A worker yellow crazy ant. Hugo Darras photo

Researchers just discovered a method of animal reproduction previously unknown to science, reporting that a biological law is being “broken” by a species of ant.

The yellow crazy ant, according to a paper published Thursday in the journal Science, lives up to its name. The acid-spraying insect has a bizarre form of reproduction unseen until now in the animal kingdom, one that may have allowed it to become one of the world’s worst invasive species, devastating many of the delicate ecosystems it encounters.

“The discovery is quite extraordinary,” said Denis Fournier, an ant biologist at the Université libre de Bruxelles who was not involved in the research. Pinpointing the ant’s novel form of reproduction, he added, offers “yet another glimpse of what nature is capable of inventing.”

A quick refresher from your sex-ed class: Normally, an embryo – in everything from humans down to the simplest multicellular animal – develops after a sperm fertilizes an egg. That single, fused cell divides to form an organism made up of genetically identical cells. Pluck nearly any cell from your body, and you should see the same DNA as you would in any other cell.

But yellow crazy ants – or at least, the male ones – are different.

Rather than fusing together, the genetic material from a queen’s egg and her mate’s sperm do not mix when forming a new male. Instead, the female and male ant both contribute DNA-laden nuclei, which begin replicating separately over and over again. These form into cells, which then become bound up in an embryo.


As a result, the bodies of male yellow crazy ants are not composed of cells containing the same set of DNA. The male ants are instead made up of two cell lines each with its own distinct genetic lineages – one from the queen and the other from her mate. The species’ queens and female workers, by contrast, form from a regular sperm-egg combination.

“It’s exciting to be at the frontier of knowledge,” said Hugo Darras, an evolutionary biologist at the University of Mainz in Germany and the paper’s lead author, in a Zoom interview.

Having studied plenty of other species, Darras added, “This is by far the most bizarre system I’ve ever worked with.”

Two male yellow crazy ants. Hugo Darras photo

A male yellow crazy ant represents what scientists call a chimera, or a single animal with two sets of genetically distinct cells. The name comes from a Greek mythological creature that is part lion, part goat and part serpent.

Scientists have found a handful of chimeras in nature, both in humans and other species, sometimes resulting in people or creatures with two different colored eyes. But most chimerism usually stems from rare developmental incidents, such as when one embryo absorbs another in the womb.

Scientists have known for a while that the sex life of ants is strange. Queens of some species clone themselves. Other kinds of ants have no males at all. And yet some ant species are thought to have four sexes.


Benjamin Oldroyd, an emeritus professor of behavioral genetics at the University of Sydney who was not involved in the paper, said he has tried to write out a list of reproductive modes of ants and related species, “both real and imagined.”

“But every time I wrote out such a list, it turned out that fact is stranger than fiction,” he said. “I never imagined a species in which males would be a mixture of cells of two lineages, and that one lineage would be used for making sperm. I can only describe this ‘crazy ant sex’ as beyond my imagination.”

Yet even in the crazy world of ants, the yellow crazy ant stood out before this discovery.

The species ranks as one of the worst insect invaders, marching through island ecosystems from Hawaii to Zanzibar. Supercolonies of these frenetic insects spray an acid to subdue prey – perhaps most notably, decimating red land crabs on Christmas Island in the Indian Ocean. The International Union for Conservation of Nature listed the crazy ants among the “100 of the World’s Worst Invasive Alien Species.”

The yellow crazy ant’s peculiar way of reproducing may give it an edge as an invader. By carrying two separate genetic linages, the males may have a reduced chance of inbreeding, even if just a few arrive on an island.

But Darras cautioned a lot more work needs to be done to explore these questions. “At the moment, it’s speculative,” Darras said. This yellow crazy ant study, he added, was about 15 years in the making.


“I imagine that the authors still have a lot to discover and tell us about the yellow crazy ant,” Fournier said.

Whatever the reason the ant evolved this unusual mode of reproduction, Darras and his team wrote the ant is breaking a “fundamental law of biological inheritance” with a “reproductive mode unknown to science” until now.

Darras noted that the vast majority of ants go unstudied. “I would not be surprised if we discover something similar in another species.”

Daniel Kronauer, a professor at Rockefeller University, noted there are few ironclad rules in biology. “Fundamental laws are something for physics. Biology is more like a collection of exceptions,” he said.

But he added, “This is one very interesting exception.”

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