Notes and Observations of Pogonomyrmex occidentalis (unfinished)

Pogonomyrmex occidentalis, or the Western Harvester Ant, is a species of harvester ant that, as the name suggests, inhabits a large part of the American coast in more arid habitats. It is the first species to have been approved for transport across state lines in the United States.


Taxonomy

Morphology

Pogonomyrmex occidentalis is a medium-sized ant.  It’s colours generally range in the brighter end on a spectrum of red. Workers are around 6-7 mm while queens are 8-9mm

The traits to distinguish Pogoomyrmex occidentalis are that they from other Pogonomyrmex

  • Have a lack of distinct hairs on the petiole
  • Have mandibles with 7+ teeth (Fig. 2.1)
  • Have a beaded “pattern” on the head, and the top surface of the petiole is rounded
  • The first mandibular tooth is turned upwards

Habitat

Pogonomyrmex occidentalis prefer rather arid habitats, though not completely arid areas, such as grasslands, sagebrush sites, and clearings in forests. They tend to thrive in areas with higher clay content. 

Range

Pogonomyrmex occidentalis are present in most of the Western United States and some of Canada. The northern part of their range extends to Medicine Hat, AB, Canada, and the Okanagan Valley Region in BC, Canada. They extend eastwards to around 98 degrees West and extend southward to the Chihuahua province of Mexico. The range of Pogonomyrmex occidentalis extends west to the California-Nevada border, tapering out around central California. Populations of Pogonomyrmex seem to be most abundant in the temperate grassland.

At the Nest

Pogonomyrmex occidentalis builds mounds that are anywhere from 5cm to 25cm high and from 30 cm to 135 cm wide. Surrounding this area is a clearing that reached 300 cm in diameter, with the average being around 150 cm. Workers of Pogonomyrmex will purposely clear out the vegetation around the area. There are many theories surrounding why this is, 

Nuptial Flights

Pogonomyrmex occidentalis generally have their flights throughout the month of July. Starting in late June in the Southern parts of their range, flights seem to progress linearly northward, ending in flights that occur just north of the Canadian border in late July.

Flights of this species are generally triggered solely by rain. Nests have been recorded to produce 180 alates on average, with around 50% more males than queens, and up to 1300 on rare occasion. After Summer rains, During the days leading up to nuptial flights, small numbers of Pogonomyrmex occidentalis alates can be observed around surveying areas near their home nests and poking out of their nests. Pogonomyrmex occidentalis nests release alates a single time, but will do so up to 3 times. On the flight day queens may be observed running around the nests in larger numbers. Flights begin at roughly 4pm, and alates are continuously released until around 5-6pm. Alates congregate on hilltop leks. Queens are visible in larger number for the first few hours after the flights and are progressively harder to collect after flights. Queens can be collected by digging up claustral chambers for around 3-5 days after the initial flights. Founding chambers will be marked by mounds of dirt with no ¾ circle pattern(Figure 3.3). After the first few days, chambers will frequently exceed a foot in depth. Pogonomyrmex occidentalis are facultative foragers, with some populations being predominantly foragers and some populations being predominantly fully claustral. Individuals that differ from this norm exist in each population, and foraging queens can be occasionally found from 1-2 weeks after the initial flights.

Founding Behaviour

Unlike many species of Pogonomyrmex, Pogonomyrmex occidentalis are facultatively semi-claustral, meaning that they can usually rear workers without extra food. However, feeding the queens are very strongly recommended to increase survival rates and increasing their worker numbers. Queens to do much better with a substrate or a natural material as well. Workers will generally appear after 3-4 weeks after founding at 30° C, but that time may double when reared at 25° C or lower[1]

Diet

Pogonomyrmex occidentalis need a source of both protein and carbohydrates. In the wild, Pogonomyrmex prefer seeds, insects, and nectar and can be fed on a similar diet to most other ants. Caution must be exercised to ensure that seeds are pesticide-free.

Nest Requirements

Pogonomyrmex occidentalis prefer 30-40% humidity and 30-38° C. Substrate is strongly recommended