Myrmecia croslandi: The Ant With a Single Chromosome

Nov 3

2 min read

Myrmecia croslandi looks like an ordinary jack jumper, but it holds a world record that has nothing to do with size or venom. It has the lowest number of chromosomes possible for any animal. On top of that, it has become a star of research on how ants learn their way home.

Myrmecia croslandi bull ant — Myrmecia croslandi.

A jack jumper of its own

Myrmecia croslandi is a jumping bull ant, so it can be called a jack jumper, just like its close relative Myrmecia pilosula. For a long time it was seen as part of that species. It was described as a separate species in 1991 by the Australian myrmecologist Robert Taylor. It lives in eastern Australia, in New South Wales and Queensland.

One chromosome

Most animals have dozens of chromosomes; humans have 46. Males of Myrmecia croslandi have just a single chromosome, and females have one pair. That is the simplest set of chromosomes possible for any animal. This unique feature helped show that Myrmecia croslandi is a separate species. It works because, in ants, males develop from unfertilised eggs and therefore have only half the chromosomes of females.

Learning walks

Myrmecia croslandi is also famous among researchers who study insect navigation. Before a young worker goes out to forage for the first time, it makes a few learning walks around the nest. It walks slowly in arcs, turning its head back and forth between the nest and the opposite direction. A 2018 study found that young workers make between two and seven of these walks, spread over up to four days, each time exploring a different direction. That way, they learn what the nest surroundings look like from many points of view.

Finding the way back

Like other bull ants, Myrmecia croslandi forages alone and does not use scent trails. It finds its way using the shapes of trees and other features of the landscape. Read more in how bull ants find their way.