Buzz
Predatory birds, like humans, are cautious around black widows. Recent research reveals that birds recognize and avoid these spiders due to their vivid red markings. In contrast, the spiders' prey struggles to detect these warning signs, remaining oblivious to the danger. The study's results were published last week in the journal Behavioral Ecology.
Black widows occupy a unique space in human culture. The female spider's deadly venom and iconic red hourglass markings have influenced musicians, comic book artists, and video game developers. The study's authors leveraged this cultural fascination in their research.
“Video game developers often include black widows in their games because they evoke fear,” lead author Nicholas Brandley explained in a press release. Brandley and his team purchased a digital model of a black widow (Latrodectus mactans) from a game developer. They modified the code for 3D printing, creating lifelike black widow replicas in the lab. Half of the eight models were painted entirely black, while the other half featured the spider's signature colors—"Heavy Body Mars Black" and "Berry Red"—matching the natural hues of real black widows.
Actual spider belly. Image Credit: Nicholas Brandley
The researchers began by observing spider-eating birds. They established seven bird feeders in Durham County, North Carolina, and filled them daily with seeds to attract local birds. On the day of the experiment, they removed the seeds and placed a single fake spider, positioned belly up, at each feeder.
They monitored birds such as Carolina chickadees, northern cardinals, tufted titmice, white-breasted nuthatches, and two woodpecker species as they approached the feeders. The results showed that birds were 2.9 times more likely to attack plain black spiders than the red-marked faux black widows. Smaller birds, in particular, were startled by the red hourglass markings. “The birds would see the red-marked spider model and react with alarm, as if saying, ‘Oh no, get me out of here,’” Brandley explained in the press release.
The birds clearly recognized the spiders’ markings and understood their significance.
Next, the team analyzed the light wavelengths emitted by the markings of two black widow species. Since bird, human, and insect eyes detect different wavelengths, this affects how each perceives color. They discovered that the red markings on black widows are only half as visible to insects as they are to birds.
The researchers then questioned whether the viewing angle played a role, as black widows often hang upside down beneath their webs. This posture exposes the red markings to birds flying above while hiding them from insects below.
To investigate, they constructed 20-inch-tall “widow towers” in the lab and introduced two black widow species (L. variolus and L. mactans), allowing them to build their webs. Consistently, L. variolus spiders, which also have red markings on their backs, positioned their webs higher in the towers compared to the other species. This behavior suggests that L. variolus spiders were elevating their bright markings further from the sight of insects, making them less visible.
