Diet and Spatial Pattern of Foraging in Ectatomma opaciventre ...

607 

Diet and Spatial Pattern of Foraging in Ectatomma opaciventre 

(Hymenoptera: Formicidae) in an Anthropic Area 

by 

Viviane Cristina Tofolo 1,2 , Edilberto Giannotti 1,3 , Hugo Ribeiro Moleiro 1 

& Marcos Rogério Simões 1 

ABSTRACT 

Ectatomma opaciventre (Formicidae: Ectatomminae) presents an individual 

foraging strategy in the epigeal stratum. It is a generalist predator, collecting 

a wide variety of live or recently dead arthropods. The objective of this study 

was to determine individual foraging pathways and identify prey types in 

the diet of this species. The individual foraging pathways of 3 colonies were 

determined by following foragers in the field and recording the time and maximum 

foraging distance from the nest. Diet was assessed by the collection and 

identification of the prey carried between the mandibles of the ants. Foragers 

collected mainly other species of ants. The maximum foraging distance was 

5.14 m and the longest time spent foraging was 66 minutes. The pathways 

appeared to be spatially distributed in a way that avoids intersection with 

pathways from other nests and favors search for food in areas unexplored by 

other individuals. 

INTRODUCTION 

The trail system of ant colonies offers a mechanism that determines the 

patterns of search for food by foragers, directing them away from neighboring 

colonies (Hölldobler 1976; Harrison & Gentry 1981; Ryti & Case 1986; 

Traniello 1988). It also reduces search time, leading foragers to a persistent 

resource (Hölldobler 1976; Shepherd 1982, 1985). The food search pattern 

may consist of the use of a foraging area by populations, so that intra- and 

interspecific territorial interactions contribute to the partitioning of the environment 

between colonies. Furthermore, each search started by a forager 

may have a particular spatial and temporal organization, which is ecologically 

1 Universidade Estadual Paulista [São Paulo State University] Júlio de Mesquita Filho, Zoology 

Department - Av. 24-A, 1515 - Bela Vista - CEP: 13506-900 - Rio Claro, SP, Brazil. 

2 E-mail: vivitofolo@yahoo.com.br 

3 E-mail: edilgian@rc.unesp.br

608 Sociobiology Vol. 58, No. 3, 2011 

influenced. There is also a relation between individual and collective search 

patterns, since the forager may influence the search patterns of a nestmate 

through communication. Therefore, the distribution of resources in space 

and time should be the main influences upon the organization of search 

(Traniello 1989). 

There is a tendency for ant species with small colonies to forage individually 

and not to present complex recruitment systems, because individuals interact 

directly with few foragers. On the other hand, colonies with a lot of individuals 

rely on long-term chemical communication between the individuals, allowing 

for rapid recruitment of numerous foragers. Between these extremes, there 

are intermediate behaviors such as tandem running, group recruitment, and 

mass recruitment (Beckers et al. 1989). In Ectatomminae, foragers may use 

a wide variety of strategies to obtain food. The foraging methods may vary 

from hunting independently, with no cooperation during food search and 

collection, to various degrees of cooperation, with different levels of communication 

and recruitment between nestmates. However, a wide range of 

feeding habits can be observed from species to species, including the collection 

of seeds, fruits, living prey, and insect secretions (Hölldobler & Wilson 

1990; Medeiros & Oliveira 2009). 

Among the ants of the genus Ectatomma, endemic to South and Central 

America (Brown-Jr 1958; Bolton 1995), several foraging strategies may occur, 

such as ambush predation, solitary hunting, cooperative and group hunting, 

and even cleptobiosis (Perfecto & Vander Meer 1993; Schatz & Wcislo 1999). 

As their colonies are small, foraging is more often solitary (Hölldobler & 

Wilson 1990). With a large, functional sting and well-developed mandibles, 

they are capable of subjugating large, aggressive prey, a characteristic typical 

of essentially predator species (Hölldobler & Wilson 1990; Wheeler 1986; 

Giannotti & Machado 1992; Fernández 1991; Oliveira & Brandão 1991; 

Del-Claro & Oliveira 1999; Pie 2004). Regarded as a generalist predator, 

Ectatomma opaciventre uses the hypogeal stratum for nesting and the epigeal 

for foraging a wide variety of arthropods and annelids, living or recently dead 

(Fernández 1991; Pie 2004). 

The objective of this research was to determine individual foraging pathways 

of workers of E. opaciventre and identify prey types in the diet of this 

species in an anthropic area.

Tofolo, V.C. et al. — Spatial Pattern of Foraging in E. opaciventre 

MATERIAL AND METHODS 

Three nests of E. opaciventre were found in an urban area of 4,800 m 2 in 

the city of Rio Claro, SP, Brazil (22º 22'42.31"S and 47º 33'38.67"W). This 

grass-covered area was frequently used for garbage disposal and often set on 

fire. The foraging pathways were determined based on the focal-animal sampling 

method. Foragers were individually observed from the moment they left 

the nest until they returned. As the ant moved, a numbered tag was placed 

on the ground every 20 cm (Fig. 1). In cases where ants appeared disturbed 

by the observer, the data were discarded. The duration of the foraging trip 

and maximum foraging distance was recorded for 10 individuals per nest, 

for a total of 30 observations. An analysis of variance with a 95%-confidence 

interval was carried out in order to verify whether there were differences in 

the foraging distance and time between the 3 nests studied. Then, BioEstat 

software, version 3.0, was used to calculate the Spearman’s correlation coefficient 

between the time and distance of foraging. 

To evaluate the diet of the ants, we recorded the number of workers leaving 

and entering the nest and we collected, with tweezers, the items that they 

Fig. 1. Representation of the numbered tags placed every 20 cm to follow movement by the foragers 

of Ectatomma opaciventre. 

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carried to the nest in their mandibles. The observations were made in the dry 

season from 14:00 to 18:00, which corresponds to the period of the highest 

foraging activity for this species in the afternoon (Pie 2004). The total time 

of observation was 72 hours. The food collected was stored in 70% alcohol 

for further identification. 

RESULTS 

Foraging pathways 

The workers of E. opaciventre foraged on average at a maximum distance of 

2.18m ± 1.6m (SD) (range: 0.40-5.14 m), spending on average 28.1 ± 15.6 

min (SD) (range: 8- 66) outside their nest. The maximum foraging distance 

from the nest and the trip duration are presented in Table 1. Workers of nests 

1, 2, and 3 showed no significant difference in the distance or time of foraging 

(p> 0.05). The Spearman’s rank correlation coefficient for the variables 

time and distance was r = 0.848 (p


The foraging trails presented a sinuous pattern from the beginning to the end, 

with directional fidelity (Fig. 2). The pathways from nest 1 were concentrated 

around the nest along the north-south axis; in nest 2, they were distributed 

southeast and northwest to the nest; and in nest 3, they were west-oriented. 

Thus, the foragers were spatially distributed in the foraging area so as to avoid 

overlap with the trails from neighboring colonies. These areas were explored 

repeatedly, demonstrating the preference of colonies for specific regions in 

the foraging arena. In the 3 colonies, most trajectories were close to the nest, 

with few pathways more than two meters away from it. 

Diet and foraging effort 

During the observation period, few foragers left the nest in search of food 

resources. The workers of E. opaciventre left the nest on average 5.4 ± 2.7 (SD) 

times per foraging hour, returning almost at the same rate, 4.9 ± 2.5 (SD) 

times. Of the 371 foraging trips recorded, only 9.16% ended with the workers 

returning with prey. Liquid food was not observed in the mandibles of the 

foragers, only solids. The description of the prey captured is shown in Table 

2. Over half of the prey items collected (52.78%) belonged to Formicidae, 

including an individual of the same genus, E. brunneum. All the prey were 

collected individually except a chrysalis of Lepidoptera for which there was a 

recruitment strategy known as social facilitation. In this event, an individual 

recruited a nestmate to collect the prey item without using a scent trail. As 

the prey was too large and fixed to the substrate by silk threads, the forager 

quickly returned to the nest and then left, followed by another ant. The 

recruited ant followed the recruiter to the food source and both cut the silk 

threads to collect and transport the food item to the nest. 

DISCUSSION 

The diet of E. opaciventre was narrow, probably because the nests were 

located in a degraded area and the research was carried out in the dry season. 

In the Brazilian savannah (Cerrado), Pie (2004) observed that, in 50% of the 

cases, the diet of E. opaciventre is composed of termites, and over 20% of the 

other prey consists of other ants, mainly those of the genus Atta. 

Wheeler (1986) analyzed the diet of E. tuberculatum in Panama, also using 

the method of collecting prey items that workers carried to the nest. Insects 

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Fig. 2. Spatial pattern of foraging in three colonies of Ectatomma opaciventre 

in a degraded area in Rio Claro, SP, Brazil


Table 2 . Items collected by foragers of Ectatomma opaciventre in the 

field. The numbers in parentheses represent the relative abundance (%) 

of the items in each group. 

Prey Amount (%) 

Hymenoptera (55.56%) 

Ichneumonidae 1 (2.78) 

Formicidae (52.78%) 

(Ectatomminae) Ectatomma brunneum 1 (2.78) 

(Formicinae) Camponotus rufipes 3 (8.33) 

(Dolichoderinae) Conomyrma 5 (13.89) 

(Myrmicinae) Pseudomyrmex 5 (13.89) 

(Myrmicinae) Pheidole 5 (13.89) 

Lepidoptera (5.56%) 

Pyralidae 1 (2.78) 

Unidentified chrysalis 1 (2.78) 

Coleoptera (13.89%) 

Mycetophagidae 2 (5.56) 

Curculionidae 2 (5.56) 

Unidentified 1 (2.78) 

Araneae (2.78%) 

Salticidae 1 (2.78) 

Fragments (13.89%) 

Orthoptera 1 (2.78) 

Coleoptera 2 (5.56) 

Formicidae 2 (5.56) 

Grass seeds (8.33%) 3 (8.33) 

and other invertebrates, living or dead, were collected. Some of them were 

large and highly aggressive. Ants, especially Gnamptogenys, Odontomachus, 

Pheidole, Azteca, and Camponotus, were an important part of this diet (Pie 

2004; Pratt 1989). The same pattern was reported in a study by Giannotti and 

Machado (1992). They recorded 20 types of food of animal origin (insects 

and invertebrates) and several others of vegetal origin (like seeds, pulp, leaves, 

613


and roots) in the diet of E. brunneum (=quadridens). A preference for ants 

was also observed in E. permagnum, which showed a diet consisting almost 

exclusively of workers and winged individuals of Pheidole and Camponotus 

(Paiva & Brandão 1989), and in Pachycondyla striata, which includes in its 

diet foragers of Odontomachus, Camponotus, Pheidole, Solenopsis, Atta, and 

even other Pachycondyla (Medeiros & Oliveira 2009). 

The proportion of ants preyed on by E. ruidum was observed to be similar 

both in the dry (18.8%) and in the rainy (17.2%) season. Although its diet 

consisted of 19 items, almost 30% of them corresponded to liquids rich in 

carbohydrates, such as extrafloral nectar, honeydew, and fruit pulp (Lachaud 

1990). Similarly, in E. tuberculatum, liquid foods represented more than 35% 

of its diet (Valenzuela-González et al. 1995). Collecting resources of animal 

origin requires longer foraging distances; capturing and transporting them 

is more time consuming compared with liquid foods (Harkness & Harkness 

1976; Fourcassié & Oliveira 2002). This “preference” for other ants is not 

likely to be due to selectivity by the foragers, but to the low diversity of food 

items available in the environment. This can be proved in the laboratory, since 

workers of E. opaciventre easily accept other food items, such as mealworms, 

which are not found in their natural environment. 

The predatory behavior observed in E. opaciventre was very similar to that 

found by Pie (2004) in the Brazilian savanna and by Tofolo and Giannotti 

(2009) in the laboratory: prey aggressiveness determined the type of approach 

used by the workers. As a consequence of the absence of recruitment previously 

described for this species, the size of the food item collected was dependent 

on the capacity of the worker to carry it without help, one at a time. This 

behavior is characterized as social facilitation, that is, the return of a forager 

to the nest that may increase activity inside the nest, leading other collectors 

to leave and search for food sources even in the absence of a chemical trail or 

any other directional information, as observed in Pachycondyla goeldii (Orivel 

2000) and E. ruidum (Lachaud 1985). 

In the degraded area studied, the foragers of E. opaciventre did not stay 

more than 5.14 m away from the nest. A similar behavior was observed by 

Medeiros and Oliveira (2009) in numerous colonies of Pachycondyla striata. 

Fourcassié and Oliveira (2002) reported that, in Dinoponera quadriceps, 

this distance was more than twice as long, reaching 13 m. Pie (2004) also


recorded site fidelity in the area explored by workers of E. opaciventre, that is, 

the forager tended to have a preference for a specific foraging pathway, which 

made it a specialist in the individual exploration of sub-areas, becoming able 

to return to the nest quickly. The same pattern was observed in Pachycondyla 

apicalis (Fresneau 1985; Deneubourg et al. 1987), D. quadriceps (Azevedo 

2009), D. gigantea (Fourcassié & Oliveira 2002), Cataglyphis exhibits, and 

C. bicolor (Buchkremer & Reinold 2008). 

Fresneau (1985) proposed a simple mechanism to explain such fidelity: 

during the first trip, new foragers select a portion of the foraging area, which is 

confirmed by the capture of the first prey. Through a simple learning process, 

the ants keep searching in the same area during the following trips. If foragers 

from the same colony meet in an overlapping area, both make intense antennal 

contact before leaving for different pathways. This mechanism induces the 

forager to decrease search for food in areas used by other foragers, increasing 

the effectiveness of foraging on a colony-basis. Gordon (1995) believes that 

following the same direction enables foragers to explore a specific fan-shaped 

area, so as to deplete the resources in one direction before moving to the adjacent 

area. This way, when they return to the initial position, the resources 

are available again. This was also observed in P. striata (Medeiros & Oliveira 

2009), in the desert ant Veromessor pergandei (Rissing & Wheeler 1976), and 

in the army ant Eciton burchelii (Franks & Fletcher 1983). 

Seemingly, the individual foraging pathways of E. opaciventre are spatially 

oriented so as to avoid overlap with those from other nests, thus minimizing 

competition with individuals of other species. Considering that collectors 

do not use chemical markers on their foraging trails, researchers believe that 

landmark cues contributed primarily to the orientation of these ants in the 

field, as observed in D. quadriceps (Azevedo 2009), D. gigantea (Fourcassié 

et al. 1999), and Paraponera clavata (Deneubourg et al. 1987, Baader 1996). 

There are no studies proving magnetic orientation in E. opaciventre. 

Dinoponera quadriceps also presented a positive correlation between 

maximum distance to the nest and duration of foraging trip, with a sinuous 

movement pattern and directional preference (Azevedo 2009). According to 

Bonser et al. (1998), the time spent in the foraging area depends on the nest 

distance, and further areas must be explored less frequently and for longer 

615


periods than closer areas. This would explain the higher number of individual 

foraging pathways of E. opaciventre closer to the nest. 

Therefore, foraging strategies seem to depend upon several ecological 

variables, such as the distribution of food resources in time and space, food 

size and quality, competition, and predation. A colony must then have a spatial 

pattern of foraging to collect food effectively and minimize the chance 

of competition, in order to assure less energy waste and a greater input of 

resources in the shortest time. 

CONCLUSION 

The diversity of prey collected by E. opaciventre in the area studied was 

low, most probably because of the poor variety of species in the degraded 

environment and because the observations were carried out in the dry season. 

Collecting other ant species as the major part of its diet was likely due to the 

abundance and high richness of individuals belonging to several subfamilies of 

Formicidae in the area studied. The foraging trails of E. opaciventre presented 

a pattern similar to those observed in other Ectatomminae studied. With a 

sinuous profile and directional fidelity, these trails avoid competition with 

other nests and lead to a better division of the resources explored. Although 

most trips were unsuccessful, the foragers did not stray too far from the nest, 

nor did they spend too much time foraging. Since the area was dominated by 

grass, intense sunlight and heat was present, which could have caused the ants 

physical exhaustion if they had extended the time spent outside the nest. 

ACKNOWLEDGMENTS 

We thank the National Council for Scientific and Technological Development 

(CNPq) for the financial support. 

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