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Food Science


Virgin births and not-so-vegan salads

by Arminda Downey-Mavromatis
July 5, 2019 | A version of this story appeared in Volume 97, Issue 27


A surprise in the anaconda exhibit

A woman with blue hair holds a small snake.
Credit: New England Aquarium
Sssssurprise: Biologist Tori Babson holds one of the two surviving babies.

Confusion turned to excitement at the New England Aquarium earlier this year when Anna, a female green anaconda housed only with other female anacondas, gave birth to 18 young.

“We were all pretty surprised. It’s not every day that you walk into an exhibit of four female anaconda to find a whole bunch of baby anacondas,” Tori Babson, a biologist at the New England Aquarium, tells Newscripts.

DNA testing confirmed the mechanism behind the bewildering birth: parthenogenesis, a type of asexual reproduction that’s common in invertebrates and plants but less frequently seen among snakes. Anna the anaconda needed a male about as much as she needed a bicycle. One of Anna’s egg cells joined to a second polar body, a typically unused by-product of egg creation. Unbeknownst to her keepers, she was pregnant with all female offspring.

Warren Booth, a biologist at the University of Tulsa, explains that there was a time when scientists believed that snakes had Z and W sex chromosomes, with females being ZW and males being ZZ. But the discovery of all-female parthenogenetic offspring changed that.

“We were able to show that boas and pythons actually have XX and XY sex chromosomes, with the female being XX, and that’s why she can only produce female parthenogens,” he tells Newscripts.

Booth began researching snake parthenogenesis accidentally. A snake collector and breeder contacted him to ask for a snake paternity test, as a female boa constrictor had produced offspring with unusual and valuable coloring. None of the four possible fathers matched the DNA of the offspring: the babies were all parthenogenetic.

“It was a totally fortuitous event: a paternity test and a snake,” he recalls.

Of the 18 anacondas born to Anna, only two are still alive. One is smaller than normal and has a facial deformity, but otherwise both are doing fine. The low survival rate is an unfortunate complication of parthenogenesis.


That’s not a crouton

A photo of a frog leaping out of a bowl of salad.
Credit: Shutterstock/C&EN
Amphibious assault: Watch out for frogs in your prepackaged salad.

Prepackaged salads are a convenient way to consume leafy greens. Sometimes, just sometimes, they come with an extra, er, surprise. An animal, usually an amphibian or reptile, has come with prepackaged salads in the US 40 times between 2003 and 2018, according to a recent study (Sci. Total Environ. 2019, DOI: 10.1016/j.scitotenv.2019.03.254).

Researchers from the University of Illinois at Urbana-Champaign tracked the phenomenon by collecting media reports of animals found in prepackaged salads. Daniel Hughes, a postdoc who worked on the study, says it was a way to gain context for wider research on nonlethal ways to keep frogs away from agricultural fields.

The results of the survey raise several questions about the way greens are farmed. The mechanization of farming makes harvesting leafy greens more efficient, but the process makes it trickier to detect a wayward toad. And while Hughes saw individual news reports blaming the organic nature of the produce for the critter contamination, there wasn’t evidence to support the assertion that organic produce was any more prone to these incidences than conventional produce.

“You have one field that just happened to be labeled organic, where they don’t treat it with pesticides. And the next field over is not organic and is treated with pesticides,” Hughes explains to Newscripts. “It’s not like there’s giant walls or anything like that.”

Though only 40 instances of salad surprises were found, Hughes is sure more are out there, reported on social media or directly to the companies. A reporting database would be helpful to researchers, who, with the benefit of a greater sample size, might be able to make better use of these data. Until then, wash your greens with care.

Arminda Downey-Mavromatis wrote this week’s column. Please send comments and suggestions to


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