South African Paper Wasps - don't reach for the Doom!

South African Paper Wasps – don’t reach for the Doom!

By Dr Anina Lee

My covered veranda is a favourite spot for paper wasps. Their nests are dotted around under the eaves hanging like little upside-down umbrellas, sheltered from wind and rain. They are good at spotting a good spot.

Here in the Western Cape we have the paper wasp species Polistes marginalis. They are called paper wasps because their nests are made of something akin to paper. They chew up little bits of flaking wood and plant material and mix it with saliva. The resultant wood pulp is remarkably strong.

The most significant property of the wasp-produced paper is that it is hydrophobic and therefore waterproof. Research has shown that the nest paper is composed primarily of cellulose that is coated with a protein-rich oral secretion. In addition, the little fibrous stalk connecting the nest to the roof is coated with ant-repellent so that ants can’t prey on their larvae.

Paper wasps are social wasps. All the social wasps are gathered within the family Vespidae.

The social members of the Vespidae are generally divided into two groups: the Vespine wasps such as Yellow Jackets and Hornets; and the Polistine or Paper wasps.

The genus Polistes has a world-wide distribution and is the most common type of wasps in Europe and North America. The European paper wasp Polistes dominula has now also migrated to South Africa, where it is in competition with our native Polistes marginalis. Sightings of this invasive species should be reported to CapeNature or Overstrand Environmental Services.

Paper wasps have an interesting lifestyle. The nests are usually founded by a single queen. A mated female from the parental nest emerges in spring and starts building the nest. She becomes the queen and is soon joined by other mated females from the same nest to form a colony. The late-comers are relegated to the worker caste. After the queen has started construction of the first hexagonal cell of the nest, the worker females add more concentric circles of cells to enlarge it.

The queen will lay all the eggs. The worker females are destined to be the workers – building the nest, hunting for food and minding the offspring.

The queen lays an egg in the bottom of each cell. When the larvae hatch, the babysitters’ job is to protect them, sometimes aggressively, and to feed them. Unlike the spider wasps that parasitise spiders and lay their eggs inside the paralysed prey, paper wasps catch caterpillars, chew them up and present the minced meat to the larvae.

So in paper wasp society there is a division of labour – the older females procreate and the younger working-class females have to go out hunting to feed the kids. They prey on caterpillars, flies, beetle larvae, and add the odd spot of nectar. They forage during the day and rest at night.

When the larvae are ready to pupate and thus stop eating, the workers construct a paper-like lid for each cell to protect the pupae until they hatch.

In temperate climates such as South Africa, the wasps don’t need to hibernate, but start the next cycle of life as soon as they emerge from the pupae.

The females take on their different caste roles. The males are not much use at hunting, so they are fed by the females until such time as they are needed to mate with and fertilise a female. Then they die.

If the queen dies, the most aggressive female will become the new queen and begin to lay her own eggs. In late summer or autumn, males, unmated females and the founding queen will all die. Mated females will go forth to form colonies of their own.

So if you see a paper wasp nest under the eaves, do not reach for the Doom. They are not aggressive and will not attack you. They are keeping the ecosystem in your garden in equilibrium, by preying on insect larvae and aphids.

Aphids were for several years a big problem in my lemon tree. They were farmed by ants who tickled them until they secreted a sweet ‘honeydew’. This production of sticky sweetness soon caused the growth of black fungus all over the tree. No amount of fungicide or ant poison helped – it only harmed the environment.

Lightbulb moment! Smear a ring of Vaseline around the trunk to stop ants going up the tree. Problem solved – no farmed aphids, so numbers are lower and perfectly managed by the wasps. Now I see my wasps buzzing around the lemon tree, inspecting every leaf for the first sign of aphids. My perfect biocontrol buddies. I love a well-balanced ecosystem!