Yellow Crazy Ant

Fascinating facts about the Yellow Crazy Ant

• A single supercolony on Johnston Atoll once covered almost a quarter of the island, packing up to 1,000 queens into a 6-metre-wide (20-ft) plot – a living metropolis that threatened the island’s birds before eradication.
• On Christmas Island the ants have displaced an estimated 15–20 million red crabs, wiping out their burrows and turning a keystone species into a food source that fuels further ant growth.
• In the Seychelles a colony can spread up to 400 m (1,300 ft) in a year, but on Christmas Island surveys recorded an average advance of 3 m (9.8 ft) per day – enough to add roughly 1 km (0.6 mi) each year.
• When researchers removed the ants from an area, scale-insect numbers fell 67 % in just 11 weeks and disappeared entirely after 12 months, showing how tightly the ants’ honey-dew diet is linked to those plant pests.
• A 2012 Queensland cost-benefit analysis warned that unchecked ant spread could cost Australia over A$3 billion, a figure that excludes the likely loss of biodiversity in vulnerable rainforests.

At a glance

About the Yellow Crazy Ant

The yellow crazy ant (Anoplolepis gracilipes) is a strikingly large, yellow-to-orange insect with unusually long legs, oversized eyes and antennae that extend far beyond its head. Its slender body and the presence of an acidopore set it apart from look-alikes such as Leptomyrmex and Oecophylla, while a compact petiole distinguishes it from the arboreal weaver ants. Native to the moist tropical lowlands of Southeast Asia, this tramp ant has hitchhiked across the globe, establishing dense populations throughout the Pacific, Indian Ocean islands and parts of northern Australia, the Caribbean and the Galápagos. In its new homes, it forms sprawling supercolonies that can stretch a kilometre a year on Christmas Island, moving up to 400 m annually in the Seychelles, and it spreads primarily by budding, mated queens and workers abandoning the nest to start new ones, though occasional winged females can take to the air. A true scavenging predator, A. gracilipes devours grains, seeds, dead vertebrates and a bewildering array of invertebrates, from isopods to land crabs. It also farms scale insects, protecting them in exchange for honeydew, a relationship so tight that removing the ants caused scale densities to plunge 67 % in just eleven weeks and disappear within a year. A surprising twist emerged in 2023: males are obligate chimeras, developing from fertilized eggs that bypass normal nuclear fusion, yielding individuals with mixed W- and R-genome cell lines, a first in animal biology. This odd reproductive quirk may help the species maintain its aggressive edge as it overruns ecosystems.

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