Yellow ants driving conservationists crazy

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The yellow crazy ant native to Southeast Asia is listed as one of the 100 worst invasive species in the world. It has invaded islands such as Christmas Island, Hawaii, Tuvalu, Tokelau, Kiribati, several islands in the Pacific Ocean, as well as the Seychelles.

Conservationists fear that if yellow crazy ants go unchecked, delicate Seychelles’ ecosystems will be lost similar to Christmas Island. There, yellow crazy ants formed one of the largest known super colonies and wiped out a third of the island’s endemic red crabs, prompting scientists to come up with the term ‘invasional meltdown.’

“Crazy ants get their reputation from the impact they have on other species, ecosystems, people and agriculture,” says Lorraine Cook, science officer at the Seychelles Island Foundation (SIF). In order to prevent events similar to those of Christmas Island from happening on Seychelles, SIF is working hard to remove invasive yellow crazy ants from the ecosystem.

How do yellow crazy ants operate?

Photo: Seychelles Island Foundation

The yellow crazy ants’ whole way of life makes them successful invaders. “Yellow crazy ants require sugary liquids and solid protein to function,” says Cook. In Seychelles, they get their sugar requirements from fruit, nectar and honeydew. Their protein comes from scavenging or hunting invertebrates, lizards, slugs, snails and snakes. The ants use formic acid to subdue their prey.

To make matters worse, yellow crazy ants form mutualistic relationships with pests such as aphids and scale insects. Honeydew, one of their food sources, is a by-product produced by scale insects. In order to get more food, the yellow crazy ants protect the scale insects from predators. The food is then taken back to the colony.  “It’s important to understand that these ants operate 24 hours a day, all year round, attacking and killing everything in their path,” says Cook.

Yellow crazy ants live in large interconnected nests containing multiple queens and a couple of males. The majority of the colony consists of female worker ants that do all the food collecting. Yellow crazy ant colonies do display inter-colony aggression. The ants can cooperate and form one massive super colony, explains Cook. So far, no super colony has been recorded in Seychelles.

The impact yellow crazy ants have on endemic wildlife in Seychelles

Coco de mer palm. Photo: Seychelles Island Foundation

Thus far, the alien ant has invaded a UNESCO World Heritage Site, Vallée de Mai on Praslin Island in Seychelles. Vallée de Mai is home to a large population of coco de mer (Lodoicea maldivica) palm trees that only occur on Praslin and Curieuse islands. The coco de mer plays an important role in the lifecycle of many amphibians, geckos, skinks and birds that are found nowhere else in the world.

The giant bronze gecko. Photo: Seychelles Island Foundation

The effects of the ants are already being felt. “The ants are causing the decline of many animal species found only in the Vallée de Mai,” explains Cook. “In the unique coco de mer forest ecosystem, species are interconnected and rely on each other and create food webs.”

The coco de mer micro-ecosystem

The white slug, coco de mer snail, giant bronze gecko and black parrot are dependent on the coco de mer for survival. “The coco de mer snail is commonly seen on coco de mer,” says Cook. “The giant bronze gecko, the largest living gecko, only occurs in mature coco de mer forests.” Bronze geckos are believed to play an important role in pollen dispersal of the palm. The white slug has a symbiotic relationship with the palm and is only found on coco de mer’s hanging flowers. Black parrots create nesting cavities in the trunk and also depend on the fruits of all endemic palms.  “A decrease in any of these species could threaten the natural functioning of this ecosystem,” says Cook.

Seychelles black parrot. Photo: Seychelles Island Foundation

How SIF is working to eradicate yellow crazy ants

“Controlling the yellow crazy ants will require the use of a pesticide designed specifically for ants,” says Cook. The pesticide has been designed to be attractive to yellow crazy ants to prevent the death of non-targeted species. Small granules are scattered throughout the forest, the worker ants take the granules back to the nest thinking it is food. Once ingested the pesticide kills the queens and all developing larvae, thus destroying the nest.

Photo: Seychelles Island Foundation

How did yellow crazy ants get to arrive in Seychelles?

There are theories as to how the ants got to the island in the first place. “Yellow crazy ants are associated with people so can easily spread to new territories,” says Cook. It is believed that a suitcase packed with money (and ants) was sent from Mauritius to Maldive Village in Mahé in 1962.  The ants were then recorded on Praslin Island in 1975. It is believed they were brought over from Mahé in building material.

What happened on Christmas Island?

Christmas Island used to be home to 30-40 million endemic red crabs that were reduced to a third of their original numbers by ant activities. The red crab is considered a keystone species playing an important role in forest ecosystem function.

In addition to the red crabs dying off, the ants formed a symbiotic relationship with the introduced yellow lac scale insect, an herbivorous plant pest. The yellow crazy ants basically farmed the yellow lac scale insect, causing the rainforest canopy to die. “The combination of understory growth and canopy dieback changed the structure of the forest,” explains Cook. “This, in turn, had an impact on birds, lizards and other endemic animals.”

White slug found in the coco de mer palms. Photo: Seychelles Island Foundation

Written by: Georgina Lockwood

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