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Cabezonication / iStock

Where humans go, ants will follow. A new study of invasive ant species uses historical records to chart their spread across the world, reports Smithsonian Magazine. The researchers found that ants moved in waves: the first came after the industrial revolution and the second followed World War II and continues today. Species like painful fire ants have crossed oceans and continents to colonize new lands.

"Humans have left a fingerprint on the distribution of these species," Cléo Bertelsmeier, one of the study authors, tells Smithsonian.

Why it matters: Invasive ants can pose major threats to local ecosystems, wrecking insect biodiversity and even killing ground-dwelling animals. Scientists hope that by understanding what helped ants spread in the past, they can prevent future invasions.

How they did it: Bertelsmeier used public databases to identify 241 invasive ant species, and examined what life-history traits they had in common. She was able to find enough historical data to chart the spread of 36 of those species.

The researchers also identified factors that made some ants more likely to gain a foothold in their new environment. Smaller ant species with multiple queens were tended to be successful, as were ants that thrived in areas that were disturbed by humans.

Go deeper

Netflix tops 200 million global subscribers

Illustration: Rebecca Zisser/Axios

Netflix said that it added another 8.5 million global subscribers last quarter, bringing its total number of paid subscribers globally to more than 200 million.

The big picture: Positive fourth-quarter results show Netflix's resiliency, despite increased competition and pandemic-related production headwinds.

Janet Yellen plays down debt, tax hike concerns in confirmation hearing

Treasury Secretary nominee Janet Yellen at an event in December. Photo: Alex Wong via Getty Images

Janet Yellen, Biden's pick to lead the Treasury Department, pushed back against two key concerns from Republican senators at her confirmation hearing on Tuesday: the country's debt and the incoming administration's plans to eventually raise taxes.

Driving the news: Yellen — who's expected to win confirmation — said spending big now will prevent the U.S. from having to dig out of a deeper hole later. She also said the Biden administration's priority right now is coronavirus relief, not raising taxes.

Trump gives farewell address: "We did what we came here to do"

Photo: Mandel Ngan/AFP via Getty Images

President Trump gave a farewell video address on Tuesday, saying that his administration "did what we came here to do — and so much more."

Why it matters, via Axios' Alayna Treene: The address is very different from the Trump we've seen in his final weeks as president — one who has refused to accept his loss, who peddled conspiracy theories that fueled the attack on the Capitol, and who is boycotting his successor's inauguration.