Invasive crazy ants threaten ecology, traditional customs on Orchid Island

Ecologists are warning that yellow crazy ants (Anoplolepis gracilipes) have been found to be already established on Orchid Island, threatening a local species of land crab, and cultural workers say it could also affect important traditional customs of the indigenous Tao people.

Professor Lin Chung-chi, an ecologist from the biology department at National Changhua Normal University recently led a team of students and researchers to the island, and found that the crazy ants are already established on the island.

The research team also received a disturbing report from a local high school teacher, saying that the ants were found to be eating the meat of land crabs.

Residents have found dead land crabs with yellow crazy ants consuming the flesh of the crabs.

Crazy ants have caused significant damage to land crab ecology in parts of Pingtung County, Taiwan, and on Australia’s Christmas Island, Professor Lin said.

While the crazy ants don’t actively seek land crabs as food, when a crab enters the colony’s defense territory, the ants spray venom, blinding the crab and eventually causing it to die. The ants then consume the meat, and the rich source of food allows the colony to expand, creating a vicious cycle.

Professor Lin said that once the ants form what is known as a super colony it can have a devastating impact on crab ecology.

Researchers from Melbourne’s La Trobe University working on Christmas Island found that super colonies of yellow crazy ants there dominated more than 2,500 hectares of forest, with a density of up to 1,000 ants per square meters in heavily infested areas.

The yellow crazy ant infestation on Christmas Island caused an estimated reduction of around 40% of the red crab population in the past 15 years, according to the La Trobe University research team.

For Orchid Island’s indigenous Tao people, the land crab forms part of their diet, and tradition and customs. Around April every year, the Tao celebrate a crab festival. The crab festival is a critical part of the flying fish season – flying fish being an important staple food of the Tao.

Lan An Cultural and Educational Foundation chief executive officer Maraos said that before the crab festival, only men are allowed to partake in catching flying fish. During the crab festival, Tao women catch land crabs to cook them for their male relatives to show appreciation for their hard work. In the part of the flying fish season after the crab festival, both sexes can partake in the flying fish harvest.

Maraos said that the Crab Festival is very important part of the flying fish season. It is the beginning of the second phase of the flying fish season. If the crabs decrease or disappear, it will impact the flying fish culture.

crab claws strung up outside a home on Orchid Island
Tao children string together crab claws and hang them outside their homes, showing the bravery and skills of their mother in catching live land crabs by hand. Picture: Lan An Cultural and Educational Foundation
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