Pogonomyrmex californicus


The California harvester ant exhibits specific behaviors to achieve high reproductive success. Male ants within the genus Pogonomyrmex assemble in large groups on the ground, on low shrubs, and around tall objects such as trees and chimneys, and they can remain sexually active for quite a few days (Mintzer 1982). Mintzer also noted that volatile secretions are released from the mandibular glands, causing females and other males to fly upward to the aggregation sites in his 1982 article. Most often, females copulate several times with different males, one after another, in June and early July when temperatures exceed 30 degrees Celsius - perfect conditions for mating flights to help increase colony size (Mintzer 1982).

Colonies of Pogonomyrmex californicus are founded without workers by at least one queen and grow to have thousands of workers at maturity, all of which are of one form (Holbrook et al. 2011). Though single queens found nests in most P. californicus populations, there is a localized population in San Diego County, California, that displays what is known as pleometrosis, which is the event of colony founding through multiple queens; it is the only known occurrence of this phenomenon (Johnson 2004). Pleometrosis allows the colony to speed through its early growth stages, increasing colony survival and enabling earlier production of sexual offspring (Johnson 2004).
P. californicus ant colony. Retrieved from Wikimedia Commons.
Primarily, multiple queen populations arise through haplometrosis, or colony founding by one queen, and when a California harvester ant colony is well-established, the secondary queens can enter the nest (Navajo Nature 2010). According to the same website, multiple queens do not exist indefinitely, however; during the late stages of a colony’s founding, the queens will fight each other to have control over the nest. P. californicus workers may also start to kill individual queens (Navajo Nature 2010). Either way, the consequence is that only one queen will receive complete control over egg-laying in the colony.

Multiple queens must gather resources to raise their offspring by exposing themselves to risks caused by foraging, just as single queens must in order to raise their first offspring; thus, they are known as obligate foragers (Navajo Nature 2010). Queens forage for only a short time before they revert back to large-scale egg production in the nest, and their ovaries’ functionality is kept during foraging (Dolezal et al. 2012). Workers, on the other hand, are no longer able to produce healthy eggs when they begin to forage, and their ovaries slowly begin to decay most probably because of reduced ovarian activity and ecdysteroid levels (Dolezal et al. 2012).

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