clypeus with a pair of prominent tubercle; vertex with a broad sagittal furrow flanked by a pair of low and diverging ridges; occiput separated from vertex by a carina; dorsum of head lacking longitudinal rugae; occipital corners broadly and obliquely truncate and bidentate; eyes strikingly conical; antero-inferior corner of pronotum bidentate; epinotal spines relatively shorter, less approximated at base and less diverging at apex; infraspinal lamella with an upper spine and a median lobe; petiole rather cylindrical than clavate without a differentiated node; gaster entirely covered with microsculpture, never partly smooth and shining. According to Wheeler (1915: 485) brasiliensis has only 4 teeth on chewing border of mandibles. But according to my observation, both brasiliensis and conops have 5 mandibular teeth.

Distribution
Brazil. Brandão et al. (2001) - In some localities B. conops are one of the most common ants (Rosa da Silva and Brandão, 1999). It is an inhabitant of the western part of the cerrados. No B. conops specimens have never been collected in the much more well surveyed eastern cerrados, suggesting this ant species belongs to the cerrado ant fauna segment under Amazonian influence.

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil.

Biology
The following is from Brandão et al. (2001). It reports a wealth of findings regarding the biology of this species and also summarizes results from Diniz et al. (1998):

Diniz et al. (1998) observed Blepharidatta conops populations in Selvíria, MS, Brazil, and found only one wingless queen per colony. We consider these to be ergatoids because their wing buds never develop. B. conops workers forage outside the nest during daylight hours, avoiding the warmest period, although a few workers stay out of the nest all day long. Some 30–35% of the workers in each colony are foragers, searching for live arthropod prey and carcasses (mostly ants) in a circular area with an average radius of 1.5 m around the nest opening. B. conops nests are aggregated in dense populations with more than 30 nests recorded in an area of 144 m2. Mature nests take the form of an almost vertical 20 cm deep channel, not much narrower than the 2 cm diameter opening, and ending blindly in a cone-shaped widening at the bottom. In mature nests, a subsidiary horizontal chamber opens at the midlength of this main channel, where the ergatoid queen and the brood remain most of the time (Figs. 1a and b).

The 2001 study included observations of more than 100 nests in the field, from four Brazilian states, with a majority of these then brought into and housed in artificial laboratory nests for observation. Their findings include:

B. conops nests contain on average 200 workers, immatures, and a single queen. The nest structure is quite simple, consisting mainly of a blind-ended cylindrical vertical tunnel up to 20 cm deep, excavated directly in the ground, although some nests occupy spaces under the bark of fallen tree trunks. Inside the main tunnel and, especially, in the bottom enlargement, we have found grass fragments or whole blades, seeds, spider and insects corpses.

We have never found carcasses or even fragments inside the subsidiary chamber, except during the short time when the carcasses are offered to the larvae; as soon as the larvae stop feeding, the carcasses are removed (Diniz et al., 1998). Sixteen out of 26 nests excavated in Selvíria housed myrmecophile visitors either in the bottom enlargement or along the nest walls, belonging to Isopoda (6 nests), Diplopoda (6 nests), pseudoscorpion (1 nest), Lepismatidae (2 nests), Japygidae (1 nest), and Diptera larva (1 nest), either alone or in combination. Five out of the fourteen nests dissected in Serranópolis housed myrmecophile visitors, also either in the bottom enlargement or along the nest walls.

Diniz et al. (1998) described the nest development of B. conops in uniform soils. Mature nests (Fig. 1a) differ from incipient nests in that the entrances of older nests are completely surrounded by a “carcasses ring”. Our recent observations in different localities have shown that nests that are constructed in non-uniform or rocky soils (Fig. 1b) differ from nests excavated in uniform soils in being more irregular in shape. Nests excavated in all kinds of soil are composed of a single cylindrical structure, the sum of all sections attaining also some 20 cm in depth, and, most importantly, all B. conops nests exhibit the same kind of architecture, containing a single subsidiary chamber linked to the main nest by a tunnel.

A comparative study of the composition of the carcass rings in different localities confirms that they are composed of the same material found inside the bottom enlargement of the nests, that is, mostly large pieces of arthropod corpses, as can be seen in Fig. 1 of Diniz et al. (1998). These authors have also described the frequent emigration of colonies to new nests; on average each colony moves to a new nest every 4 months. Before moving, workers excavate several provisional new nests in the vicinity of the older nest; ultimately one of these is chosen, and the workers transport immatures and the queen to the new location.

As the nests mature, workers prepare or select fine-grained debris, mainly very small fragments of the arthropod carcasses (coxae, antennae, etc.), and construct from this a wall at the beginning of the tunnel (wider at its superior margin than at the bottom; see Fig. 1d). At the bottom of this wall they leave a circular opening, small enough to accommodate exactly the queen’s frontal disk (Fig. 1c). The structure and composition of the carcass wall is unrelated to soil type; the wall is always made from relatively small pieces of carcasses, much finer than the pieces composing the entrance ring or those found at the nest bottom enlargement. The position of this wall within the nests does not facilitate direct observation of ergatoid behaviour, but our indirect evidence suggests the ergatoid queen blocks the entrance to the chamber with her very much-modified frontal disk.

After construction of the carcass walls in both laboratory nests, the queens were never seen outside the subsidiary chambers, while in nests where the walls were not constructed or were incomplete, ergatoid queens frequently visited the main tunnel. The queens in wall bearing nests were observed beneath the carcass walls for long periods, that is, they could not be seen at the subsidiary chamber; as said before, the artificial nest structure prevented direct observation in these instances. The shape and diameter of the wall passage matches the shape and diameter of the queen’s frontal disk, as will be explained below. In Figs.1c and d we present our interpretation of the “carcass wall” structure and how the queens block the entrance of the chamber.

Figure 3a presents an scanning electron micrograph of the frontal disk of a queen collected in Campinaçu in frontal view. Note that the anterior slope of the pronotum and head disk share the same sculpturing pattern. In Fig. 3b, we present a scanning electron micrograph of the anterior end of a queen collected in Selvíria, in side view, showing the compound eyes (not visible in the frontal view), the extreme enlargement of the frontal carinae over the antennal scrobe, and the shape of ther head and pronotal margins (respectively anterior and posterior) that enables the head to lock against the pronotal anteroventral face. The similarly sized, regularly spaced, stiff hairs protruding laterally from the perimeter of the head and pronotum anterior slope may help the queens to keep the anterior end in position while blocking the entrance of the tunnel.

Queens from different localities differ not only in size, but also in the sculpture of the frontal disk, although in a given population the ergatoids are very similar to one another. Workers and males from the different localities do not differ so dramatically.

Nests release males from August to February (Diniz, unpub. field observations), although in laboratory colonies males are produced year round. On one occasion we found a dealate male inside the main tunnel of a field nest – a syndrome often associated with nomadic ant species (Hölldobler and Wilson, 1990). In the laboratory, males actively search for nests, and, when close enough, are brought inside by groups of workers. We have never observed more than one male in a nest at a time. Inside the nest the male is groomed by workers and meets the virgin queen near the nest entrance, where copulation takes place.

Nests often house one or more myrmecophiles. In five out of 26 nests excavated in Selvíria we found larvae and adult Histeridae beetles either in the bottom enlargement or along the nest walls; in addition to histerids, two of the nests also contained pseudoscorpions and diplopods (Diniz, 1994). B. conops larvae are held in the mandibles of the workers positioned along the nest wall or laid on the floor of the subsidiary chamber, but are never found in the widened bottom chamber. B. conops workers feed their larvae by trophallaxis, after chewing the corpses or fragments of the arthropod prey and some vegetal material. Diniz (1994) observed histerid beetles taking full grown larvae from workers’ mandibles. The recovery of larvae by the workers is made impossible by the beetles’ behaviour; after “stealing” a larva, a beetle “crouches” over it, bending its legs under the carapace, and thus assuming the format of an almost perfect half sphere. The beetles’ smooth integument prevents their removal from the nest by the ants.

Queens actively walk throughout the nests. However, in nests where we found myrmecophiles such as histerid beetles, the majority of the ants immatures were located in the subsidiary chamber. In the presence of predators, the queen uses her extremely modified anterior end to block the entrance of the tunnel wall that leads to the subsidiary chamber, preventing the predators from reaching the brood (Fig. 1b). The diameter of the opening in the wall is fitted to the ergatoid queen’s frontal disk.

Nomenclature

 *  conops. Blepharidatta conops Kempf, 1967d: 355, figs. 4, 5 (w.) BRAZIL. See also: Diniz, Brandão & Yamamoto, 1998: 270.

Worker
(holotype). - Total length 4.4 mm; maximum length of head capsule 1.12 mm; maximum width of head (eyes excluded) 0.93 mm; scape length 0.77 mm; maximum diameter of eyes 0.13 mm; Weber's length of thorax 1.23 mm; hind femur length 1.07 mm; petiole length 0.72 mm; petiole width 0.24 mm. Dark reddish brown; legs and gaster chestnut brown. Integument opaque, finely and densely reticulate-punctate throughout, with a silky sheen. Microsculpture of gaster rather superficial, therefore somewhat shining.

Head. Mandibles finely striate; chewing border with 5 teeth, apical and subapical teeth (often worn off) stronger than basal ones, prominent, pointed. Anterior border of clypeus convex; central portion perpendicular, shallowly concave, basal half laterally marginate, the margination ending above in a prominent tubercle or blunt tooth; posterior portion grading into the dorsal face of head with convex and distinct posterior border. Frontal area distinct and impressed. Frontal carinae greatly expanded laterad, covering the sides of head in dorsal view, their lateral border coarsely crenate; just inside the border runs a longitudinal ridge. Dorsum of head with a sagittal impression, broadening caudad and flanked by a pair of diverging, blunt and low ridges, each one sending out laterad two or three very faint transverse ridges. Occiput separated from vertex by an oblique irregular ridge or carina which becomes obsolete in the middle. Occipital corners obliquely truncate, prominent, bearing laterad a blunt excised lobe, mesad a small tooth. Occipital border deeply excised, with a prominent convex lobe in the middle. Antennal scrobe covered by the frontal carinae, deep, attaining the occipital corner, margined below by a carinule running from the occipital corner to above the eye, with another carinule branching off somewhat behind the eye and terminating below it. Cheeks sparsely, coarsely and irregularly rugose, lower border sharply marginate. Gular face and antennal scrobe without macrosculpture, nearly smooth. Eyes conical, unusually prominent, their depth subequal to their width at base. Scape slender, apically gently incrassate, reaching the apex of the scrobe when lodged in it. Funicular segments: I twice as long as broad, II-VII scarcely longer than broad, VIII slightly, IX conspicuously, X strikingly elongate.

Thorax. Pronotum with a prominent scapular and posterior tubercle on each side; a similar tubercle, yet fainter, projecting laterad from mesonotum. Dorsal sutures on thorax absent. Antero-inferior angle of pronotum bidentate. Mesopleura with a prominent, triangular, foliaceous lobe anteriorly, projecting forward, laterad of anterior coxae. Epinotum laterally sharply marginate on base, with very long, thin, acute, scarcely raised and little diverging spines, with a prominent infraspinal lamella marginating the declivous face; this infraspinal lamella bears dorsally another small spine, below it a rounded lobe and at the bottom a rectangular tooth. Dorsum and sides of thorax with heavy, irregular ridges and rugae, lacking on epinotum. Basal and declivous face of epinotum separated from each other by a transverse carinule which is narrowly interrupted in the middle. Legs rather long, sharply and finely punctate; femora only gently incrassate; hind tibiae scarcely longer than tarsite I of the same leg.

Pedicel. Petiole elongate, subcylindrical, anteriorly slightly attenuate both in dorsal and side view. Anteroventrally with a small denticle. Postpetiole in dorsal view subquadrate, scarcely broader than long, its sides straight and subparallel. Both segments irregularly rugose, but less coarsely so than on thorax. Gaster elliptical, narrowly truncated in front.

Pilosity: numerous long, bristly, standing hairs on dorsum of head, thorax, pedicel and gaster; similar hairs, but conspicuously shorter and scarcer on ventral face of petiole, postpetiole and gaster. Fore coxae with a few long standing hairs projecting from the anterior face. Antennae and legs with shorter, rather dense and oblique hairs. Fringing hairs of frontal carinae.

All six specimens are practically alike. The size variation is very little. The holotype is the smallest of the series. The largest specimens measures as follows: Total length 4.6 mm; head length 1.17 mm; head width (without eyes) 0.96 mm; Weber's length of thorax 1.30 mm; petiole length 0.75 mm; petiole width 0.27 mm.

Type Material
6 workers (holotype and paratypes) from Fazenda Retiro de Telhas, Tres Lagoas, Mato Grosso State, Brazil, taken on May 28, 1964 by Karol Lenko, who discovered them at day time walking on the ground in a xerophilous forest of the savanna type callee! locally «cerradao». Holotype and 2 paratypes deposited in the collection of the Departamento de Zoologia, Sao Paulo (DZSP), the remaining paratypes in my private collection (WWK).