Supercolonies of ants are wreaking havoc on Christmas Island!

The Yellow Crazy Ant is crazy vicious!

In our previous newsletter, we learnt about the birds of Christmas Island, an island made out of coral reefs located just over 1,000km away from Singapore.

While doing research on the Abbott’s Booby (a type of seabird that has the wonderful distinction of being named after the boobs - not really, they were named for the fact that they were ‘bobo’ aka stupid) I learnt about a huge threat to the existing Booby population: yellow crazy ants!

Image credit: BirdLife Photography. An Abbott’s Booby, a type of bird that breeds only on the Christmas Islands. Their existence is threatened by supercolonies of Yellow Crazy Ants.

Like their name suggests, they’re crazy!!

The Yellow Crazy Ant

Also known as the long-legged ant or Maldive ant, the yellow crazy ant is a species that in not only named for their yellow colour, but also for their crazy behaviour. They are thought to be native to West Africa or Asia but have been accidentally introduced to numerous places in the world's tropics, where they thrive.

Image credit: The Wild Martin. A close-up photo of the Yellow Crazy Ant.

And sadly, where they wreak havoc on local ecosystems!

There are over 12,000 species of ant, most of which are black, brown, or red in color. Ants are found almost everywhere on the planet. The only areas that don't boast populations of ants are Antarctica, Greenland, Iceland, and some island nations.

Most species of ants live in soil, leaf litter, or decaying plants, but in the cities, they can be found in human homes or any place near food - especially sugar!

There are an estimated 20 quadrillion ants on Earth. This figure is said to actually be conservative and there may be even more ants in the world! Ants outnumber humans at least 2.5 million to 1.

Image credit: Peter Yeeles. While the exact origin of yellow crazy ants remains unclear, their current distribution extends through the tropical islands of the Indian and Pacific Oceans, including Papua New Guinea, Mauritius and South East Asia where they are a major pest. This broad distribution is undeniably linked to human movement activities such as cargo ships and trade.

Why are they called ‘crazy’?

The yellow crazy ant is known for their extremely erratic and unpredictable movements when disturbed. They have long legs and antennae, so I guess they really do look quite crazy when they are waving all their spindly bits around.

The yellow crazy ant is actually on a list of "one hundred of the world's worst invasive species" formulated by the International Union for Conservation of Nature (IUCN).

They have invaded ecosystems from Hawaii to the Seychelles, and formed supercolonies on Christmas Island - where, as I mentioned above, they are ruining the homes of the seabirds that live there.

How does that work?

Like several other invasive species of ants, the yellow crazy ant is what is known as a "tramp ant", a species that easily becomes established and dominant in new habitat due to traits such as aggression toward other ant species, and large colony size.

When they touchdown on a new base, they’ll violently and aggressively chase out out the other inhabitants while establishing their own rule.

And, like Wikipedia so gently advises me, this ant is not to be confused with the longhorn crazy ant or the Rasberry crazy ant. (Not raspberry like the fruit! Rasberry, named after a person.) I honestly had no idea there were so many crazy ants in the world, wtf.

Yellow crazy ants, and other ‘tramp ants’, have the diet of a scavenging predator - they will consumes a wide variety of foods, including grains, seeds and other insects. But they’ll also take in decaying matter such as animal corpses.

These ants have been reported to attack and dismember invertebrates such as spiders, land crabs, earthworms and other insects!

Image credit: Wet Tropics. Rather than establishing several competitive nests with individual queens (as majority of other ant species do), yellow crazy ants establish supercolonies—large interconnected nests containing multiple queens. Nests have been found containing hundreds of queens and many magnitudes more of workers. By cooperating, yellow crazy ants can successfully outnumber and displace other species, thereby dominating food and nesting resources.

On the Christmas Island, an invasion of the yellow crazy ant poses continued risk for the Abbott’s Booby population.

How can tiny little ants threaten large birds?

The main reason is that supercolonies of the yellow crazy ant ruin the land itself, which in turn, hurts the livelihoods of the birds. The ants disrupt the ecosystem and limit food supply by killing the red crabs and insects that live on this island, as well as the damaging the trees where the boobies nest.

Image credit: Phys.org. A group of Christmas Island Red Crabs scurry towards the sea. The mass migration of 45 million crustaceans begins at the start of the wet season in October or November each year.

Adult crabs leave their burrows in the jungle and hurry to the beach for a dip in the ocean to replenish body salts.

Although crazy ants do not bite or sting, they spray formic acid as a defense mechanism and to subdue their prey - namely, the land crabs of Christmas Island.

The high levels of formic acid at can blind and eventually kill the land crabs due to dehydration and exhaustion. As the dead crabs decay, the protein becomes available to the ants… Creepy but pretty effective! For the ants, anyway.

The ant supercolonies have killed up to 20 million of the Christmas Island land crabs, which are vital to Christmas Island's biodiversity. These crabs are a keystone species in the forest ecology: they dig burrows, turn over the soil, and fertilise it with their droppings. Without the crabs, the whole island is affected!

Wait - what are supercolonies?

Yeah! As if the ants themselves weren’t bad enough, there are supercolonies of them.

Like the original European pilgrims in the United States of America that killed off the Native Americans, supercolonies can overwhelm the natural inhabitants on an island.

All ant species form colonies consistent of at least one egg-laying ‘queen’ ant. However, supercolonies are huge ant colonies that can feature several queens! These supercolonies can spread over large areas, in some cases thousands and thousands of square kilometers.

Ant supercolonies spread farther and cause more damage than single colonies, and they pose the single greatest known threat to the Christmas Island's biodiversity.

Back to the birds on Christmas Island…

The Christmas Island National Park houses all known Abbott's booby nest sites. This national park covers 60% of the island!

Although yellow crazy ant colonies are threatening these areas, there have been tons of control measures set in place. These measures includes surveying, insecticide, and baiting.

It’s impossible to fully control these supercolonies (once you control a section of it, the ants will simply breed again and overtake that same section). But the Environment Australia Abbott's Booby Recovery Plan aims to regenerate forests and help prevent further decline in the species. Even though the yellow crazy ants pose a continued risk for the booby population, the wonderful people of the island have been working hard to control their numbers - today, there is 95% reduction of the ants’ range!

Image credit: Western Australia Museum. An Abbott’s Booby successfully nests on a tree in Christmas Island.

Let’s hope the humans on Christmas Island succeed, and the ants stop threatening the land on which the Abbott’s Booby nests on!

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