A look at the behaviours and nest-building strategies of Ropalidia paper wasps.
There are a number of Australian wasp species belonging to the genera Polistes and Ropalida. Whereas Polistes species have a broader distribution, Ropalidia is primarily a tropical, eusocial genus. Two common species of Ropalidia found in Queensland include R. revolutionalis, the stick nest brown paper wasp and R. romandi, the yellow brown paper wasp, which encloses its nest in a ‘paper bag’ of cellulose material – ‘The Piñata of Peril’. However, there is one temperate species of Ropalidia found in Australia, R. plebeiana, which has a very unusual nesting behaviour and colony structure.
The tropical species of Ropalidia generally produce queens at any time during the year and nests will contain multiple reproductive females. This is common in tropical wasps, where the climate is less seasonal, and colonies are more flexible in their reproduction to respond to changes in local conditions. R. revolutionalis is an independent-founding wasp species, where new nests are founded each spring by a single queen or small group of females (main image, above). R. romandi also has multiple queens in the colony, but it is a swarm-founding species, with nests persisting through the winter to grow year on year. However, the colony structure of the temperate R. plebeiana is very different.
R. plebeiana colonies are started by one or more foundress queens in spring. However, one female will become dominant and the egg layer. They build small, single vertical combs in sheltered areas, such as under bridges or cliff overhangs. Sometimes you may observe a large number of vertical combs together in what looks like a massive nest, sometimes comprising thousands of combs. However, this is actually an aggregation of different colonies. It is extremely rare for any social insect to have such dense colony aggregations where the distance between colonies may be as little as a centimetre.
Individual nests grow during the year with new reproductives produced in autumn. The colonies die off in winter with the new queens overwintering (in undetermined locations). The following spring these foundress queens often return to their natal nesting site to reuse the old combs. Each queen cuts off a piece of the old comb to set up a new colony, often with other females. The interesting finding from recent research is that the group of females creating each new colony showed a strong degree of relatedness, certainly stronger that the degree of relatedness between new colonies. The researchers concluded that the wasps were able to recognise their kin, and related individuals often worked together in comb-cutting behaviour and colony founding.
This cycle is repeated each season. As a result, for a favourable nesting site, the number of returning wasps increases each year, resulting in more combs and the large aggregation of nests.
Further reading: Tsuchida, K., Ishiguro, N., Saito-Morooka, F. et al. Nepotistic colony fission in dense colony aggregations of an Australian paper wasp. Sci Rep 12, 12868 (2022). https://doi.org/10.1038/ s41598-022-17117-y