Written by Cara Giaimo
Here’s a pop quiz for you. Tom is taller than Dick. Dick is taller than Harry. Who’s taller, Harry or Tom?
If you said Tom, congratulations! You just demonstrated what’s called “transitive inference” — the ability to compare things indirectly, based on previous juxtapositions. But before you pat yourself on the back too much, you should know that this skill was recently demonstrated by another creature:the humble paper wasp that might be living in your backyard right now.
In the summer of 2017, researchers at the University of Michigan put two species of paper wasps through a transitive inference test. A statistically significant portion of the time, the wasps passed. Other animals — including rats, geese and cichlid fish — have also exhibited this capacity. But this study, which was published Tuesday in Biology Letters, is the first to successfully showcase it in an invertebrate (honeybees failed a similar test in 2004).
Paper wasps are found on every continent except Antarctica. You might be near some right now. “They tend to nest in the eaves of houses, or inside barbecue grills,” said Elizabeth Tibbetts, the study’s lead author.
In a previous study, Tibbetts showed that individual female wasps can identify one another by their distinct facial patterns, which resemble Rorschach ink blots. “When two wasps meet, they learn, ‘Oh, that’s what Suzy looks like,’” she said. “And the next time they meet, they remember who Suzy is.”
In the spring, the females spend a lot of time brawling, getting in each other’s faces and trading slaps with their appendages. These matchups look like schoolyard tussles. “Some wasps will be fighting; some wasps will be watching the fights,” Tibbetts said. “It’s a very exciting time.” The wasps remember the winners and losers, and use them to establish a social hierarchy: the strongest reproduce, while the weaker ones do all the work.
Tibbetts and her colleagues wanted to see whether the wasps could take this a step further. Say a particular paper wasp beat Suzy, and then was ringside a few days later when Suzy walloped Jane. Could that wasp figure out that she’d probably best Jane, too?
Such knowledge would require transitive inference. So the team turned to what’s called a “five-element training procedure,” now a standard way to test this skill in animals. They put the wasps in a series of bi-colored chambers. If they moved toward the wrong color, they got a mild electric shock. In this way, “you train them that blue is better than green, and once they learn that, you train them that green is better than purple,” said Tibbetts. They did this for four pairs of five colors.
After the wasps had been trained, they were put in a new chamber. This one had colors they were familiar with from the training, but hadn’t been paired up before. About 67% of the time, the wasps successfully chose the “better” color — the one less likely to shock them.
“They are organizing all those pairs into a linear hierarchy in their head,” Tibbetts said. Next, she plans to study how the wasps actually use this ability during social interactions.
Colin Allen, a cognitive philosopher at the University of Pittsburgh, cautions against over-interpreting the study, saying the simplicity of the test makes it “hard to judge what processes are operating in these wasps.” But he calls it “an important reminder” that just because bees can’t do something, doesn’t necessarily mean that no insects can.
It fits well with another of the study’s lessons: Just because humans can do something, doesn’t necessarily mean that all insects can’t.