Ropalidia Social Wasp

I found two foundress Ropalidia species of paper wasps, initiating a new nest on one of the granite pillars of my courtyard. I used my Canon EOS 5DS R fitted with Canon MP-E 65mm f/2.8 1-5x Macro lens, lit by Canon MT-24EX macro twin light flash with a DIY diffuser to capture these wasps and their nest. These captures shows 6 days old nest. Eggs are still growing and adults haven’t emerged yet from the nest. They were caring for the nest for another 3 days after shooting these shots. Then both the females suddenly abandoned the nest completely and did not return to care the nest. The eggs perished and became food for foraging ants.

The social wasp genus Ropalidia, a primitively eusocial species occurring in the tropical climate of southern India and exhibiting a perennial, indeterminate colony founding cycle. As in many other species, new nests are initiated by one or a small number of female wasps. Ropalidia belongs to the family Vespidae, subfamily Polistinae, Tribe, Ropalidiini. The genus Ropalidia is unique because it contains both swarm founding species, meaning that new nests are founded by a large group of workers with a smaller number of inseminated females (egg-laying queens), as well as independent-founding, meaning that each nest is founded by a single queen.

On the Indian subcontinent, there are 22 recognized species of the genus Ropalidia. Ropalidia cf. marginata are a dark reddish colour, with yellow spots on some joints and a yellow ring around the lower abdomen. Males differ from females by having a weaker mandible and lacking a stinger. The female workers are not morphologically different from the queen and are more distinguishable by behaviour. Females are hard to distinguish morphologically except for their level of ovary development, which generally increases with their age. Females are the default workers of Ropalidia, but they may also rise to queenship by taking over a resident queen, founding a new colony, or adopting an abandoned one.

Ropalidia nests are made of paper like material, which are produced by wasps masticating cellulose and mixing it with saliva. The nests are usually found in closed spaces with small openings in natural and man-made structures. In India, Ropalidia marginata has an aseasonal, indeterminate and perennial colony cycle, which means that nest initiation starts throughout the year, and nests are active throughout the year. Colonies are started more frequently from May to July when food is abundant and less frequently from December to February when temperatures are colder.

The distribution of Ropalidia extends as far west as Pakistan and as far east as New Guinea, Queensland, and some eastern Pacific islands. They are the most common social wasp in India.

Female workers forage to feed themselves and non-foragers, such as the queen, larvae, and males. They help to build the nest and care for the larvae. Workers may mate with males and remain inseminated even if they are never able to attain queenship and produce offspring.

When a queen is lost, a worker has the ability to take her place. The mechanism by which the next-in-line-queen is chosen is cryptic; neither age nor dominance accurately predicts the successor. The potential queen may or may not be inseminated or have developed ovaries. The only certainty is that after the queen is gone, the worker who is the potential queen will become very aggressive. The aggressiveness subsides after about two days. The potential queen seems to require this heightened aggression in order to boost her own development.

Males are produced less frequently and in less quantity than females are produced. After eclosion males remain on the nest for up to a week. Upon leaving, they live nomadically and mate with females of other nests and then die. Males do not assist in any of the colony maintenance activities while they reside in the nest. They are not well suited for foraging or defending the colony because of their weaker mandibles and lack of a stinger. They are totally dependent on female workers feeding them and are sometimes observed to cannibalize nest larvae.

Primitively eusocial societies are typically headed by behaviourally aggressive queens, who use aggression to suppress worker reproduction. However, the queen in Ropalidia marginata which what this wasp looks like, is a “docile sitter” who does not use physical aggression to maintain her reproductive monopoly in the colony. The queens are suspected to control workers through pheromones. She uses these pheromones to signal her presence and fecundity to her workers, who perceive these signals and refrain from reproducing. The tenure length, age, and productivity of a queen varies greatly on a case by case basis. She does not regulate worker behaviours such as foraging and nest maintenance.

Each colony has one reproductive female, a queen, and that position can be taken by adopting an abandoned nest, taking over queenship at an existing nest, or starting a new nest alone or with other foundresses. The amount of time it takes for a brood to fully develop is highly variable and is complicated by occurrences of nest cannibalism, which is often undetected as replacement eggs appear. Tenure on the nest for a worker female is more variable. Their residence time ranges from 1-60 days.

Colonies can be started most frequently with four or less foundresses. Although the multiple foundress colonies were less likely to fail, all colonies, regardless of number of foundresses, had the same per capita productivity. Only one individual acts as an egg layer in each colony.

Individuals may migrate from their birth or founded colony to take up residence in another. This is most common during the pre-emergence phase and when there are around forty to fifty adults on the home nest. Migrant wasps are more likely to be accepted while they are younger, which is generally less than six days old. Age has been shown to be the determining factor for whether the resident wasps react with hostility or tolerance.

Females feed larvae by masticating acquired solid food for three to four minutes before feeding it to the larvae. She feeds about two larvae the solid food and then grooms herself. Then she feeds six larvae with a liquid of regurgitated food and grooms herself again. Females also engage in behaviors such as fanning wings, antennal drumming, and body jerks which are sometimes synchronous between many females. These behaviours are expected to be related to adult/larval communication.

Vespa tropica, the greater banded hornet, is a key predator of Ropalidia brood in Indian populations. As a predator avoidance strategy, nests are often built to only be accessible through small openings, thus, preventing hornets from getting through.