Paul Abram, a PhD student at the University of Montreal in the biological sciences department, had his eureka moment two years ago, when he noticed a newspaper lining the bottom of a cage of the bugs.
There was a crossword puzzle covered in eggs.
"I noticed there was a tendency for darker eggs to be laid on the darker parts of the crossword puzzle and lighter eggs on the lighter parts," Abram said. "So that made me wonder, can the stink bugs actually control the colour of the eggs that they're laying?"
The species he and his colleagues studied, Podisus maculiventris, is found in fields and backyard gardens across North America. In nature, darker eggs are often found on the darker side of leaves, and lighter eggs on the underside.
Abram has raised several species in his laboratory and noticed there's a huge variation in the colour of eggs, all the way from pale yellow to darkish black.
Now, he believes he knows why.
"We think it's the first example of an animal that can selectively control the colouration of its eggs, and in the process of making this discovery, we also found that the pigment that they use actually is something that is probably unknown."
Most dark pigmentation in nature is attributable to melanin — for example, hair colour and skin colour in humans. But Abram found the pigment that's responsible for the stink bug's egg colour, that protects again ultraviolet radiation from the sun, is not melanin.
"It's potentially a new compound. So it's opening a new line of research that we may have discovered another chemical compound," said Abram, adding that the discovery has opened up more questions than it answered.
"This is what often happens. Every time we get an answer, we get five more questions."
Now Abram and his fellow researchers want to know what the new pigment is.
"Does it exist in other species of animals. What's the chemical structure?"
Abram and his colleagues reported their findings in the journal, Current Biology.