Ectatomma ruidum

Prefers nesting in open areas, where this ant can occur in high density. These ants have a subset of foragers that specialise on food robbing, where individuals will enter other colonies' nests to steal their food.

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil, Colombia, Costa Rica, Ecuador, French Guiana, Guadeloupe, Guatemala, Guyana, Honduras, Martinique, Mexico, Nicaragua, Panama, Peru, Suriname, Trinidad and Tobago, Venezuela.

Biology
When alarmed, workers will feign death.

McGlynn et al. (2015) provided evidence to suggest thieves, stealing food from their non-natal nest, are a distinct caste of workers that specialize in this behavior. They also nicely summarize what is known about this behavior in this species.

In E. ruidum, intraspecific thievery among adjacent colonies is readily observed (Guénard and McGlynn, 2013). Ectatomma ruidum thieves specialize in stealing food from another colony (i.e. the ‘victim nest’); the cuticular hydrocarbon profile of thieves is intermediate between the colony to which they are bringing food and the colony from which they are removing food, presumably obfuscating nestmate recognition cues, and thieves are not known to switch to a nonthieving foraging habit (Breed et al., 1992; Jeral, Breed, and Hibbard, 1997). Thievery is thought to be evolutionarily stable only at low frequencies (Brockmann & Barnard, 1979; Ruxton and Broom, 1999), but thieving is a common activity in E. ruidum colonies, at least in Costa Rica and Panama (Breed, McGlynn, Stocker, and Klein,1999). Like other social insects, colonies of E. ruidum are less vigilant against interlopers when food is relatively abundant in the environment (Guénard and McGlynn, 2013).

Thievery in E. ruidum is uniquely overt and widespread, and is undetected in other ant species. Intraspecific kleptoparasitic behaviour in E. ruidum persists despite the fact that colonies are more vigilant against thieves when more thieving occurs (Jandt, Hunt, and McGlynn, 2015). It is broadly accepted that the ecological success of social insect colonies emerges from the collective ability to acquire resources and defend them from competitors. Thievery within E. ruidum suggests very poor abilities in protecting resources, but this species is nevertheless among the most widespread and locally abundant ants in the Neotropics (Schatz and Lachaud, 2008). To address this apparent contradiction, we wish to understand how foragers that act as thieves and collect resources from the insides of neighbouring nests are distinct from ‘normal’ (nonthief) foragers that collect resources from the surrounding leaf litter.

As regards the findings of their study of thieves as a distinctive type of worker, they found: Every colony of E. ruidum simultaneously maintains individuals that collect the same type of food item, but with two distinct foraging strategies. Workers of these foraging types are behaviourally distinct from one another but rely upon a common pool of food resources. The disparate behaviours that make up these two strategies effectively serve to repartition the original pool of resources gained during primary foraging. The first foraging strategy is ‘normal’, with workers that collect food from within their territories. These individuals find food within the home range, walk in a straight line back to the nest, encounter other ants along the way, interact with them, and carry on in a nonchalant fashion. The second foraging strategy is thievery, in which workers collect food from inside a colony that is outside their own colony's home range. These individuals walk more slowly, pause more frequently and avoid encountering conspecifics en route. These individuals are also more prone to reverse direction when perturbed and to drop their pilfered food items when grabbed.

Sociometry
Dominguez-Haydar et al. (2018) - Nest density was assessed in rehabilitated areas of “Cerrejón” coal mine (Colombia). We tested whether there is a relationship between spatial distribution pattern, age rehabilitation and temporal changes. Three sites with different ages of rehabilitation (1, 9 and 20 years) and a secondary forest were sampled during dry and rainy seasons. Within four plots (6 x 40m) per site, we located, counted and estimated the minimum distance among nests. Our results indicated that the number of active nests varied according to sites and sampling season, 166 nests ha-1 (forest) and 1333 nests ha-1 (9-y site). Our results indicated that the nest distribution strongly depended on the scale of observation. A uniform distribution pattern was also found, mainly at the local scale (plot level), while an aggregated and random distribution was found at the site level. We conclude that ant density responded mostly to seasonal changes (dry versus wet season).

Genetics
Meza-Lazaro et al. (2018) - We assembled mitogenomes from 21 ant workers assigned to four morphospecies (E. ruidum spp. 1-4) and putative hybrids of the Ectatomma ruidum complex (E. ruidum spp. 2x3), and to Ectatomma tuberculatum using NGS data. Mitogenomes from specimens of E. ruidum spp. 3, 4 and 2 x 3 had a high proportion of polymorphic sites. We investigated whether polymorphisms in mitogenomes are due to nuclear mt paralogues (numts) or due to the presence of more than one mitogenome within an individual (heteroplasmy). We did not find loss of function signals in polymorphic protein-coding genes, and observed strong evidence for purifying selection in two haplotype-phased genes, which indicate the presence of two functional mitochondria' genomes coexisting within individuals instead of numts. Heteroplasmy due to hybrid paternal leakage is not supported by phylogenetic analyses. Our results reveal the presence of a fast-evolving secondary mitochondrial lineage of uncertain origin in the E. ruidum complex.

Queens
Queen microgynes — an isometric reduction of the large morph — are only known from Mexico (Lachaud et al. 1999a, b). Microgyny in this species is related to polygyny and dependent colony founding (Lachaud et al. 1999a, b; Lenoir et al. 2011). Young mated microgynes are readopted by a conspecific colony, most often their natal nest, and can contribute to colony growth by egg laying. These small queens represent one of two independently derived queen reductions in the genus (Nettel-Hernanz et al. 2015).

Nomenclature

 *  ruidum. Ponera (Ectatomma) ruida Roger, 1860: 306 (w.q.) BRAZIL. Borgmeier, 1934: 95 (m.); Wheeler, G.C. & Wheeler, J. 1952a: 131 (l.). Combination in Ectatomma: Mayr, 1862: 732. Senior synonym of scabrosa: Roger, 1862c: 292; of aztecum: Kugler, C. & Brown, 1982: 2.
 * scabrosa. Ectatomma scabrosa Smith, F. 1862b: 31 (w.) PANAMA. Junior synonym of ruidum: Roger, 1862c: 292.
 * aztecum. Ectatomma aztecum Emery, 1901a: 50 (w.) MEXICO. Junior synonym of ruidum: Kugler, C. & Brown, 1982: 2. See also: Brown, 1958g: 295.

Ectatomma scabrosa

Three worker syntypes in. The syntypes are flat-mounted, each on a roughly hexagonal piece of card. Along the basal border, behind the pin, is “Panama,” and on the reverse of the card the number “13.”