A wasp descends onto the yellow petals of a black-eyed Susan, unaware that a camouflaged crab spider – once as white as a wedding dress, now the color of a school bus – lies in wait.
Nectar-filled flowers serve as lethal hunting grounds for these arachnids, which have mastered the art of avoiding detection by assuming the color of their backgrounds and ambushing insects unlucky enough to land nearby.
Though researchers began documenting this phenomenon more than a century ago, a new study led by University of Nebraska-Lincoln doctoral student Alissa Anderson has become the first to quantitatively measure the rate of color change in a spider.
Anderson and a colleague regularly took digital photos of the Misumenoides formosipes species of crab spider after placing white specimens on yellow flowers. By using Adobe Photoshop software to quantify the colors captured in each shot, they derived an equation that describes the time it takes M. formosipes to morph into various hues of yellow.
The study reports that white crab spiders begin transforming within a day of settling on a yellow flower, with some specimens needing as few as three days to fully assimilate.
“There have been previous reports for the rate of color change in another species of crab spider, but they were subjective estimations,” Anderson said. “Shifting to a quantitative measurement provides an objective assessment that can serve as a comparative baseline for further empirical studies with this and other species.”
Anderson also sought to test the hypothesis that white-to-yellow transformations take less of a physiological toll – and less time – than opposing yellow-to-white makeovers.
When the authors placed yellow crab spiders on white flowers to assess their transformation rate, however, the arachnids typically chose to depart rather than modify their color. In contrast, white specimens on yellow flowers often remained, morphed and enjoyed greater hunting success as their color began to resemble that of the petals.
“The behavior of yellow females abandoning white flowers suggests that there are greater costs associated with that direction of color change,” Anderson said. “Otherwise, we would have expected the yellow females to stay and simply change their color, as the white females on yellow backgrounds did.”
The authors noted that these findings generally align with those of previous research, which has cited physiological costs as a likely explanation for the rarity of color-changing among predatory animals.
The study appeared in the most recent edition of the journal Ecological Entomology. Anderson co-authored the paper with Gary Dodson, professor of biology at Ball State University.