Acromyrmex coronatus (Fabricius 1804)

Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia

worker face view

worker lateral view


Guatemala to Brazil and Ecuador.


Median pronotal spines usually present and distinct, occasionally reduced or absent; head tapering behind eyes; head width less than or equal to 1.7mm.

Natural History

Acromyrmex coronatus is a montane species found in cloud forest habitats and not in the lowlands. It is tolerant of cold, wet conditions and colonies can be found in small clearings and gaps in dense cloud forest. On the transect on the north side of Volcan Barva it has been found at 1100m elevation but not at 500m or 2000m. On the Central Valley side it has been collected at 1600m elevation at Zurqui. In the Monteverde area it occurs in the community area, up to the highest ridges at 1700m, and down to 800m in the Penas Blancas Valley.

In Monteverde, it is the main pest in gardens and will come into houses at night to cut bread, cabbage, or fruit that has been left out. The nests are often in or under a piece of dead wood, and often with a superstructure of loose dead leaf fragments. They do not excavate soil very extensively if at all. They may be arboreal at times, nesting in a low branch junctions of epiphyte-laden trees.

Lisa Ellis, an undergraduate student with the University of California Education Abroad Program in the late 1980's, carried out a study of A. coronatus foraging during the transition from dry to wet season in Monteverde. She found that foraging was continuous at night, but diurnal foraging only occurred when there had been recent rain. Following a heavy rain, diurnal foraging would commmence followed by a gradual cessation over a period of a day or two. Periodic rains during the dry season would initiate a short bout of diurnal foraging, but when the rains became more continuous diurnal foraging became continuous. Thus the lack of diurnal foraging during the dry season was a short-term response to immediate environmental conditions and not a long-term change in colony foraging behavior.

Nuptial flights are common in Monteverde and the distinctively-patterned dealate queens are often seen on the roads. On 9 July 1984 I observed a swarm of males in the canopy of an emergent oak on the ridge crest above Monteverde. Hundreds of males were swarming just above the highest branches of the tree. Later in the day I saw many dealate queens on the roads.

I have observed aggregations of founding queens under epiphyte mats in recent treefalls. Several times I have seen dealate queens out cutting leaves, suggesting that queens need to forage themselves to establish a colony.

Taxonomic notes

Formica coronata Fabricius 1804:413. Holotype (unique syntype) queen: South America [Copenhague museum, according to Santschi 1925].

Acromyrmex coronatus (Fabricius); Emery 1922:348.

Atta (Acromyrmex) moelleri v. panamensis Forel 1899:35. Syntypes: Guatemala, Sinanja en Vera Paz (Champion) [queen]; Costa Rica, La Palma (Alfaro) [workers?]; Panam‡, Volc‡n de Chiriqui, 4000-6000ft (Champion) [worker, queen].

Atta (Acromyrmex) moelleri st. panamensis var. angustata Forel 1908:41. Worker: Costa Rica, La Palma, 1000m, No. 23 (Biolley) [specimen data in Santschi 1925 not quite correct] [NHMB] (examined) (unavailable name).

Atta (Acromyrmex) moelleri subsp. rectispina Forel 1908:41. Syntype workers: Costa Rica, La Palma, 1600m, No. 24 (Biolley); Costa Rica (Tristan) [MHNG, NHMB] (NHMB specimens examined).

Acromyrmex coronatus st. importunus Santschi 1925:362. Syntype workers: Costa Rica, La Palma, 1600m, No. 77 (Biolley) [NHMB, MHNG] (NHMB specimens examined). The types look exactly like rectispina types, except median pronotal spines are absent.

The following is part of the key from Santschi's 1925 Acromyrmex revision:

42. Median pronotal spines developed and well-spaced, or posterior mesonotal spines greater than one half length of anterior mesonotal spines; inferior pronotal spines straight or curved posteriorly.....51
--. Median pronotal spines very short and closely spaced, often together on a common projection, or reduced to two tiny tubercles, or absent; posterior mesonotal spines less than one half length of anterior mesonotal spines; inferior pronotal spines usually directed forward........43

43. Tubercles on gaster more or less arranged in 4 longitudinal series; median pronotal spines absent or reduced to minute tubercles; inferior pronotal spines straight or slightly curved anteriorly; red or brown; maximum length 4.5mm..........importunus
--. Tubercles on gaster irregularly distributed, with a more or less narrow median smooth space; inferior pronotal spines distinctly curved anteriorly on major worker........(various non-Costa Rican taxa).

51. Dark brown; mandibles and spines reddish; length 2.5-4.5mm.......rectispinus
--. Red ochre, more or less ferrugineus............52

52. Median smooth space on gaster bordered by tubercles that are considerably larger and united in groups.......53
--. Tubercles bordering smooth space not noticably larger or more confluent than others; spines on occipital angles somewhat erect and usually straight; eyes very convex; length 3-5.5mm........coronatus (only SE Brazil in Santschi interpretation).

53. Median pronotal spines slender at the base; gaster uniformly reddish ferrugineus; maximum length 7mm..............panamensis
--. Median pronotal spines thick at base; gaster with two clear spots.....angustatus.

The characters used to differentiate panamensis, angustata, rectispina, and importunus I interpret as intraspecific variation. Biolley and Alfaro collections from the single site La Palma are part of the syntypes of panamensis and rectispina, and the sole syntypes of angustata and importunus. I have no evidence of sympatric species within the coronatus lineage in Costa Rica. panamensis is the regional name with priority, but the characters differentiating panamensis from coronatus s.s. are weak (relatively sharper tubercles in panamensis). All these taxa should be synonymized with coronatus until evidence to the contrary is produced.

Page author:

John T. Longino, The Evergreen State College, Olympia WA 98505

Date of this version: 22 October 2003.
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