Halictus ligatus

For H. ligatus, similar to other eusocial halictids, the differences in reproductive strategies among females correlate with distinctions in body size and appearance.[8] For instance foundresses, or queens, tend to be large-bodied females in order to maximize energetic reserves, thereby enabling them to overwinter, establish nests, and reproduce independently.[8] On the contrary, helpers tend to be smaller-bodied daughters with undeveloped ovaries.[8]

H. ligatus typically nests in level, well-drained, hard-packed soil free of vegetation.[7] As a result, these nests are most frequently encountered in dense aggregations in dirt roads and paths.[7] The tendency for H. ligatus to nest in aggregations is advantageous for the cooperation of bees for the repulsion of parasites.[7] However, this behavior can also be disadvantageous as it minimizes the time spent by predators in search of prey, or parasites in search of hosts.[7]

In general, H. ligatus will continue to utilize a nest site year after year until it becomes too crowded as a result of encroaching vegetation or parasites and diseases.[7] The overwintered queens actually prefer to remodel old nests in order to initiate new nests.[7] Presumably, those bees which nest at old sites and in old nests tend to produce a greater number of descendants than those who nest elsewhere.[7] As a result, selection favors the continued use of this site.[7] However, in situations in which a sudden catastrophe has eliminated the original nesting site, the bees will of course be forced to select a new site.[7] This new site will be selected favoring those bees who have already dispersed, in an effort to select individuals who possess the tendency to disperse again in the future.[7]

The nests of H. ligatus occur either in rotting wood or within the ground.[11] They have diverse ways of setting up ground nests which can include small cells, scattered cells, and clusters of cells depending on the size of the colony. Nests inside rotting wood are usually irregular in shape due to the constraints of their medium. The area around the cells is usually uncovered and the cells are lined with a waxy substance from the Dufour's gland of the bee.[12] which is used to protect developing bees.

The vast range of distribution contributes to the variations in behavior and dominance hierarchy observed for individuals of the species living in different environments. For instance studies indicate that annual variation in local weather conditions actually directly influences the demography of these sweat bee colonies, thereby indirectly influencing the nature of social interactions among adult females.[11] In fact, habitats experiencing adverse conditions caused by excessive rainfall resulted in poor brood survival, production of fewer workers, and queen-dominated oviposition.[11] Under more favorable conditions such as warm weather, it was found that colony and brood survival was high, large numbers of workers were produced, and workers were responsible for a larger proportion of eggs laid in the reproductive brood.[11] These distinctions in environment may also affect colony size and decrease eusociality. For instance, in southern areas with long nesting seasons where there are a large number of workers per nest, queen control of worker behavior is less effective than in northern areas with shorter nesting seasons where there are fewer workers per nest.[11]

Female sweat bees of H. ligatus exhibit a wide range of reproductive roles, ranging from typically foundress (or queen-like) to typically worker-like.[14] Nests founded in the spring are mostly haplometrotic or founded by a single queen.[14] A few others, around 12%, are pleometrotic or founded by anywhere from 2 to 6 queens.[14] In these pleiometric associations, dominant foundresses behave in a manner similar to haplometrotic queens while subordinates behave like mid-summer workers.[14]

The choice of reproductive role available to a particular female is generally dictated by several important factors at the time of emergence including social milieu of the nest, body size and fat stores at eclosion, and time of year.[14] For instance, females that emerge in mid-summer that are small, have few or no fat stores, and whose nesting includes a larger queen tend to develop as workers who assist their mothers to raise the second, reproductive brood. On the contrary, females that emerge in late summer that are large and have large fat stores are destined to mate and become queens of their own nests in the following spring.[14]

Typical queens in single foundress colonies exhibit behaviors consisting of solitary nest excavation and spring provisioning for the brood followed by queen-type behavior after the mid-summer emergency of workers.[14] These behaviors include ceasing to forage and instead overlooking the workers of the colony.[14] For colonies in which there exist multiple foundress associations, subordinates continue to forage while their social role more closely resembles that of a mid-summer worker as opposed to a haplometrotic spring queen.[14]

H. ligatus worker individuals experience varying levels of eusocial behavior and colony organization depending on the environmental conditions. For instance, under harsher environmental conditions, there is more classical eusocial behavior. Therefore, the reproductive efforts of workers are generally focused on assisting the queen to raise the queen's reproductive offspring by tending to eggs, cleaning the facility, and foraging for food and water.[11] However, under gentler environmental conditions, there is a reduction in overall eusociality.[11] As a result, workers tend to focus more on raising their own reproductive offspring, including gynes.[11]

H. ligatus is a primitively eusocial species meaning that there is suppression of ovarian development in female workers by aggressive behavior of the queen. Aggression is most common in the queen of the nest, but it may be exhibited by other members, especially if the nest is larger.[15] The inhibition of ovarian development is accomplished by phermonal secretions and aggressive acts by the queen, who is trying to maintain herself as the sole egg layer. When there is a nest with multiple foundresses, one will assume the reproductive duties and become a guard while, the other a forager. This guard will protect the nest from intruders and assume a C- shape with the head and stinger directed toward an intruder to threaten them. Familiar members of the nest are allowed in based on familiarity, age, and smell [3] If a queen happens to die during the season when the nest is still highly active a replacement queen will be chosen from the workers, who will begin to exhibit the same types of behaviours as the previous queen.[16] When climate is harsh or breeding season becomes short, some members of the colony may become socially polymorphic and revert to a solitary lifestyle,[17] an adaptation to varying environmental conditions.

In the rare occurrence of nests which contain more than one foundress, one individual will become the "guard".[3] These guards are reproductively dominant individuals, while other individuals assume foraging duties.[3] Single foundress nests, however, are left unguarded during foraging trips. As a result, these nests may be prone to experience conflict over nest ownership due to the occurrence of usurpation attempts.[3] These conflicts range from brief feuds of 5 seconds or less to prolonged fights lasting anywhere from 10 to 26 minutes.[3] During these encounters, the guard blocks the nest entrance with its abdomen and engages in thrusts to eject the intruder.[3] In fact, this may even involve mandibular aggression, which often leads to the loss of legs and other vital body parts.[3]

Due to the correlation between female body size and role in the colony, it becomes evident that larval diet plays an integral part in caste differentiation and sociality for H. ligatus.[8] In fact, the mother bee is often seen limiting the amount of resources and nutritious intake she provides to her offspring so that they are forced to develop into small and lean females.[8] This deliberate behavior ensures that these daughters are suitable for their roles as helpers, as a result of their incapability to perform independent reproduction.[8] Furthermore, small-bodied females may be desirable as they are much easier to manipulate into a subordinate role with the use of dominance interactions and aggression.[8]

In established nests, workers may directly compete with the queen as well as each other for oviposition, and attempt to lay their own eggs[3] though many workers forgo their own reproduction and provision for others' offspring.[14] However, many other workers lay eggs, thereby raising their own offspring in addition to the queen's.[14] In fact, around half of H. ligatus workers are inseminated and actually capable of producing diploid eggs.[14]

H. ligatus are a generalist species when pollinating [21] and will pollinate a variety of different plants via their foragers. Much of the pollen collected will become part of the provisions in the nest, but many stigmas of plants are pollinated while foragers are collecting what they need.[21]

The amount of provisions that can be carried per foraging trip varies widely across different bee species. H. ligatus, for instance, participates in dry external pollen transport as opposed to internal transported or agglutinated external transport.[20] This type of pollen transport allows for more rapid pollen loading than the agglutination as it omits the step of nectar addition.[20]