The California Harvester Ant

California Harvester AntThe California harvester ant or Pogonomyrmex californicus is a species of ant in the subfamily Myrmicinae found in Sn Bernardino County and which proliferates in the Mojave Desert. This ant is native to North America, where it occurs in the southwestern United States and northern Mexico. As the ant that is sent out in Uncle Milton’s Ant Farm, it may have established colonies in North America and elsewhere that are outside of its native habitat. The natural range of this ant extends from Texas to Utah, Arizona, Californai to Baja California, Sonora, and Chihuahua.
The California harvester ant is typically found in warm and open sandy areas. Either individually or in swarms or columns it will forage by day, preying upon arthropods and dead insects and collecting seeds and vegetation.
Pogonomyrmex californicus is a rapidly moving forager, which makes extensive use of thermal refuges such as small sticks or stones that allow it to enter a cooler layer of air and shed heat. Their average foraging distance is from ten to 18 feet from the nest. They concentrate their foraging in a single spot to optimize their activity and limit the time they spend in this activity and maximize energy returns. They are attentive to trying to collect the most profitable seeds, in terms of seed size.
The ants “harvest” the plants in their nesting areas by snipping off the seeds with their mandibles. These seeds are stored in subterranean or mound chambers within the nest, a warehouse of sustenance for the society through the winter.
Its colonies encompass hundreds or up to a few thousand of individual ants. They nest in sandy soil surrounded by a loose earth arranged in a circular or semi-circular pattern, generally in areas fully exposed to the sun. The entrances to those nests are often irregularly shaped. Some are beneath stones, whereas others are surmounted by soil craters or by small to huge mounds with or without coverings of gravel. In addition, the workers of some species alter the area peripheral to the nests by clearing away the plants, felling them, bit by bit, with their powerful mandibles.
Territories are well defined in populations where nests density is high. Interactions can occur between neighboring colonies, resulting in colony relocations. Nests may be overdispersed because a colony will resolve to move its nest further away from the nest of a neighbor.
As with most ants, the pogonomyrmex californicus abides in colonies sustained by one queen, but on occasion the California harvester ant has been known to form multiple-queen colonies in which the population remains in obeisance to more than one queen in a cooperative, a phenomenon known as pleometrosis. The multiple queen population of this species is striking in a exhibiting a number of unusual characteristics. First, most ant species that contain multiple queens arrive at this route through colony founding by a single queen, known as haplometrosis. It is only after a colony is well established that secondary queens are allowed to enter the nest. Adding additional queens is called queen adoption
Once a colony reaches a late stage in its founding process, the multiple queens that are part of a pleometrotic founded colony typically do not persist. The queens will fight among themselves for control of the nest, or the workers will begin to kill individual queens, or both of these behaviors occur. The result is a single queen gaining exclusive control over egg laying within the colony.
Reproduction occurs around July, when reproducing individuals are present.
Harvester ants are hot climate specialists. They are present almost everywhere in the Mojave National Preserve with the exception of blackbrush scrub between 1,000 and 5,700 feet. They are present in every month of the year and their populations have been surveyed in depth at or near Budweiser Spring, Granite Pass, Kelbaker Road, 1.5 miles east of Baker, Kelso Dunes, Rock Spring.
In most Pogonomyrmex californicus nests, the population consists primarily – well in excess of 95 percent – of workers. The California harvester ant is of smaller than average stature and sports coarse cephalic and thoracic rugae, the interspaces of which are strongly shining and faintly or not at all punctate. The petiolar node is short and rather broad, and it has a prominent nipple and a steep anterior declivity. The body is a concolorous, rather light, ferrugineous red. The sides of the propodeum are smooth and shining and there are no propodeal spines, teeth or denticles present. The California harvester’s rate of respiration gives it the ability to withstand relatively high temberatures, extending to as high as 124 degree Fahrenheit. This high heat tolerance of Pogonomyrmex californicus is coupled with a relatively small body size relative to most other Pogonomyrmex species. Being small assists workers in releasing heat more rapidly. This temperature tolerance is of significance since the ground where these ants forage can be well above 108 degree Fahrenheit during daytime.
With eastward progression in the range of harvester ant, the number of workers within individual nests decrease in number, spacing, and coarseness of cephalic rugae; often take on interrugal punctures on the head and pronotal humeri; show a decrease in gradient of the anterior declivity of the petiolar node; and evince the development of a more spatulate petiolar node, the sides becoming more convex. Further eastward migration of this ant has resulted in a reduction of the petiolar nipple and a tendency toward the development of a ventral petiolar peduncular process, the lengthening of both petiolar and postpetiolar nodes, a reduction in size of the postpetiolar ventral process; an increase in over-all size; and infuscation of the gaster in some or all of a series, from lateral spotting to concolorous black or brown.

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