Ropalidia plebeiana facts for kids

The Ropalidia plebeiana is a special kind of wasp that lives in groups, like a big family. It's known as a paper wasp because of how it builds its nest. This wasp is unique because it lives in cooler areas, even though most wasps in its family, Ropalidia, prefer warm, tropical places. You can find R. plebeiana all over eastern Australia. Recently, people have seen huge groups of their nests, with thousands of them, on tree trunks in south-eastern New South Wales.

Where it Fits in the Wasp Family

R. plebeiana belongs to the Vespidae family, which includes thousands of other wasp species. The Ropalidia group usually has wasps that live in tropical areas, but R. plebeiana is different. Wasps in the Ropalidia group are often called brown paper wasps. Scientists have found that R. plebeiana is closely related to another wasp called R. proletaria.

What it Looks Like and How to Spot It

The R. plebeiana is a brown paper wasp with a white face. It's a medium-sized wasp with a reddish-brown body. You might notice small, thin white rings on its shoulders, middle section, and abdomen.

The nests of R. plebeiana look like a single, flat comb with an uneven shape. They are grayish-brown. Nests have been found with 1 to 3 males and between 13 and 28 females. These nests usually have about 40 cells, which have clear "windows." At any time, there might be about 20 larvae (young wasps) and eggs. The cocoons and larvae are found in the middle cells of the nest. These central cells are usually longer than the cells around the edges, which hold eggs. These wasps often build their nests very close together, almost like a "city" of nests. Different nests in these groups have been seen helping each other, but each comb is home to its own colony.

Where it Lives and Builds Nests

R. plebeiana is found across a large part of Australia. You can mostly find it in New South Wales and the Capital Territory. They are also in southern Queensland. The city of Brisbane is usually thought of as the northern limit for this wasp. However, R. plebeiana can also be found north of Brisbane in tropical highland areas, like the Atherton Tableland.

R. plebeiana is known for building its nests in large groups called aggregations. These groups are often found under bridges and under rocks that stick out. These aggregations are made of many separate nests built side by side. They were often built over running water. However, R. plebeiana nests in Canberra do not form these large groups.

The Wasp Life Cycle

R. plebeiana colonies usually have one main female who is in charge, or they are started by one or more founding females who then compete to lay eggs. New colonies begin in early spring in the Southern Hemisphere. The first group of worker wasps grows into adults by mid-December. New reproductive females and males appear in early March. These new females, called gynes, might become the founding females for new nests. Gynes don't usually stay in their original nest after they become adults, but they might spend the winter there. Most wasps leave the nest by late autumn, which marks the end of the nest's egg-laying period. Founding females in the nests don't stay overnight. They leave the nest before dark. Females return to the nest when the sun warms it up and start their daily activities. These patterns of leaving and returning depend on the nest's temperature.

How Wasps Build and Use Nests

Using Old Nests

Wasp nests can stay strong through the winter because they are often hidden from bad weather. Sometimes, the main female in charge will use a nest that was used before. They might return to their mother's nest to start their own colony there, sometimes with up to 10 other females. If this happens, the founding females divide the comb into their own nesting areas. Then, they fight to be the only one who lays eggs. Other females might stay as helpers. The first group of females born were larger than the founding females who didn't lay eggs. Using an old nest is helpful because females don't need to find materials to build a new one. They can also spend cold days and nights in the spaces between nests in a large group. There's a lot of competition for these old nests, and females who arrive early have an advantage. A female might lose the fight to be the main egg-layer at a nest, but she might stay to help her relatives or build her own nest nearby, adding to the big group of nests.

Nests with Many Founding Females

Founding females have developed ovaries (the parts that produce eggs). Those with only slightly developed ovaries are females who don't lay eggs. Founding females had fresh wings and mandibles (jaws), while other females (who didn't lay eggs) had worn-out, shorter wings and mandibles. The main body part of the wasp, called the mesosoma, is bigger in colonies with many females than in other colonies. Single founding females were smaller than those in colonies with many females. Once the females decide who is in charge, usually only one female lays all the eggs. However, in colonies with more than 20 founding females, there can be more than one egg-laying female. Nests built by a single founding female were more common in newly built nests.

Nest Aggregations

An aggregation is a group of nests built right next to each other. The nests in these groups often interact in different ways. Nests communicate with each other. The nests in an aggregation hang side by side from whatever they are attached to. Older nests might hang straight down. New nests mostly form along the edges of these large groups. R. plebeiana nest aggregations can last for up to 15 years! In these aggregations, each comb is a separate nest with its own females living there. Wasps rarely move between different nests. If a strange wasp tries to enter a nest, it is usually attacked and forced to leave.

Good and Bad Things About Aggregations

Being in a group of nests is very helpful for R. plebeiana. The survival rate for nests in an aggregation is very high, over 90%. The main benefits of living in groups are high survival rates for nests and many eggs being laid by females. However, there might not be enough food, like insects, for everyone. This means wasps might have to fly farther away to find food. One reason for these groups could be cooperation, or it could be that each wasp tries to protect itself by being in a big group. Also, the whole colony together might be better at defending against predators. But there are risks: if a new nest joins the group and doesn't help with defense, they could benefit while others do all the work. Things that can affect these aggregations include forest fires, which could destroy a whole group, cliffs collapsing, and attacks by predators.

Wasp Behavior

Dominant Behavior

In R. plebeiana, the regular nestmates don't usually act aggressively towards each other. The main female in charge might "dart at another but stop short." They also attack new wasps trying to join the nest. The main female might climb on the new wasp's body and try to sting it many times to make it leave. The attacked wasp might take a certain pose when attacked, try to fit into the nest, and sometimes succeeds. Sometimes, when females land on a strange nest comb in an aggregation, they leave right away without being attacked. Other aggressive actions by females include pecking, climbing on others, and biting. Sometimes these fights can cause a wasp to lose its ability to fly.

Foraging for Food

In R. plebeiana, the females, not the males, are the ones who go out to find food for the young wasps (larvae). Females also collect plant fibers to build the nest. The main female in charge doesn't directly go out to find insect meat; the other females do that. On their foraging trips, these females bring back solid food, honey, water, or pulp for the nest. Sometimes, the females give the meat pellets they collected to the main female, who then passes these pellets to the males. This way, both males and females help with feeding. Meat pellets are shared with other wasps back at the nest when the foragers return, and they are often given to males. Males don't ask for these pellets from females carrying food, but they are given to them.

Feeding the Young

The food for the larvae is usually insects. Females bring the food back to the nests and then share it. Females usually chew the food for a much shorter time, about 30 seconds, and then they feed several larvae with one meat pellet. Males, on the other hand, can chew for a few minutes, about 3 to 4 minutes, and then feed only one older larva during a feeding time. This feeding by males might mean they are taking liquid from the food, possibly to get rid of the pellet afterward. However, males of R. plebeiana were not seen getting rid of pellets, so more research is needed to understand this.

Female Actions

In R. plebeiana, especially in groups of nests, females were seen doing specific things in their own nests. Females repeatedly stick their heads into the cells where larvae are and vibrate their heads. This behavior was seen as a way for the females to check on the larvae. Females were also seen "kissing" to pass food or liquid between different members of the nest. When regular females "kissed" the main female, the main female got the larger share of the food. Females also "kissed" males to pass food to them, so the males could also help feed the larvae.