Fighting the scourge of the Yellow Crazy Ants

Yellow Crazy Ants, or YCA (Anoplolepis gracilipes), were first identified on Mahe in the 1960s and a decade later on Praslin. In 2009, they gained more notoriety as an invasive species, posing a threat to two Nature Reserve on Praslin: the UNESCO World Heritage Site, the Vallée de Mai, and Fond Peper. With their unique zigzagging movement, YCAs have an effective method of infesting areas by hitching rides with humans or any other means of transportation, allowing them to travel long distances and form super colonies with one or more queens. Additionally, this long-legged ant uses formic acid to paralyze and kill other species, regardless of their size. These characteristics render this species difficult if not impossible, to eradicate.

In 2023, following a possible identification, ICS introduced mandatory surveys to detect the presence of YCA on all of the six islands/atolls with a permanent presence. Following this, three islands - Alphonse, Desroches and Farquhar – confirmed the presence of YCA, prompting the Conservation NGO into action.  

​Desroches Island
On Desroches, the team identified YCAs in an area close to the tortoise sanctuary. This was immediately demarcated, and bait stations with small portions of jam were placed throughout the infested zone. Global Positioning System (GPS) points were taken to monitor eradication progress. By November 2024, the team had not recorded any more YCA on the island. “We acted quickly and effectively, and with the help of our partners, we have so far been able to prevent a re-introduction of YCA,” states Elisabeth Hein, the Conservation Officer on Desroches Island. However, the team is still cautious of a reintroduction through regular boats or flights that arrive on the island and remains vigilant in their monitoring of YCAs on the island.

Farquhar atoll
Farquhar Atoll presented a different challenge due to the extent of the infestation of YCA. Under the leadership of Seychellois Conservation Officer Priya Didon, the ICS team deployed jam bait alongside additional baits, such as Hymenopthor and Fipronil in heavily infested areas on Ile Du Nord where the human population lives. A colony of the Red-footed Booby (Sula sula) – a seabird species nesting on Ile Du Nord– was especially vulnerable given its proximity to the infested areas. Other small uninhabited islands of the atoll have so far remained unscathed. With the infested area demarcated, the team has so far deployed over 700 jam-baiting station on Ile Du Nord. “We are focusing on areas where the presence of YCA is confirmed. Other than that, we only use jam to check for their presence,” Didon states. However, heavy rainfall has hindered their progress, and the team is eager to get the situation under control.

Alphonse Group
On Alphonse, YCA was first detected in 2018 and more recently, has been spreading rapidly. Last year, the team launched a rigorous survey to identify the most infested areas on Alphonse, the main island in the group. According to the Conservation Officer Jack Coupland, the team deployed over 1,168 jam traps out of which 100 had one or more YCA in it. “The broad-scale baiting has helped us to identify areas where the ants are present. Now we are streamlining our efforts into a more localized bait deployment which will significantly reduce the population of YCA in a short period,” states Coupland. ICS is also relying on the expertise of its partners, including the hotels on the respective islands and the Islands Development Company (IDC) in this rigorous exercise which will also include using pesticides in areas where there are human residences and minimal risks to biodiversity. “This is a long-term eradication that will take different methods and concerted efforts by all the partners,’ adds Coupland.

Aride Island
Although Alphonse, Desroches and Farquhar, are the only islands with confirmed YCA infestations, ICS remains vigilant. Monthly surveys are now mandatory for all Conservation Centers, including Aride Island, a Special Nature Reserve which welcomes daily visitors from other islands. “We have amped up our biosecurity measures in view that there is a serious threat of YCA coming on Aride from Praslin,” states Emma Cotton, the Assistant Conservation Officer on Aride Island. “All visitors to the island are encouraged to bring as little as possible and should they disembark with bags, these are thoroughly searched for ants and other pests.” She adds that these measures will hopefully keep the ants away from the island which is an important nesting place for various species of seabirds.
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The impact of Yellow Crazy Ants (YCA) on biodiversity cannot be overstated, and the human and financial resources required for successful eradication are substantial. The control methods and protocols applied on islands with confirmed YCA infestations by ICS, demonstrate that only sustained commitment and significant investment can lead to their eradication.