The variation in animal mating systems has received a great deal of attention from behaviorists and evolutionary biologists alike (Shuster & Wade 2003). Polyandry, the mating of a single female with multiple males, is evolutionarily derived (Hughes et al. 2008) and relatively rare in social insects (Strassmann 2001). Modest polyandry has evolved in Vespula wasps (Ross 1986; Foster & Ratnieks 20...

Structures influence how individuals interact and, therefore, shape the collective behaviours that emerge from these interactions. Here I show that the structure of a nest influences the collective behaviour of harvester ant colonies. Using network analysis, I quantify nest architecture and find that as chamber connectivity and redundancy of connections among chambers increase, so does a colony...

We examined the scale of recruitment limitation in the western harvester ant, Pogonomyrmex occidentalis (Cresson). We measured colony density of 98 plots (0.25 ha) over an area of 500 ha. By applying an interpolation/extrapolation analysis to the spatial variability in colony density, we were able to accurately identify the location of two mating swarms. These two swarms were 1,400 m apart. Con...

We investigated how foragers are activated in colonies of the red harvester ant, Pogonomyrmex barbatus. Each day, a harvester ant forager makes many trips out of the nest to gather seeds and bring them back to the nest. The rate at which foragers return to the nest is linked to food availability: when food is easy to find, foragers return more quickly. We examined how the return of successful a...

Harvester ant colonies adjust their foraging activity to day-to-day changes in food availability and hour-to-hour changes in environmental conditions. This collective behavior is regulated through interactions, in the form of brief antennal contacts, between outgoing foragers and returning foragers with food. Here we consider how an ant, waiting in the entrance chamber just inside the nest entr...

Adult worker of Pogonomyrmex sp. Photo courtesty of J.O. Schmidt Insects in the order Hymenoptera were recorded as early as the 26th century BC as possessing a venom toxic to vertebrates. Harvester ants in the genus Pogonomyrmex have the most toxic venom based on mice LD50 values, with P. maricopa venom being the most toxic. The LD50 value for this species is 0.12 mg/kg injected intravenously i...

Local interactions, when individuals meet, can regulate collective behaviour. In a system without any central control, the rate of interaction may depend simply on how the individuals move around. But interactions could in turn influence movement; individuals might seek out interactions, or their movement in response to interaction could influence further interaction rates. We develop a general...

-The Dufour gland secretions of Messor minor, Messor capitatus and Messor bouvieri differ from those of other myrmicine ants so far studied in having no sesquiterpenoids present. M. minor resembles the North American harvester ants, Pogonomyrmex, in containing branched chain hydrocarbons. Messor and Pogonomyrmex appear anomalous among myrmicines and more closely resemble some formicines in this...

In the seed-eating ant Pogonomyrmex barbatus, the return of successful foragers stimulates inactive foragers to leave the nest. The rate at which successful foragers return to the nest depends on food availability; the more food available, the more quickly foragers will find it and bring it back. Field experiments examined how quickly a colony can adjust to a decline in the rate of forager retu...

Social groups balance flexibility and robustness in their collective response to environmental changes using feedback between behavioural processes that operate at different timescales. Here we examine how behavioural processes operating at two timescales regulate the foraging activity of colonies of the harvester ant, Pogonomyrmex barbatus, allowing them to balance their response to food avail...