Aride Island winning the fight against Big Headed ants |30 May 2016

Since August 2014 the Island Conservation Society has had an important project to eradicate the Big Headed ant (Pheidole megacephela) from Aride Island.

The project was funded with generous support from donors including the Christopher Cadbury Trust of UK.

It is too early to say with complete certainty but the eradication appears to have been successful. There is a marked improvement in some plants especially noted in the garden, due to the mealy bugs not receiving help, and the ground nesting birds are no longer being attacked.

The Big Headed ant is so called because despite its small size it has a disproportionately large head. It is a native of southern Africa and has invaded Seychelles including Mahé, Praslin, La Digue, Cousine, Cousin and Aride. It is omnivorous and will capture and kill invertebrates and small vertebrates including bird hatchlings.

The Big Headed ant (or BHA) is listed as one of the world’s 100 worst invaders as it forms a super colony under the earth, displaces all other beneficial ants and reduces the quantity of insects and invertebrates essential to the well-being of the forest ecosystem. They also have a mutual relationship with mealy bugs which feed on leaves and sap and can cause the plants to die. On Aride there was a moderate infestation of BHA — some trees were particularly affected by mealy bugs and were sickly, and ground nesting birds and fallen chicks were sometimes covered in biting ants.

Around seven hectares of the plateau and surrounding hills were treated with a poisoned bait which specifically targets the BHA, administered in small tubes to prevent birds and other fauna from eating it as a precaution. The bait is taken into the nest and after 72 hours, the whole colony dies. It was a long and hard battle to complete made more difficult due to the exceptionally wet weather in the past year, as the bait becomes inactive when wet. The final deployment was completed over Easter 2016. The initial surveys are very encouraging as no BHA are being found now and it is looking to be a great success. However, the whole area will be surveyed thoroughly over the next year to make sure there are no remaining nests, plus extra vigilance will be needed to ensure that BHA or Crazy Yellow ants do not arrive again with people and supplies. If the eradication is indeed confirmed this will be a huge achievement.

A special thank you goes to all the volunteers and workers who played a part in making this project a success and helping to keep Aride island a pristine Nature Reserve. If you would like to visit the island please check your bags for insects, lizards and seeds which could become invasive, negatively affecting the delicate balance of the ecosystem. 

Melinda Curran

Island Conservation Society