Polybia sericea

P. sericea is a species within the genus Polybia of the subfamily Polistinae.^[6] Polybia is the most diversified genus within tribe Epiponini,^[2] which is characterized by colony founding via swarming. Placement of Polybia among related genera has fluctuated, and the genus may be paraphyletic.^[6]

P. sericea individuals are medium-sized wasps,^[4] about 17 mm long.^[1] They are dark in color, and tend to be slow-flying and docile, unless they are disturbed.^[4] Queens typically have larger abdomens, and smaller heads and wings than workers.^[2]

Workers build enclosed, multitiered, roughly spherical nests of carton paper maché-like pulp of plant fibres chewed with saliva.^[1] Nests are reddish-brown in color, and are not very large.^[2] They are typically built between 2 and 5 m off the ground,^[7] in the branches of trees or shrubs.^[1]

Individuals of P. sericea live in South America, and are commonly found throughout Brazil. A large population inhabits the lower tropical Amazon region of Brazil. They tend to live in semiarid climates, in open areas, around forest edges, and near rivers.^[1] This species prefers to live in areas with grasses, trees, and shrubs, likely because these areas make good places to build nests and to forage.^[1]

P. sericea colonies can range from a few to a few thousand individuals,^[2] but are typically made up of several hundred workers.^[4] The number of queens in a nest can range from one to several.^[2] New colonies are founded by swarming emigration, where the entire colony travels to a new nest site. ^[4]

Swarm emigration may occur for several reasons. One is if the colony sends a reproductive swarm from the original nest. This may happen if the colony has grown too big, and must split into two new colonies. In this situation, part of the colony remains in the original nest, with a subgroup leaving to colonize a new nesting site. Other reasons it occurs is if an old nest becomes unsuitable, or if the nest is attacked by a predator. At first, when the colony is driven from the nest, individuals assemble in groups of 2 or 3 around the original nest. Wasps will exchange between groups until the entire colony is assembled in one cluster. The colony may remain in this cluster for up to 2 days before migrating to the new site. Once the colony begins to travel, leading individuals drag their gasters over prominent objects such as branches or tall grass. This releases a pheromone that other workers can follow to the new nesting site.^[4]

Pheromone communication can be used to recruit workers to a food source, a new nesting site, or a place where work is required.^[8] The pheromone is released from the abdomen of the wasp, at the base of the fifth sternite. It is excreted by Richard's glands.^[4] The pheromone has a strong, leather-like odor, and looks like brownish wax.^[8] Because of the strong odor, workers can easily follow a pheromone trail left by other colony members.^[4] The pheromone is produced slowly and continuously throughout life, so it can be used up if used too often or too quickly.^[2] Another species that exhibits this behavior is Synoeca surinama.

P. sericea individuals forage for flower nectar, nest-building materials, and for prey. Workers tend to search for building materials such as wood pulp in the mid-morning, and for food in the later morning and early afternoon. Workers generally forage close to the nest because they cannot fly long distances. These wasps can fly for about 75 m, which is low compared to other species in the genus Polybia. When searching over longer distances, return rate to the nest decreases. When availability of food resources is low, colony development becomes limited. P. sericea can store nectar as honey to use in times of scarcity.^[3]

When workers hunt for arthropods, they fly from side to side about half a meter off of the ground.^[9] Visual cues are used to determine where to search for prey, whereas olfactory cues are used to determine nearby prey, and elicit landing.^[1] Green and brown caterpillars are the most common prey for P. sericea. Once a caterpillar or other insect has been found, workers bite the insect behind the head. They then drag the prey up onto a twig or a piece of grass, or sometimes fly the insect to a different location, to keep ants or other insects from stealing their prey.^[1] Once the insect is in a safe location, the wasp malaxates (softens) it by mixing it with a thinner substance, presumably saliva. The worker then brings what it can back to the nest to feed others.^[9] If prey is too large to bring back to the nest, foragers leave the prey, and fly in side-to-side arcs back to the nest to recruit other workers to help carry the load.^[10]

Colonies of P. sericea are polygynous, and generally have more than one queen. Typically, the number of queens in a colony is three or four. This results in a lower degree of relatedness among workers, and why workers should care for offspring that are related to them by less than half is questioned. Although this is not fully understood, the advantages of group living may compensate for the low degree of relatedness among workers, so workers will still care for offspring.^[5]

Some morphological differences are seen between queens and workers of P. sericea. Generally, queens are larger than workers in the abdominal region, but have smaller head width and wing length. Queens are the only ones with well-developed ovarioles, mature oocytes, and sperm-filled spermathecae. Workers' ovaries are either underdeveloped or not developed at all, so they are not reproductive. Queens perform the reproductive tasks of the colony, while workers forage for food and nest-building materials. Thus, workers likely have larger brains and wings because they must hunt and forage for food.^[2] The morphological differences seen in this caste differentiation are also seen with the species Protopolybia chartergoides and Polybia rejecta.^[11]