Angiopolybia pallens

The tropical social wasp genus Angiopolybia contains four different species. The wasp is within the tribe Epiponini and is a basal swarm-founding wasp. A swarm founding wasp is a wasp that finds its nest by sending out a group of wasps going out to find a new nest site.^[4] It is considered a eusocial wasp.^[6] Most social wasps have the unique characteristics of a caste system in which the queen wasp is the primary producer of offspring.^[7] This characteristic of a caste system is evident in the behavior of A. pallens. Lepeletier originally discovered the species in 1836. He classified the wasps under a different genus Rhopalidia and when he discovered the wasps he also found another species under the name of R. rufithorax. The species was later transferred to the genus Angiopolybia that shared with A. paranesis, A. obidensis, and A. zischkai. These species are widespread in the Amazon and extend from Costa Rica to Bolivia.^[2]

Angiopolybia pallens are distinguished by the ombre-like progression from yellow to black on their bodies. They have four legs that progress from a lighter yellow to a dark orange. The wasp's body is skinny with the back coming to a point.^[4] Their wings are slim and black. The slim wings cause A. pallens to fly low and for short distances. This means that their foraging area is limited to about 1,800 square meters.^[1] The workers, queens and intermediates of the colony are almost indistinguishable with the queens only occasionally being larger in size.^[4]

The nest of A. pallens is generally in a funnel shape with a downward facing entrance. The nest is usually attached to a leaf by a central pedicle. In general the nest is strategically placed at a diagonal in order to provide more coverage from a leaf. The nest is usually made from a mixture of salivary secretions and vegetal fibers.^[8] All social wasps use plant fiber as the primary material in the construction of their nests.^[4]

Angiopolybia pallens is predominantly found in Brazil.^[3] They are among the most common species of wasps in this area by an overwhelming amount, as seen in multiple feeding behavior studies.^[1][3] The wasps prefer more humid environments and are more active when humidity levels are higher. However, the wasps are generally more active during the cooler parts of the day, like the early morning or around dusk.^[1] The nests of these wasps are typically found in rainforest environments in clearings or on the edge of the forest. A. pallens typically have nests that are large and easy to see hanging off of the branch of a tree. This means that their nests are subject to predation by ants and other animals. In order to compensate for the size and easy sighting the nests are protected from any ant predation by arboreal ants with which they share the tree.^[8]

The colony cycle begins with the pre-emergence phase where the queen and a few adult workers establish a new nest. The queen already has been fertilized and is able to produce a few workers in the beginning in order to best assist with the building of the nest. The swarm starting the nest is mostly made up of adults that are already mature before the next nesting cycle begins. Then once the nesting cycle begins, the larvae and eggs are laid.^[4] Next is the worker production phase where they have the majority of eggs, larvae and pupae. This phase introduces the highest amount of reproduction and the intermediates are produced during this time. Once the nest and colony has reached maturity, the male production phase begins and the males eventually fertilize an intermediate. This fertilization distinguishes the intermediates from the queens and the colony cycle is repeated.^[4] The wasps are most active from months of July–December.^[1]

Angiopolybia pallens has exhibited a unique feeding pattern compared to most social wasps in a variety of ways. They are more active in the daytime compared to many other wasp species. These wasps tend to be most active at collecting nectar between 7 and 8 am, collecting prey between 10 and 11 am and collecting pulp for nest building generally happens before foraging. In general, other wasp species were found to start their activity later in the day and end earlier.^[1] A. pallens are usually the initial wasps present at the site of an animal carcass trap set by Silveira in an experiment conducted to study the wasps feeding patterns.^[3] The wasps also tend to collect nectar, prey and pulp in almost equal percentages. Other social wasps tend to focus on the collection of glucidic kinds of foods.^[1] This behavior still perplexes scientists.

Angiopolybia pallens have shown high prevalence of carrion feeding in Brazil. When compared to six other species of wasps, they made up 43.5% of the wasps that approached a carcass. The wasps do not transport pieces of flesh to the nest but instead consume at the feeding site, and the eaten food is subsequently regurgitated to other workers in the nest. The wasps also are more likely to consume carrion from July to December, which are the drier months of the year. It has been claimed that this wasp is the most important carrion consuming wasp in South America.^[3] An additional behavior that A. pallens exhibit is the interaction with other wasps and ants when feeding on carcasses. A. pallens are typically the first wasps to rush an animal carcass but are typically displaced when another bigger wasp species approaches the carcass. However, the wasps will hover over ants occasionally darting downwards toward them causing the ants to flee. The wasps will then land on that particular area of the carcass and feed. They continue to intimidate the ants preventing the encroachment on their space by raising their wings and darting towards the ants. In this way the wasps are successful at obtaining food from carcasses even in the presence of ants.^[7]

Swarming is often a method used by wasps to travel from one nest site to find a new nest site. This type of behavior is shown by A. pallens and is significant to note as it displays the importance of communication within the wasp colony. The wasps will divide themselves into two different swarms when beginning the process of finding a new nest site. The first swarm consists of queens and workers and this group leaves the nest site to find a new site to establish a colony. They leave the site because of “cyclic intracolony factors”, meaning it is time to move on and establish a new colony. The second swarm includes the rest of the adult population and happens upon the destruction of the previous nest. It is important to note that the queen is the founder of a colony as she is needed to produce new workers and intermediates to help fully establish the nest.^[5]

Once they have found a new nest site, A. pallens convey this information to other workers and intermediates through glandular secretions from their antennae. They make upward runs of several centimeters long on vertical surfaces providing a road map of sorts for the adult wasps to follow. The front body of the wasp will angle slightly upward while the antennae works its way upwardly to maintain the connection with the surface. The wings perk up as they make this connection. Typically A. pallens begins to use this trail about 3 hours after the swarm formation. This means that generally the new site is already being developed. In fact the dragging behavior seen to deposit the glandular secretion by the wasp is seen only after the deposition of building material at the new nest site.^[5]

The two primary causes of nest mortality for A. pallens and other social wasps is predation and inclement weather. Therefore, the wasps attempt to find a location that will both protect them from bad weather as well as bar any access for predators. Army ants present one of the largest threats as predators for A. pallens nest sites and are considered to be one of the driving forces in the evolution of their nest architecture. A. pallens have been found to build their nests near arboreal ants in order to help protect against the army ants.^[9] However, this does not mean that the wasps avoid predation all together. An evolutionary response to this chance of attack is the ability of the adult population to escape, move the colony, and replace the nest.^[5]