Australasian Science: Australia's authority on science since 1938

Crazy Ants Beating Butterflies

James Cook University scientists have discovered that the invasive yellow crazy ant is an extremely efficient killer of native butterfly caterpillars.

Dr Lori Lach found that 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.

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

The voracious yellow crazy ant has invaded about 800 ha in Far North Queensland, with about one-third of the infested area being rainforest. An aggressive baiting program had forced yellow crazy ant numbers down for the time being, but 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.”

The ants have already wiped 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,” Lach said, “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.

Lach said that current funding to the Wet Tropics Management Authority would not be enough to eradicate the ants from the area, which is home to 58% of Australia’s 400 butterfly species.