Zero is an abstract concept. It's one which humans understand but most animals, save for dolphins, parrots and primates, don't. Children don't usually get a handle on it until kindergarten. Apparently bees get it though.
To find out if bees could understand the notion of zero, a team of scientists put out sheets of paper that had different numbers of objects printed on them. They then put sugar on the paper with the fewest number of objects. Once done enough times, the bees were trained fly to the sheet with fewer objects, even when the sugar was gone.
Then they put out blank pieces of paper next to the printed paper. Amazingly, the bees flew to the blank paper. Not only that, when the experiment was repeated they chose the blank paper 60 to 70 percent of the time, too high to be a matter of chance. To understand how impressive this really is we need to look back at the history of the number zero.
The Sumerians seem to be the first culture to understand zero. Interestingly, they didn't have a numeral but instead a symbol, a slanted double wedge, that indicated an absence of a number when placed between two others. Records showing this symbol date back around 5,000 years.
To put that into perspective, modern humans made their appearance at least 130,000 years ago. That leaves a pretty good stretch of time where we didn't have a way to communicate zero and perhaps couldn't wrap our head around it at all. What's more, some ancient cultures that came after the Sumerians had numerals for zero while others didn't, indicating that the concept is taught and not innate. However, these findings indicate that the ability to understand zero may be more widespread amongst animals than we previously thought.
To read more check out the article over at Vox. https://www.vox.com/science-and-health/2018/6/7/17437640/bees-zero-math-humans-science