Polistes erythrocephalus

Male and female P. erythrocephalus are hard to distinguish unless they are observed at a close distance. Under close examination the abdomen of female P. erythrocephalus has six banded segments while male abdomens contain seven.[10] In addition the females abdomen narrows to a point with a stinger at the end. The male abdomen on the other hand is more rounded and does not contain a stinger. Female antennas also have 12 segments and are hooked at the end while males have 13 segments and have a more subtle curve.[5][10] It has been suggested that such sexual dimorphic traits within a species occur to make females more recognizable. This recognition makes it easier to kick males out of nests so that they can disperse and encounter more foundresses. Sexual dimorphism also allows males to more quickly recognize females, thus, providing the benefit of not having to waste time accidentally trying to mate with other males.[5]

Like most paper wasps Polistes erythrocephalus construct their nests by chewing plant and wood fibers with saliva to create a paper-maché-like material.[11] When dried, their nests are somewhat horizontal and due to the divergence of cells have a concave upper surface.[12] P. erythrocephalus nesting habits are very similar to P. annularis in that they prefer to build their nests in areas protected from direct sunlight, rain, wind, and other insects.[2] The locations in which they find this protection vary greatly from the countryside to the city. P. erythrocephalus in urban areas have been observed to build nests under the eaves of roofs, under the wood of basement floors, in barns/stables, under bridges, and in lofts. This species also appears to prefer to build nests in close proximity to a water source.[10] In more rural areas nests are found in clear areas such as the trunk of a solitary tree or the underside of a large Heliconia leaf. In these cases several nests can be built on the same tree at heights ranging from three to twenty feet off the ground. Again these nests are often in close proximity to a water source such as a stream.[2]

The founding phase begins in the spring and involves individual reproductive females (called foundresses) building new nests.[5] While one female founds the nest she is often joined by other foundresses several days later. In field studies, P. erythrocephalus were observed to have an average of 4.9 foundresses with a range of 1 to 10. If a foundress is not joined by other females within two weeks of starting the nest she will abandon her nest.[6] During the founding phase the foundress composition of any given nest changes daily as foundresses move from nest to nest.[5] In this way the foundress continues to reassess her reproductive options.[14]

During the worker phase in many Polistes species adult workers and early males are eclosed (emerge as adults from pupae). As workers emerge, they begin to assume colony tasks such as nest maintenance, foraging, and larva care. A typical P. erythrocephalus nest grows to contain around 95 cells. If a colony loses its queen or if she stops ovipositing, then all construction on the nest will stop. This is because the queens are the "primary initiators." While the workers may do much of the building and maintenance, queens with mature eggs in their ovaries demonstrate cell initiation behavior and are responsible for beginning the process.[5]

The reproductive phase lasts from the emergence of the first reproductives until the colony begins to decline and new reproductives disperse to form their own nests. During this time males wait on perches near nests in order to have the opportunity to mate with a virgin foundress. In some cases males will defend their perch in order to ensure the continuation of their genes. In the reproductive phase workers provide larva with food. This causes hierarchies among workers to emerge as more dominant individual workers forage significantly less than subordinates.[5]

In P. erythrocephalus the termination of nest growth and start of brood decline occurs when the queen ceases laying eggs or disappears. This demonstrates that the colony cycle of P. erythrocephalus is a function of the queen's reproductive cycle.[15] During the time between colony decline and the founding of new colonies, the initial colony begins to disperse as new reproductives search for locations to initiate their own nests. The foundresses of the colony often disappear as males accumulate in the nest.[5] Adults often remove paper from old nests and recycle it to use for new ones.[7]

As is common in many wasp species the queen of P. erythrocephalus nests has great influence over the behavior of the colony. The presence of an active reproductive queen in P. erythrocephalus is a necessity for normal colony expansion and nest growth. Under nutritional stress when an active queen is removed and a former inactive queen is substituted the brood will decline. However, under normal conditions when a queen is removed the nest can continue to grow (at a reduced rate) if there are workers present. These experiments demonstrate that the simultaneous presence of an active queen and an effective caste of workers have a huge effect on the success of the nest and colony. While it is often thought that a colony begins to decline with the cessation of the queen, this removal is often accompanied with an absence of workers. These two factors combined lead to colony decline.[15]

Polistes erythrocephalus nests of less than 50 cells contain no males. This absence confirms that only females accompany the reproductive queen (foundress) in the forming of a new nest. In nests of greater than 50 cells males begin to appear indicating that they are the progeny of the founding queen. The number of males in a nest increases as the number of cells increases until there is an equal ratio of males and females. As the number of cells in a nest increases so does the number of adults associated with the nest. While the number of females tends to increase proportionally more in smaller nests the sex ratio equals out in nests of 300 cells of more.[10]

As in many multifoundress wasp species, P. erythrocephalus foundresses compete viciously in order to become the dominant female. These interactions include chasing, biting, lunging, "sting threats," and aggressive mounting. Fights between individuals can sometimes even be fatal. These competitions lead to only one reproductively dominant female while the rest become subordinates. Once reproductive dominance is achieved then that female asserts great control over the behavior of the nest.[5]

P. erythrocephalus are predatory wasps and feed on a wide variety of larva. A colony's predatory capacity depends on the number of their own larva present in their nest rather than the number of adults present. They are known to prey upon hornworm larva and were observed to eat an average of 0.5 hornworm larva per day (maximum of 1.3 and a minimum of 0.08).[10]

The starvation resistance of P. erythrocephalus was tested on both adults and larva. Adult P. erythrocephalus demonstrated average resistance and died in two to three days when cut off from food and water. The larva of P. erythrocephalus however proved to be extremely starvation resistant. In one nest six larva were found alive after 26 days without any food or water. After this time one of the larva was minced and fed to the remaining larva which ate it readily. This demonstrates that the larva will behave cannibalistically when necessary.[2]

One of the most devastating predators of P. erythrocephalus are army ants such as Eciton burchellii. These ants attack wasp nests and consume the larva and pupa, often destroying the nest in the process.[16] P. erythrocephalus has not been observed to have any ability to defend their nests from such predators. However, they will attack and sting larger slow moving threats such as humans if they get within 1–2 meters of a nest.[16]

The most common symbiont found in P. erythrocephalus nests is Pachysomoides stupida, a type of parasitic ichneumon. Papery cocoons of Pachysomoides stupida are found in many P. erythrocephalus nests while adults are seldom found.[2] Other parasites of P. erthrocephalus include some species of Oxysarcodexia or flesh flies and Brachymeria conica (Brachymeria is a parasitic wasp genus). Both these species parasitize the larva and pupa of P. erythacephalus.[10] Additionally, some Xenon species parasitize P. erythrocephalus adults, acting as permanent entomophagous endoparasites by dwelling in the abdomen.[10]

Microlepidoptera (types of smaller moths) larva have been observed to feed on the excretory waste of wasp larva.[2]

Polistes eythrocephalus is not commonly observed to tend or collect honeydew from aetalionids (treehoppers) or any other insect species. Honeydew is a good source of carbohydrates, composed of a mixture of oligosaccharides. This mixture provides those that eat it with an energy source higher than that of floral nectar. However, in one study done in Peru researchers observed a single female P. erythrocephalus among an aggregation of Aetalion reticulatum (treehoppers). The female P. erythrocephalus stood among or below the treehoppers and touched them with her antennae. Though they did not directly feed her, the honeydew accumulated below where the A. reticulatum were standing. P. erythrocephalus then collected the honeydew from the branch. This research provides the first bit of evidence that P. erythrocephalus may tend to aetalionids within its range.[17]

A number of species take advantage of abandoned nests. An unidentified species of Trypoxylon (a mud-daubing sphecid) uses the cells in order to raise its own brood. Moths of family Phycitidae use the cells as a safe place to form a cocoon. Spiders of families such as Salticidae, Linyphiidae, Oonopidae, and Scytodidae have been observed to use the nests for brooding and resting webs.[2]