Abstract
The collective behavior of ant colonies, and locomotion of individuals within a colony, both respond to changing conditions. The invasive Argentine ant (Linepithema humile) thrives in Mediterranean climates with hot, dry summers and colder, wet winters. However, its foraging behavior and locomotion has rarely been studied in the winter. We examined how the foraging behavior of three distinct L. humile colonies was related to environmental conditions and the locomotion of workers during winter in northern California. We found that colonies foraged most between 10 and 15°C, regardless of the maximum daily temperature. Worker walking speed was positively associated with temperature (range 6–24°C) and negatively associated with humidity (range 25–93%RH). All colonies foraged during all day and night hours in a predictable daily cycle, with a correlation between the rate of incoming and outgoing foragers. Foraging activity was unrelated to the activity of a competing native ant species, Prenolepis imparis, which was present in low abundance, and ceased only during heavy rain when ants left foraging trails and aggregated in small sheltered areas on trees.
Highlights
The invasive Argentine ant, Linepithema humile, is established in Mediterranean climates worldwide, where it is unicolonial and seasonally polydomous
All three L. humile winter aggregations maintained consistent bidirectional foraging trails on Quercus agrifolia (Coast live oak) trees, with maximum sustained foraging rates ranging from 0.29–0.95 ants s-1 and forager walking speeds from 1.85–2.46 cm s-1
We found that L. humile colonies foraged from winter aggregations during all day and night hours
Summary
The invasive Argentine ant, Linepithema humile, is established in Mediterranean climates worldwide, where it is unicolonial and seasonally polydomous. Workers, queens, and brood are distributed among multiple nests linked by a trail network that expands and contracts seasonally. During the polydomous summer phase, many workers can quickly recruit to nutritional resources directly from the colony’s vast trail network [1], and use the network to distribute resources among multiple nests [2]. Colonies condense during winter in Mediterranean climates, to aggregate in a single nest with very few foraging trails [3,4,5]. Winter conditions, including precipitation, cool temperatures, and decreased sunlight, reduce resource availability relative to summer conditions [6, 7].
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