John Midgley looking for larvae in rot holeCredit: Kurt Jordaena
A clear plastic container holding watery yellow-brown termite faeces has pride of place in the office of dipterologist, John Midgley, at the KwaZulu-Natal Museum in South Africa. He often searches the muddy glop for signs of the larvae of an African hoverfly, Meromacroides meromacriformis. He hopes to shed more light on how this little-known fly species, first found some 160 years ago, develops.
Throughout those 160 years, only three research papers have ever been published about this fly. Due to the limited number of researchers specialising in the study of flies in the content, there has not been enough work done to understand the Meromacroides meomacriformis — much like the 20,000 other fly species in the region that are understudied or the 200,000 that are still undescribed, says Midgley.
It’s only in the last three years that Midgley and others studying African fly species have realised that termite excrement, called frass, collecting along with rainwater in the hollows of slow-growing trees is the preferred habitat for this hoverfly’s larvae.
“It’s the only fly species we know of that is so specifically linked to termites in this way,” says Midgley. The wood-eating Schedorhinotermes lamanianus termites enter a tree through a crack or hollow. There, they continue to live, feed and excrete. The female Meromacroides meromacriformis lays eggs within the build-up of termite frass, and once the termites eat a tree from the inside out, it dies; destroying the fly’s breeding ground.
Meromacroides female hovering in rotholeCredit: Terence Bellingan
Midgley says very little is known about the developmental stages of most of the 610 to 650 species of African hoverflies. “Once we have enough larval descriptions, we will try to make an identification key and start comparative studies.”
Midgley is one of three dipterologists in full-time employment in South Africa, and there is another in Benin. Postgraduate students or experts based at international institutions do most other research on African flies – but even so, they are a mere handful.
Meromacroides meromacriformis specimens, for instance, have been collected 27 times in the past century and a half, from areas ranging from KwaZulu-Natal in South Africa to Kenya in the North East and Benin in the North West. This suggests that the fly is widespread, but exists in quite low densities.
“It probably only lives in old forests with suitable trees for its larvae to develop,” Midgley suggests.
Yet, only three scientific papers mention the species. The first is a 1915 paper in which the Italian zoologist Mario Bezzi named and described it, based on a single male specimen collected in South Africa and then housed in the Natural History Museum in London. According to a handwritten note accompanying the specimen, British botanist, Robert Plant had collected ir specimen, possibly in KwaZulu-Natal, where he had done collection work between 1854 and his death in 1858.
A second paper, published in 1927, touches on species collected in the Congo by an American expedition. The third followed nearly 100 years later, in 2021, in African Invertebrates. Led by Terence Bellingan of the Albany Museum in Makhanda, South Africa, the paper describes for the first time a female specimen, which is slightly bigger and more robust than the males.
Meromacroides maleCredit: Kwa-Zulu Natal Museum
Meromacroides femaleCredit: Kwa-Zulu Natal Museum
The African Invertebrates paper focuses on specimens that Midgley and Bellingan collected in November 2020 in a protected coastal forest in KwaZulu-Natal while doing fieldwork as part of the Diversity of Pollinating Diptera in South African Biodiversity Hotspots project. They had been looking for another rare hoverfly, Syritta rufa. It remained elusive, but during the search Midgley picked up on the buzz of a single fly coming from inside a wild frangipani tree (Voacanga thouarsii).
“I turned, and there was a fly hovering inside a rot hole. As it came out, I caught it with my net,” he recalls. It took a week to identify. The only other known specimens from South Africa were, after all, collected in the 1850s and were now in England.
The idea that the hoverfly’s life cycle is tightly bound with frass from rot-holes where termites are active was mentioned almost in passing, in their subsequent African Invertebrates paper about the find.
A fieldtrip in March 2022 to Kosi Bay, some 300 km from Mtunzini, in the company of DIPoDIP lead, Kurt Jordaens of the Royal Museum for Central Africa in Belgium, has since helped to flesh out these concepts.. They saw a Meromacroides meromacriformis hovering around a rot-hole at ground level in a slow-growing Pterocarpus angolensis teak tree.
The thinking now is that male Meromacroides meromacriformis hover around appropriate trees to increase their chances of mating with a female searching for frass-filled habitats to lay her eggs.
“The male guarding a site is normally the biggest one around. It will be stronger, fitter, and have better mating opportunities. This in turn gives the female the benefit of the strongest possible offspring,” Midgley says.
He hopes that the species will be officially recognised and conserved as a rare species. Information boards will be placed near the Mtunzini and Kosi Bay collection sites, which both lie within a protected area and within easy access to the public.
Good fortune, Midgley concedes, played a role in most recent fly discoveries made in Southern Africa.
Persistent rains in mountainous Lesotho, for instance, once forced Midgley and dipterologist Burgert Muller from the National Museum in Bloemfontein, South Africa, to replace their regular flight-interception traps with nets to beat bushes. They collected many Atherimorpha latipennis and a specimen of what Muller initially thought was a flightless moth. This turned out to be the first female of the species yet collected and described. It had stunted wings, and therefore couldn’t fly – a rarity for a fly.
The entomologists worry that climate change and rising temperatures will influence the mobility and survival of many species. While some could migrate to higher terrain, this strategy isn’t an option for high altitude specialists such as Atherimorpha latipennis that can move nowhere higher.
“The rapid pace of climate change may eliminate populations of the fly. Knowing the female changes how we interpret threats to this species,” Midgley says.
