Bed bugs (Cimex lectularius) like to hide in cracks and crevices (known as their "harborage") and they spend most of their time cuddled up in the best nooks they can find. As bed bugs become increasingly resistant to insecticides, scientists are more and more interested in figuring out what makes a good harborage — and how humans can ruin them.
Lots of insects use color as a behavioral cue, and color is a cheap thing to change when designing a new kind of trap. So researchers at the University of Florida and Union College decided to see if bed bugs showed any color preferences. Previous studies have shown that bed bugs can't distinguish color very well in the dark — which is when they do most of their moving and feeding — but the researchers wanted to see whether color might be important when bed bugs had light shone on them, which usually prompts a frenzied move toward hiding places.
"It was speculated that a bed bug would go to any harborage in an attempt to hide," the researchers wrote in the study. "However, these color experiments show that bed bugs do not hide in just any harborage; rather, they will select a harborage based on its color when moving in the light."
They placed bed bugs in petri dishes with different color choices; little tents of colored material. Each bug got 10 minutes to pick a hiding spot, then its choice was recorded. The researchers shuffled the color choices around to be sure their picks weren't based on location within the dish, and they tested bed bugs of different age, sex and feeding status to check for differences in color preference. They also did longer experiments with females who were about to lay eggs to see if they had a favorite shade under which to leave their brood.
Bed bugs that were hungry cared less about color in general, and the different sexes had different colors that they favored over white. But across the board, the bed bugs showed a significant preference for red and black.
"We originally thought the bed bugs might prefer red because blood is red and that's what they feed on," study co-author Corraine McNeill of Union College said in a statement. But the researchers found that the bed bugs seemed to like black just as much — and that they cared less about what color they scurried to when they were looking for a meal — which suggested that something else might be going on.
Yellow was basically as unpopular as white with all of the bed bugs tested, with green following close behind. That may be because the bugs read yellow as bright, making them want to hide from it as if it's a light. Conversely, they might see red and black as being dark, and therefore hidden and safe. It could also be that red and black surfaces look more like piles of bed bugs, while yellow and white surfaces show nervous critters that they're all alone.
The researchers only tested the egg-laying preferences of 10 bed bugs — which isn't enough to draw any strong conclusions from — but for what it's worth, the bugs they studied didn't seem interested in laying eggs under yellow or green harborage.
"I always joke with people, 'Make sure you get yellow sheets!'" McNeill said in a statement. "But to be very honest, I think that would be stretching the results a little too much."
After all, bed bugs are often already settled into their hiding places when you turn your bedroom lights on — and when they scurry around in the dark, they don't give a hoot whether your sheets are black as night or yellow as the sun. But these color preferences could still be useful in designing traps: "The point isn't to use the color traps in isolation, but to use color preference as something in your toolkit to be paired with other things such as pheromones or carbon dioxide to potentially increase the number of bed bugs in a trap," McNeill explained.
Then again, bed bugs tend to make people pretty desperate. So if you're in the throes of a debilitating infestation, maybe it's worth giving bright yellow sheets a go. We won't judge.