Crazy Yellow Ant

Image source

This little guy means big problems. The crazy yellow ant shows, for good or ill, the impressive power of cooperation. At less than half a centimetre long they aren't even large for ants, though their legs and antennae are unusually long. The 'crazy' part of their name comes from their madcap movements which become frenetic and frantic when they are disturbed.

There's something else they do when they're disturbed. While they can't sting, they can spray formic acid in defence. This stuff can actually cause blindness if it gets into the eyes so if you get it on your hands it's best to wash them immediately.

These are ants, so they obviously nest in colonies. I wouldn't like to stumble and tumble into a nest of these acid spewing terrors so the question arises: where are these little beasts from?


Here's the thing, yellow crazy ants are found all over the place, to the extent that no-one can be sure where they actually originate from. These days they can be found on Caribbean islands, Pacific islands and various islands in the Indian Ocean. They can infest plantations and aren't particularly fussy about where they nest, meaning that colonies of various sizes can hitch a ride on trucks and boats, ending up in far flung islands like Hawaii, Mauritius and the Galapagos.

It is on Christmas Island however, that the full force of the crazy yellow ant can be felt.

Christmas Island is a small island in the Indian Ocean, just south of Indonesia. It is famed for its array of animals and plants found nowhere else on Earth, its sea-bird nest sites and its land crabs. The fact that it didn't become inhabited until the late 19th century probably helped there. But then it became inhabited.

Yellow crazy ants were introduced between 1915 and 1934 and gradually began to flourish. They pose several problems for the native land crabs.

For one, yellow crazy ants eat just about anything, from seeds and honeydew to decaying meat and living meat. They are both scavengers and predators of snails, insects, worms and near enough everything else, including crabs.

Unfortunately, land crabs and yellow crazy ants also share space on the forest floor. For a while at least. Land crabs simply can't fight against huge numbers of tiny acid spraying ants, particularly if that acid has blinded them. If the crab has stumbled into an ants nest, the ants simply won't stop until the threat is gone. Or dead.

To add insult to injury (or death), yellow crazy ants will also take over departed crab burrows to grow their colonies.

And what happens when a yellow crazy colony meets another yellow crazy colony? Many species of ant will fight with rival colonies, helping to control their numbers. Yellow crazy ants on the other hand, can form supercolonies, where various colonies cooperate and have no aggression toward each other even though they all have different queens. This leads to an extraordinary number of ants. The highest density of foraging ants ever discovered in fact, 2,254 foraging ants per metre squared, spewing forth from nests housing up to 300 queens. They spread like wildfire; by September 2002, they infested 28% of the 10,000 hectares of rainforest on Christmas Island.

Where these ants are, the Christmas Island red crab is not. Some 20 million red crabs are said to have been killed by these ants. Since the red crabs are the main consumer of seeds, seedlings and leaf litter on the island, their absence has the potential to transform the rainforest. The yellow crazy ants also get their honeydew from aphids and scale insects, providing the foragers with much needed sugar energy. It seems that a lack of scale insects actually limits the ant population growth, and without defence from the ants, scale insect numbers plummet. On the other hand, with too many scale insects sucking sap from plants and trees they can promote the growth of mould, which can cause dieback and even the death of trees. Sometimes it takes a tiny island to really see the balance of ecosystems.

And so war is declared. On Christmas Island they have found success with a poison called Fipronil. It doesn't affect other creatures on the island and is slow acting enough for ants to take it back to their nest and eventually, the queen herself. The yellow crazy ant has also been eradicated in parts of north-eastern Australia, but the battle continues. Costly and time consuming, it is a terrible lesson in just how delicate the living world can be and the incredible, long term work required to rectify problems.