A new species of black and green social wasp, Ropalidia jemmae, was discovered in the Ambohitantely and Ankafobe indigenous moist evergreen forests of Madagascar.Credit: Len de Beer
A recently identified species of black and green Ropalidia social wasp from Madagascar throws the design handbook for its genus out of the window.
According to a study in the Journal of Hymenoptera Research, its inverted ‘upside down’ design differs markedly from the more rounded, three-dimensional nests typical of other Ropalidia. These are usually built up of hexagonal cells that touch other compartments on six sides, with easy access from the front.
At first glance, Ropalidia jemmae’s nest looks like a flattened piece of grey-green lichen set against a tree. The entrance to each nest cell faces towards the tree trunk, while the cell bases, pointing skywards, form a flattened ‘roof’ under which up to 30 adult wasps hide.
While some American social wasp species also build inverted nests. Ropalidia jemmae is the first outside the continent discovered to use this method to construct them, says lead author and entomologist, Ozren Polašek, head of the Croatian Science Foundation.
He says inverted nests require more building material, and therefore more time and effort to build than more effectively shaped, geometrically aligned nests.
To the untrained eye, Ropalidia jemmae’s nest looks just like another piece of lichen growing on a tree.Credit: Len de Beer
Like many other Ropalidia species, Ropalidia jemmae uses lichen to construct and hide its nest from ants, beetles, other wasps, and birds, that could raid their brood. The flattened roof of its nest, set against a tree, makes it even more inconspicuous.
“This all makes the nest look like a regular lichen growing on a tree trunk,” says Len de Beer, an entomologist, who works for the Eden reforestation project in the Malagasy indigenous forest of Ambohitantely.
De Beer and his colleague, Tahina Rakotodranaivo, first noted the insect and its nest in October 2022, while they were exploring another nearby endemic forest, Ankafobe. He loaded photographs on to the citizen science platform, iNaturalist, hoping to attract some expert opinion, and thereby connected with Polašek. Polašek says that green patches on an Ropalidia jemmae’s 1,5 centimetre long, mostly black body further camouflages it from predators.
“These green elements suggest that visual predation is an important evolutionary force here, as opposed to the bright black and yellow of social wasps in the temperate regions,” he notes.
Over 500 adults live in the mature nests of some Malagasy social wasp species, but only around 30 adults seem to do so in Ropalidia jemmae colonies.
The new species is named after De Beer’s daughter, Jemma, who helped to search for more specimens of the wasp.
Madagascar is often referred to as one of the world’s “last Edens”. More than 80% of its species are found nowhere else. It has more unique species than any comparably sized landmass, according to the Zero Extinction website. A 2021 paper in Nature Ecology and Evolution listed Madagascar, Brazil, Indonesia and Colombia as the four countries where new species of terrestrial invertebrates are most likely to still be discovered. Only a quarter of species from these regions are estimated to be known.
De Beer described Ambohitantely and Ankafobe forests as “tiny, fragmented biodiversity jewels” that provide irreplaceable homes to various endangered, endemic species, many of which might still be undiscovered. He urged for adequate conservation of Madagascar’s forests without which the newly discovered wasp species could “go from being undescribed to described to endangered in a very short space of time.”
Polašek was lead author of another new Ropalidia discovery described in the Journal of Hymenoptera Research. Ropalidia amabala, found in South Africa’s Eastern Cape province, is the first known member of the genus found outside Madagascar to also use lichen to construct its nest directly on to a tree trunk.
Ropalidia amabala’s name refers to the Zulu word “amabala” for “spots”, in reference to the six characteristic spots on its abdomen. Whitish-yellow markings on its dark brown body further help the wasp to blend into its surroundings.
Evolutionarily it does not seem to be closely related to Malagasy Ropalidia. This suggests that nest protection by visual concealment in this genus evolved twice over, once in Madagascar and once in South Africa, says Polašek.
