Polistes metricus (metric paper wasp or metricus paper wasp) is a wasp native to North America. In the United States, it ranges throughout the southern Midwest, the South, and as far northeast as New York, but has recently been spotted in southwest Ontario. A single female specimen has also been reported from Dryden, Maine. P. metricus is dark colored, with yellow tarsi and black tibia. Nests of P. metricus can be found attached to the sides of buildings, trees, and shrubbery. [Nesting habits of P. metricus]
Like other Polistes species, P. metricus has evolved eusociality and demonstrates behaviors including nestmate discrimination and local mate competition. Like other hymenopterans, P. metricus has a haplodiploid genetic system. Nests of P. metricus have distinct characteristics like the ability to share nests with other Polistes species and reuse nests for multiple seasons. Another distinction is that P. metricus foragers take off from their nests in different directions depending on how long their trip will be. For short flights, they exit the nest flying horizontally, while for long flights, they exit the nest flying straight up to a high altitude before pursuing their direction.
P. metricus prefers to use soft-bodied prey, especially caterpillars, to feed its larvae.
Taxonomy This species was described by Thomas Say in 1831. Rau referred to this species as Polistes pallipes or P. fuscatus pallipes in a number of his publications. However, references to P. metricus as either P. pallipes or P. fuscatus pallipes are due to confusion with a dark morph of P. fuscatus, so the name P. pallipes is rather retained as a synonym of P. fuscatus and not of P. metricus.
P. metricus is found to be most closely related to P. carolina. The most recent phylogenetic analysis shows that both share a common ancestor with P. bellicosus.
Description and identification P. metricus has a dark ferruginous (rusty) color with black markings on its thorax and a mostly black abdomen. Its tibia is black, and the tarsi are yellow. A black spot, separate from the antennae, contains the three ocelli. Females bear six abdominal segments, while males bear seven."Paper Wasp." Project Noah. N.p., n.d. Web. 21 Nov. 2013. Swelled parts of the abdomen of this species are a key defining element.
In the female, extensive rust-red coloration occurs on her head and mesosoma. Female P. metricus yellow markings are very limited in area. The mesosoma has a large spread of red color, and the metasoma shows black coloration. P. metricus also has an especially marked outward bend in sternum 2; however, this is often a very subtle characteristic. In the male, the red coloring takes up less area, but black coloration takes up more area. The male has more yellow markings than the female and a yellow color on his entire face and the pronotal carina. The yellow coloration on the legs of the male is highly variable in this species.
The smallest of the larvae can be told apart from eggs by noticing the darker anterior end of larvae. In the nests of P. metricus, cells that are capped are most likely cells that contain pupae. After pupae emerge from their cocoons, they leave behind evidence of their metamorphosis in the form of cocoon shavings.
Distribution and habitat The distribution of P. metricus is largely limited to North America. P. metricus has been spotted in the far southwestern reaches of Ontario, Canada. In the eastern United States, one female was seen in Dryden, Maine and recorded by the Canadian Nursery Certification Institute for pest control. This was a novel sighting for Maine, and probably indicated the beginnings of the spread of P. metricus into Maine. Other states where P. metricus is known to be located are on the east coast of the US, including New York, Pennsylvania, and the area from the southern part of Michigan all the way south to Florida; and the area westward to Nebraska, Kansas, Oklahoma, and the eastern part of Texas. Specifically, P. metricus has been studied in Brazos Bend State Park in Texas along with other wasp species, including Polistes bellicosus.
Preferred nesting sites P. metricus chooses its nesting sites based on shelter from the elements, size, lighting, and sources of water. It tends to build its nests in sheds and barns and on the underside of eaves. It especially prefers large and well-lit nesting locations. Its nests are mixed with those of P. fuscatus on a regular basis, and locations where one of them is present tend to also contain the nests of the other species, in close proximity to each other. P. metricus likes to use large bodies of water, such as ponds, as sources of water. In the summer, they frequently make trips to water sources for hydration.
Colony cycle Overview of the colony cycle The colony cycle begins in May and ends by October. The establishment of new P. metricus nests begins in early May, and this is typically performed by only one female; however, observed cases of colonies initiated by an association of foundresses have been observed. The colony slowly and gradually increases in size, and the average date for the first worker of the nest to emerge from its cocoon is in middle July. In July, the entire brood of workers emerges from its cocoons and this is also when the maximum rate of egg-laying of the year occurs. The next brood develops into males and reproductive females, and in September, these individuals also emerge from their cocoons. The survival of broods is reduced by parasitism from pyralid moths. The colony cycle typically ends by October. At this point, reproductive females leave their nests for hibernacula, locations where they spend the winter, and all males die.
Nest construction
Before July, nest construction surges ahead rapidly and the count of brood cells and the size of the nest both increase significantly. This period of speedy growth coincides with the emergence of the first brood of workers. Therefore, construction requires the input of workers. After July, the rate of cell building falls. It is rare to observe any vacant cells in the nest until late June. This is perhaps due to the queen's rate of oviposition being high enough to ensure all new cells get filled. However, due to the more rapid rate of construction between June and July, vacant cells begin to appear and become more numerous. This higher construction rate produces new cells faster than the queen's rate of oviposition. Then, in July and August, the number of vacant cells stays approximately constant. The rate of cell construction is the same as the queen's rate of oviposition. After August, vacant cell number increases significantly as the queen's oviposition slows down.
Polistes metricus has nests which grow slowly as the solitary founder may cannibalize eggs.Hunt, James, H. (2007). The Evolution of Social Wasps. New York, NY: Oxford University Press, Inc.
Egg production The rate of egg production fluctuates throughout the colony cycle. In May, the median egg count is greater than in early June. The yearly maximum point for the egg count occurs in July; egg production then decreases steadily to zero by September. Once the first brood of worker eggs has been laid, the queen decreases her rate of oviposition as this brood matures. Once they are mature, the queen stops laying eggs. In late June and July, the queen recommences laying eggs and her rate of oviposition increases once more. If the queen is killed, removed, or dies, workers can take over the responsibility of oviposition. In fact, 22% of an emerging brood comes from eggs that were not laid by the initial queen. Surprisingly, the final period of decreasing oviposition rate is not due to old age or mortality of the queen. It is actually due to ovarian diapause that occurs throughout the entire female population of the colony.
Larvae and pupae populations Two peaks occur in the number of larvae present in the colony. The first peak occurs in early June, coming right after the peak egg count. The second, highest peak of the larval population happens in July at exactly the same time as the highest peak in the egg count. This is probably so closely matching because eggs hatch into larvae very quickly in July, when the temperature is high. The median count of larvae decreases slightly in August and then rapidly decreases to nothing (zero) in September. The speedy fall in larval population happens because larvae pupate, and late in the season there is increased parasitism of larvae and brood destruction wrought by the adult wasps. In early June, the first pupae appear. Compared to eggs and larvae, the pupal population seems to only have one maximum. The pupal instar has a duration of 18–26 days for P. metricus.
Adult female and male population In the beginning of the nesting season, the adult population typically contains only one adult female, the reproductive foundress. Cooperative co-founding of nests was once considered to be rare for P. metricus, but it now appears that this is becoming more common. Like eggs and larvae, the adult wasp population of P. metricus has two maxima. The first peak occurs in July and corresponds to the emergence of the first brood of workers. These workers used to be pupae in late June, and were also the first peaks of the eggs and larvae. The year's maximum count of adult females and males is in September. This is the last brood of adults and the females in this group become the next season's foundresses and overwinter in hibernacula.
Foraging flights P. metricus has a very distinctive foraging behavior compared to other wasps. Adults search for prey in low-level vegetation, shrubs, and trees. When they embark on long flights, they tend to have trees as their destination. Their pattern of flight when leaving the nest reflects the nature of their journey, as if they already know in advance the distance that their flight will take. When they wish to fly short distances, they exit the nest with a horizontal trajectory, just above the upper edges of the vegetation, and usually between 1.0 and 1.5 m above the ground level. When their flight involves greater distances, they leave the nest, flying 3 to 4 m above the ground when flight distance is about 10–15 m. Extremely long flights greater than about 100 m involve the wasp flying at high altitude, measured at 17 m, and these wasps make their climb very quickly upon taking off from the nest.
In the summer, reproductive females (gynes) fly significantly shorter distances to forage than do their worker counterparts. When a P. metricus wasp locates prey, she typically will return to the same location and search the same sites at the location on future foraging trips. This is probably because predation by P. metricus is not sufficient to dramatically reduce the prey population at the site. Compared to other paper wasps, P. metricus tends to forage over longer distances. This may be due to less tolerance of P. metricus for prey scarcity, or that when prey is scarce, P. metricus is inefficient at capturing prey. On a longer flight, once an abundant source of prey is detected, P. metricus can efficiently forage for the long-distance prey. Longer flights are facilitated by the greater average size of P. metricus compared to other paper wasp species.
Malaxation