Yellow Crazy Ants threaten native butterflies

Research conducted by undergraduate students and led by Dr Lori Lach found the formic acid-spraying pest is at least four times more likely than the native green tree ant to find and attack cruiser butterfly larvae.

 Dr Lach said both ant species will attack caterpillars, but the YCA’s sheer numbers meant caterpillars rarely escaped from areas the ants invaded. Up to 16 times more caterpillars were attacked in sites with YCA than in sites with green tree ants.

The voracious YCA has invaded about 800 hectares in the Far North, with about a third of the infested area being rainforest. An aggressive baiting program had forced YCA numbers down for the time being, but Dr Lach said scientists were wary of what the invasion could mean if treatments don’t continue.

“The rainforest is more complex than many habitats and may be more resilient, but we’re worried about a possible cascade of events. Decreases in key groups, such as pollinating butterflies, will likely have knock-on effects.”

In other habitats the ants have devastated wildlife – wiping out millions of red land crabs on Christmas Island, which helped transform the forest landscape and led to the death of some species.

“We might not be able to predict exactly what the effect will be,” said Dr Lach, “but we know it won’t be a good thing. The cruiser butterfly is a species with similar habits and habitat to many other native butterfly species.”

The ants spray formic acid in the eyes of their prey and there are reports of attacks on pets and people. They are known to actively protect sugar cane pests in order to milk them for honeydew.

Dr Lach said that the current funding to the Wet Tropics Management Authority would not be enough to eradicate the ants from the area. The state and federal governments are considering a proposal for $5.06 million per year for an initial three years with provision for additional funding for another seven after that.

 “It seems like a lot of money, but in the context of how precious the Wet Tropics World Heritage Area is and how many animals and plants are absolutely unique to it, it’s not much at all,” she said.

Dr Lach said the Wet Tropics World Heritage Area is home to 58% of Australia’s 400 butterfly species.