Polistes gallicus

P. gallicus, like other members of the subgenus Polistes (Polistes), has recognizable, bright yellow and black markings. They have smaller bodies than many of its allies that overlap in range, and their bodies are largely hairless.^[3] The species may be separated from allies through the following traits.

Females are identified by having 12 antennal segments and 6 abdominal segments. The antennae are orange and paler on the ventral surface than in many allies and have yellow-marked scapes. The malar space is short, under 0.75 times the distance between the lateral ocelli, and is black. They have slender mandibles that are mostly colored black with an excentric yellow spot on each. In contrast, the clypeus is yellow and often with a small but distinct black spot or band. As in many species within the subgenus, the mesoscutum has a pair of developed spots. Both the spots on the propodeum and continuous band on the fourth abdominal sternite are wide. Unlike species such as P. dominula, P. gallicus has a mostly black hypopygium.^[4]

Males are identified by having 13 antennal segments and 7 abdominal segments. The head is roughly triangular as viewed from the front with a curved clypeus. The apical half of the antennae is entirely orange-yellow, and the final segment is slightly under twice as long as wide. The pronotum has a yellow band that widens toward the sides as well as short, straight hairs. The mesosternum is largely yellow, more so than in some allies. Both the mesoscutum and scutellum typically have distinct spots. The abdomen has the final sternite entirely black.^[4]

P. gallicus is a member of the family Vespidae, further classified under the Polistinae (the second-largest of the subfamilies), which consists of various social wasps. Within the larger subfamily Polistnae, Polistes species are categorized by their independent founding behavior, distinguishing them from swarm-founding species.^[5] Furthermore, P. gallicus is one of about 200 species of wasps in the genus Polistes.^[6]

P. gallicus is one of 27 members of the subgenus Polistes (Polistes), which are typically very similar black-and-yellow species. This similarity has resulted in taxonomic complications in older literature. For instance, many references prior to 1985 misapplied the name to the European paper wasp, P. dominula.^[1] In terms of coloration, P. gallicus typically has yellow spots on the mandibles as well as a black hypopygium whereas P. dominula has often entirely black mandibles and always a largely yellow hypopygium.^[4] Additionally, many published studies for which no vouchered reference specimens are available cannot be reliably assigned to either species.^[1] P. gallicus is also very closely related to P. biglumis and P. mongolicus, which are members of the same species group.^[7] The former synonyms, P. foederatus and P. mongolicus, were restored from synonymy following revision of the genus in 2017 and are considered as distinct species again.^[4]

The range of P. gallicus extends across much of Europe, where it is a common species. It can be found from northern Italy and southern Switzerland south into northwest Africa and east to Croatia and Corfu.^[4] The species inhabits a variety of climates and habitats throughout this range, although it more frequently nests in warm and dry regions, where its nests are built hanging in the open with the cells towards the ground. In cooler regions north of the Alps, its nests are often built in more protective enclosures such as in pipes or metal scraps.^[8][2] Reports of P. gallicus in the New World^[9][10] are the result of misidentification or incorrect synonymy and actually refer to Polistes dominulus.^[11]

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Fertile foundress wasps come out of hibernation in the spring around mid May and build a new nest combining oral secretions with plant fibers, such as from sticks and bush branches, to make a paper pulp. A nest will begin to be constructed by late May to early April. Most nests are built by a single foundress, though in southern regions of Germany and Italy, two or more foundresses have been recorded building a cooperative nest. Each cell is formed in a hexagonal structure and are attached to a surface by a single stalk. The foundress will then lay a single egg directly in each brood cell. After about 2 weeks, the eggs hatch into larvae and are fed chunks of caterpillars, developing through 5 instar stages before pupating by spinning a cocoon to enclose its cell. Metamorphosis takes about 10 to 14 days before a mature adult wasp emerges.^[12]

This first brood of each season emerges around May to early June and is exclusively female workers that tend to the nest as subordinates to the foundress. They help maintain the nest, tend to the brood by hunting, and defend the nest if it's threatened. The foundress can now focus her time on laying eggs. Beginning with the second brood, the larvae are able to be better fed by the early workers and emerge as bigger adults. The nest continues to grow into the summer months as more cells are needed for the brood. This summer brood takes a single month to mature. The size of the nest can reach as many as 500 to over 1000 cells in optimum conditions such as sheltered, warmer locations, though they are still smaller than in allied species of Polistes. Such nests may have hundreds of workers.^[2]

By around June to July, some of the eggs laid by the foundress are willingly unfertilized so, instead of developing into female workers will more quickly develop into males. The females that emerge from around July to August, instead of contributing to the nest, instead store fat and develop their ovaries to become future foundresses. With the next generation of foundresses developing, the nest tends to decline in activity. When the original foundress dies, some workers may begin laying unfertilized eggs which, if they manage to develop, will be males.

The males that are produced congregate in unisexual clusters not far from the nest until November. They then occasionally mate with the future foundresses from other nests. As winter approaches, the workers and then the males die out, leaving only the newly fertilized foundresses to hibernate overwinter, in various shelters, until the following spring to begin a new colony cycle. This can be as many as two dozen, or more, foundresses.

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The wasp is omnivorous, feeding on fruits, flower's nectar, insects, snails, or larger animals' corpses. It feeds its brood after visiting numerous flowers, collecting nectar in addition to feeding them. Due to its dimensions, this species is suspected to transfer pollen to the stigma from its mostly hairless bodies, resulting in few to no pollen grains remaining on the body after foraging.^[3]

Hormones play a role in the establishment of dominance hierarchies among P. gallicus. Dominant females tend to have more developed ovaries due to higher activity levels in their endocrine systems. A larger corpora allata also influences the determination of dominance. A higher reproductive capacity is indicative of the dominant female.^[13]

After a hierarchy is established, the dominant wasp remains the sole reproducer in the colony due to the inhibition of endocrine activity within the subordinate wasps. Various factors contribute to the possibility of inhibition, which might also lead to differences in endocrine activity. If subordinates happen to lay eggs after the hierarchy is formed, the dominant foundress will recognize and eat the eggs to ensure all laid eggs are of her own lineage.^[13]

P. gallicus recognize their kin through Van der Vecht's gland secretions (VVS), which include a mixture of hydrocarbons that differ both between colonies and between the foundresses versus workers of a single colony. Workers can thus distinguish these differences, both to recognize their own foundress and to recognize wasps from another colony. In the case of alien wasps, workers may respond to these VVS with varying degrees of aggressiveness. Foundresses are also hypothesized to use peak activity in this organ as a repellant to defend the nest before it is populated. These VVS deposits on the nest may additionally indicate ownership to the queen and can inhibit ovarian development in the workers within the colony to prevent competition.^[14]

Colonies of P. gallicus typically have one foundress that produces offspring, though all females, including workers, are capable of producing male offspring. This creates a trade-off in terms of reproductive activity between the foundress and her workers. The relatedness of a foundress to her son is 1/2 as compared to a worker to her brother of 1/4. In the case of a foundress that only mated once, a worker's relatedness to a fellow worker's male offspring is 3/8. This closer relatedness to the workers means that workers may favor handling male production instead of the foundress. However, in the case of a foundress that mated more than once, the workers relatedness to a male produced by the foundress instead will be less than that of fellow workers.^[15] Because workers favor situations where the male brood are more closely related to them,^[15] workers may attempt to prevent other workers from laying eggs if the foundress has mated more than once.^[16]

As different colonies may have differences in the relatedness of workers, conflict over sex ratio arises. Fisher's theory of equal investment supports that a colony with a 50:50 sex ratio is the most beneficial due to both males and females having the same expected reproductive success.^[17] In colonies with an active foundress, workers may not produce male offspring of their own if it means a healthier colony. Additionally, a foundress may eat the eggs laid by workers to maintain balance if she was unable to prevent workers from laying eggs in the first place. The reverse is expected to occur as well. Indirect evidence also supports the occurrence matricide within colonies, and queen death is noted to be high in P. gallicus.^[15]