Myrmecocystus mexicanus

Only two castes in the colony reproduce, the queens and the males. Workers are sterile and tend to the queen and brood. Mating occurs during nuptial flights, where winged queens and males swarm outside the nest.[1]

The reproductives (winged virgin queens and males) start emerging from their native nest several days prior to nuptial flights, but are encouraged back into the nest by workers. Some reproductives die prior to flying off after not returning to their nest. Hours before the nuptial flight, queens, males and workers emerge from the nest and swarm around the entrance hole. Workers will then even nip at queens on the ground to encourage them to take flight.[5]

To mate, M. mexicanus winged queens and males emerge from an existing colony and swarm in nuptial flights. These flights occur in late July in the evening, typically at about the same time of day when the colony workers begin foraging. The flights usually occur the day after a rain. A normal nuptial flight lasts about an hour and half. After the flight, unmated queens and males return to the nest. The fact that some queens and males return from these flights unmated suggests that aerial union is difficult. The mated queens lose their wings, and the mated males die.[6]

After mating, a queen digs a nest chamber. About two days after her flight, she seals the nest chamber.[1] Conway found that many mated queens after digging and sealing nest chambers did not reappear later on, which could indicate a high mortality rate among newly mated queens.[7] Around five days after the flight, the queen lays eggs in clusters of 5–10. The larvae hatch around 20 days, and begin pupating in cocoons around 10 days after that. Adult workers emerge around 63 days after eggs are laid. Larvae are fed and cared for by the queen and workers. It is believed that the larvae may even be fed eggs and dead workers.[8] The workers in the first brood tend to be smaller than workers in subsequent broods, which is believed to be an adaptation to promote rapid population growth. The average worker lives from 11 to 170 days.[9]

The name honeypot ant comes from the peculiar development of replete workers, whose abdomens become so swollen with food that they are used by the rest of the colony as living food storage. They are "drained" during famine, usually the wintertime, to sustain the colony.[12] This behavior is an example of the caste system within ants and other eusocial insects. Repletes are a subset of the sterile "helper" caste.[3]

In M. mexicanus, replete workers develop from the largest workers in the colony. In fact, if the repletes are removed from a colony, the next largest workers quickly become repletes.[13] Typical workers and callows can develop into repletes in about two weeks. Other workers feed the developing repletes with plant nectar collected in the evenings. The repletes become so swollen that they become immobile, and hang from the ceilings of dome chambers in the underground nest.[14]

When a replete worker fills with food, her crop, or portion of her digestive tract, swells and displaces other abdominal organs.[12] The crop of replete workers expands about four to five times its normal linear dimension when they are fully engorged with food."[15] In M. mexicanus, the size of a replete worker’s abdomen ranges from 6–12 mm in length.[16] As repletes are drained of their food stores, they become "flaccid depletes".[14]

M. mexicanus repletes also vary in the content of their "honey" or food they carry. They can be classified according to the colors of their distended abdomens: dark amber, amber, milky and clear. Each color is thought to correspond with a particular food source. Dark amber and amber repletes contain sugars such as glucose and fructose, mostly likely from the nectar of flowers. Milky repletes contain large amounts of protein and oils, believed to be from insect prey. Clear repletes contain mostly water and sucrose (sugar), so they are thought to act as water storage for the arid climate.[17] Burgett & Young (1974) found that a small percentage of repletes had two visible layers of liquid in their crops– one consisting of sugars, and the other of lipids, glycerol and cholesterol esters.[18]

M. mexicanus collects food mainly in the form of nectar from yucca plants (Yucca glauca) and sugary galls formed on scrub oaks (Quercus gambelii). The gall wasp (Holcaspis perniciosus) forms the galls (rotund growths) along scrub oak branches, and these galls leak a clear sugary liquid on which the ants feed. Additionally, these ants feed on a variety of flower nectars, cacti fruit, and the excretions of aphids feeding on yucca plants. Workers will also collect dead insects and attack small, soft bodied insects.[19] In particular, M. mexicanus tends to feed on dead and moribund harvester ants (Pogonomyrmex occidentalis).[20]

As workers forage, their abdomens become clear and distended, similar to replete workers. When they return to the nest, they regurgitate their collected nectar into replete workers for storage. March through November is the typical foraging time for M. mexicanus. The summer months are when most nectar is collected. The ants forage in cooler temperatures ranging from 0.5 to 30 °C (32.9 to 86.0 °F) and mainly during the night. The lower temperature preference is most likely an adaptation to allow for nocturnal foraging in desert climates.[19]

Workers forage up to 20 meters (66 feet) away from the entrance of their nest. They exhibit both radial and path foraging patterns. Radial foraging (when the ants spread out radially from the nest entrance) happens mainly early in the season, when the ants are searching for nectar sources. Path foraging (when the ants follow frequently traveled paths) occurs later in the season once paths to nectar sources have been established.[19]

Other species of ants such as Conomyrma bicolor has been known to drop stones around the entrances of M. mexicanus nests. This behavior usually happens if the two species have colony entrances within 3 meters of each other. The two species have similar foraging times and food sources which creates competition between the colonies. The foraging of a M. mexicanus colony can decrease drastically due to this stone dropping technique.[21]