The Invasion of Yellow Crazy Ants

As one of the world’s top 100 worst invasive species (Lowe et al., 2000), the yellow crazy ants (Anoplolepis gracilipes) have now invaded Singapore! This species of ants are notorious of forming multi-queen supercolonies and invading large areas, which is one of the leading factors for its disastrous impact (Abbott, 2006). However, not many of us actually know about this particular “invasion”. In a quick survey around NUS, these ants are found in high densities at the patch of adinandra belukar secondary forest just behind NUH!

A close up picture of a yellow crazy ant.

A close up picture of a yellow crazy ant.

The yellow crazy ants got their name from their pale yellow colour and their frenetic or “crazy” movement when disturbed. Their extremely long legs allow them to move rapidly, which may give them an advantage over other ants when foraging the leaf litter for food. They are rather aggressive and sometimes also spray formic acid into other competing ants. Luckily, these ants does not seem to bite humans.

It’s hard not to wonder how creatures this small a size can actually cause a significant impact. However, this species of ants received worldwide attention for its devastating impact on endemic birds of Seychelles (Hill et al., 2003) and the red land crabs of Christmas Island (Abbott, 2006). In a recent study, these ants have shown high degree of exploitative and interference competition, and have successfully establish several colonies in Kent Ridge Forest and Bukit Timah Nature Reserve (Cedric et al., unpublished data). It is really hard to imagine what will happen if the population of these ants suddenly explodes. And for the current time being, the invasion progress of the yellow crazy ants have to be minitored.


Abbott K.L. (2006). Spatial dynamics of supercolonies of the invasive yellow crazy ant, Anoplolepis gracilipes, on Christmas Island, Indian Ocean. Diversity and Distributions. Vol. 12. pp.101-110.

Cedric K.W.T., Teh H.Y., Lee G., Corlett R.T. (unpublished data). Invasion of the Yellow Crazy Ant in Singapore.

Hill M., Holm K., Vel T., Shah N.J., Matyot P. (2003). Impact of the introduced yellow crazy ant Anoplolepis gracilipes on Bird Island, Seychelles. Biodiversity and Conservation. Vol. 12.  pp.1969-1984.

Lowe S., Browne M., Boudjelas S., De Poorter M. (2000). 100 of the world’s worst invasive alien species. Invasive Species Specialist Group.