Native fauna thrives at Seychelles' Vallee de Mai with 97% decrease in yellow crazy ants

SIF started monitoring the yellow crazy ants' population in Vallee de Mai in 2010. (Seychelles Islands Foundation)

(Seychelles News Agency) - Data collected by the Seychelles Islands Foundation (SIF) shows a 97 percent decrease in the yellow crazy ants - an invasive ant species - across the Vallee de Mai and Fond Peper on Praslin Island, resulting in an increase in native fauna.

SIF's science coordinator, Annabelle Constance, told SNA that at the moment yellow crazy ants are now concentrated in the buffer zone of the Vallee de Mai only.

"For three years now we haven't been sighting the yellow crazy ants in Vallee de Mai and Fond Peper, however, around the area where Vallee de Mai connects to the Praslin National Park, there are a few areas, that through our monitoring programme, we have seen that there is a percentage of yellow crazy ants, even if not in great numbers," said Constance.

She outlined that with the ants' distribution located at the periphery of Vallee de Mai, the baiting strategy of SIF has changed slightly, having moved to the buffer zone to prevent the species from being reintroduced in the two areas.  

She added that baiting at the buffer zone comes with its difficulty.  

"Within the buffer zone, there are a lot of boulders and we need to ensure that we can target the populations that live among these boulders. To do so, we try to target them twice a year," said Constance.

SIF started monitoring the yellow crazy ants' population in Vallee de Mai, one of the Seychelles UNESCO World Heritage sites, and Fond Peper on Praslin, the second-most populated island, in 2010. The foundation declared the situation an emergency in 2017 after seeing increases in the population and distribution each year.

In 2019, SIF started its intensive intervention, deploying a new type of chemical bait - AntOff - across the forest to control the invasive ants and reduce the impact on native wildlife.

Considered one of the top 100 worst invasive species in the Global Invasive Species Database, yellow crazy ants were first recorded in Seychelles on Mahe in 1962. The species rapidly spread to neighboring islands.

The presence of the yellow crazy ants in the Vallee de Mai has been of great concern for many years as it is home to the endemic coco de mer – the world's biggest nut. For the coco de mer to thrive, it needs a functioning ecosystem process where there is adequate pollination and a nutrient cycle. 

Since the significant decrease in the yellow crazy ants' population, SIF has seen a significant increase in the population of native fauna such as arboreal species, geckos, and mollusks. These species have been identified as important contributors to the ecosystem of Vallee de Mai and Fond Peper.

The ants attack wildlife with their formic acid spray, blinding much larger animals such as geckos and skinks, making the yellow crazy ants a threat to other species and to the fragile palm forest ecosystem.