Simopelta andersoni

One of the more common Costa Rican Simopelta species.

Identification
The large eye and the four mandibular teeth would separate this species from all of the others in the genus Simopelta . It would be most likely confused with the large eyed Simopelta oculata, which only has three mandibular teeth. The transverse striae or rugulae on the dorsum of the head could result in confusion with S. transversa and similar species, all of which have three mandibular teeth. Additionally, the top of the petiolar node has distinct, transverse striae, the top of the node of S. transversa  has an indistinct, granulate sculpture.

It is closely related to Simopelta quadridentata, but differs in a number of consistent characteristics. The eye is larger, the subpetiolar process is more elongated (length at bottom of lobe > 0.1 mm, versus < 0.1 mm in S. quadridentata) and the same depth over the length (wider posteriorly in S. quadridentata). The upper part of the node of the petiole has vertical striae, which then pass transversely over the top of the node. The node of S. quadridentata has mostly horizontal striae, which encircle the node and isolate the similar transverse striae. The long, lobed process over the clypeal apron could cause confusion with Simopelta longirostris. They can be easily separated, as S. andersoni has four mandibular teeth, S. longirostris has three.

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica.

Habitat
Mountainous regions from 200-1200m elevation. This species occurs in mature montane forest habitats, with highest density around 1000m elevation.

Biology
Longino has collected and observed numerous colonies of Simopelta andersoni. Select field notes from these collections:

JTL12Sep82/1030: (Carrillo) A column was moving brood from one cache to another. The column's endpoints seemed to be the two caches, 5-10m apart. The caches were large piles of brood of uniform age. One cache was on the ground beneath dead leaves. These larvae were being carried to the second cache inside a dead Heliconia petiole, 20cm above the ground.

JTL1384: (Zona Protectora, 880m) 14 Jul: Wet forest. A column of workers led to a hole at the base of a treefern stump. Excavating yielded a cache of brood of uniform size, a few cm's in from the stump base at ground level. Many workers were escaping down a hole into the soil. I excavated about 10cm further in that direction, and unearthed a queen. She was attended by a single worker when I found her, the worker riding with head and forelegs on the queen's abdomen. There was just the single brood pile. I collected the queen, about 25 workers, and about 15 larvae alive, and took them back to La Selva for observation. They were collected into a whirlpac bag. 15 Jul: Today at 1100hrs I transferred them to a 9cm dia plastic petri dish. This involved chilling for about 10 minutes in a refrigerator. Within a few minutes the larvae had been moved to one place and the queen was standing on top of the pile. 24 Jul: Over the past several days I have twice fed ant brood to Simopelta. Workers pick up the brood and carry it to their brood. I presume they are eating it. A week ago I fed them some Pheidole fiorii brood. Yesterday I fed them brood from Pheidole dossena (collection #1428). I returned to Santa Barbara, California with the live colony. Although out of food, they ignored larvae of Camponotus dumetorum and Crematogaster ashmeadi which I had in cultivation. The workers and the queen died one by one.

JTL1488: (Penas Blancas) Forested ridge just before reaching Eladio's house. I first saw a column crossing the trail. I followed them back to where they were emerging from under a stone. The other end of the column was the leading edge, and they were slowly moving away from the rock. I turned the rock, and the entire colony was clustered tightly on the underside of the stone. There were hundreds of workers (probably less than 1000), one queen, and tiny brood. There was very little brood, and what there was was in the form of small white packets that workers carried away in their mandibles. When I turned the stone the queen was one of the first individuals to disassociate herself from the cluster. She moved about on the stone unattended for a while (10-20 seconds) and then joined the column of retreating workers that were leaving the stone. As she joined the column she acquired an attendant worker that placed its head and forelegs over her abdomen and they ran off together. The cluster at first was about 4cm wide and 1cm high. After exposure it slowly melted, as workers gradually left the outer surface of the cluster. It took over a minute for the cluster to completely dissipate. The rock surface was clean and I could closely watch the exodus. Two myrmecophiles appeared as the cluster dissolved. Early-on, a phorid fly was observed running with the workers. At the very end, as the last worker left, a small parasitic wasp remained that had been deep in the center of the cluster. The fly and the wasp were collected into a vial with the ant sample. Lubomir Masner identified the wasp as a member of the genus Doliopria in the Diapriidae. The vial also contains the remains of a dead worker of Pheidole rogeri. The dead ant was on a stick near the nest entrance, and many workers stopped and antennated it as their column passed over it.

JTL2038: (Penas Blancas) wet forest, colony migration column on trail. I collected the queen as she traveled with the column. The queen was attended by only one worker. I saw no noticeable knot of workers nor thickening of column near queen. Pheidole soldier head capsule in collection.

JTL4Jul84/1438: (Penas Blancas) wet forest, around Guindon cabin. A colony was in underground chambers on the bank of a stream in the forest. The chambers were in loose, clay soil. The colony seemed to be diffusely spread in the clay bank, extending back in about 20cm and ca.10cm below the surface. There was a single main entrance in the vertical clay bank. A raiding column was returning with booty from a Pheidole fiorii nest greater than 5m away. The raided nest was a pendant agglomeration of chambered humus-like material on two strap-shaped fern leaves. The nest hung about 1.5m above the stream. When I broke into chambers of the Simopelta nest, it appeared that dismembered booty (larvae and pupae) were scattered over the floor with feeding Simopelta larvae. An outer chamber contained a few pupae, which were in cocoons.

I collected the entire raided Pheidole nest in a plastic bag. The nest was completely abandoned. All that remained were various brood, 1 callow worker, a male, and an alate queen that was cloistered in an inner chamber, probably as yet unnoticed by the Simopelta. There was abundant queen brood in the nest, and many of the queen pupae were neatly cut up into head, trunk, and gaster, I presume in preparation for transport back to the Simopelta nest.

On examination of the collection in the lab, there seemed to be two kinds of Simopelta larvae: short pea-shaped larvae and larger, longer, curved larvae. Booty included larvae and pupae, I think of the Pheidole fiorii nest being raided. There were also two cocoons with ponerines(?) inside. They seemed too small to be Simopelta.

Nomenclature

 *  andersoni. Simopelta andersoni Mackay & Mackay, 2008: 296, figs. 6, 25, 27, 28 (w.) COSTA RICA.

Worker
The worker of this species can be characterized by the large eye (maximum diameter 0.10-0.14 mm), composed of a single ommatidium, and located about 1½ diameters from the anterior margin of the head, and the four toothed mandible. It is a moderately large (total length about 5 mm), dark reddish brown species, with transverse rugulae on the dorsum of the head. The head length ranges from 0.99 - 1.03 mm, the head width 0.74-0.82. The anterior margin of clypeus is moderately acute, but does not form a spine. The scape (0.96-1.06 mm) extends about 1/3 length past the posterior lateral corner of the head. The anterior border of the mesonotum is distinctly lower than the posterior edge of pronotum; the mesonotum to the anterior part of propodeum is concave. The anterior and posterior faces of the petiole are nearly parallel, and straight, and a well-developed, flattened, dorsal face is present. The spiracular horns (Figure 27) of the petiole are well developed. The subpetiolar process is rectangular shaped; the posterior face of the process is only slightly concave.

Erect hairs are sparse, and are present on the clypeus, mandibles, and gaster, the remaining hairs are suberect to decumbent, and present on the head, scape, dorsum of the mesosoma, petiole, and the legs, including the tibiae.

The mandibles are longitudinally striate, the dorsum of head has transverse rugulae, or striae, which curve anteriorly between the eyes and frontal carinae, and on the sides of head. The rugulae on the ventral surface of the head curve obliquely and extend anteriorly. The dorsum of the pronotum has transverse striae, which form concentric circles laterally, the mesonotum has transverse striae, the propodeum has transverse striae, which curve obliquely anteriorly and align with the striae present on the mesopleuron. The side of the petiole has a mixture of transverse (posteriorly) to obliquely vertical (anteriorly striae), the striae on the dorsum of the petiole are transverse, the postpetiole and the remainder of the gaster have fine, coriaceous sculpture, and are mostly smooth and glossy. The female and male are unknown.

Etymology
Named in honor of the collector, Bob Anderson, who has given us thousands of tropical ants.

References based on Global Ant Biodiversity Informatics

 * Longino J. T. L., and M. G. Branstetter. 2018. The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants. Ecography 41: 1-12.
 * Longino J. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/