Reference: Rodríguez-Gironés, M. A. & Maldonado, M. (2020). Detectable but unseen: Imperfect crypsis protects crab spiders from predators. Animal Behaviour, 164, 83-90. https://doi.org/10.1016/j.anbehav.2020.04.004
Featured Image Caption: Crab spiders can change colors from white to yellow to match the flower they occupy. Although scientists have figured out how they can change colors, it is still unknown why (Source: Lucarelli via Wikimedia Commons).
Dress for Success
We often choose our clothing based on what we plan to do on a particular day. For example, if we are outside on a really hot day, we may choose lighter-colored clothing to stay cooler. If there is someone we are trying to impress, we often get dressed up. When going for a jog, bright, reflective colors make us more visible to reduce the risk of injury. Lastly, if we want to observe some wildlife, we can wear camouflage to blend in. We can easily change our clothes based on our goals for the day.
Some animals can change colors for several of the same reasons that we change our clothes. They may want to stay cool, attract a mate, stand out to inform predators of their foul taste, or blend in to hide from predators and sneak up on prey. You might have heard of chameleons, tree frogs, or octopuses having the ability to change colors. Crab spiders – so-called because they look like crabs when they walk – can change colors too!
Some crab spider species, like Thomisus onustus, wait on top of flowers to capture and eat visitors that approach the flower. These fascinating spiders are easy to identify because their first two pairs of legs are longer than their other two pairs. The longer legs extend and grab unsuspecting insects that land on the flower. Crab spiders consume both unwanted pests and essential pollinators, making them an important member of the food chain.
Crab spiders can change colors from white to yellow by controlling the production of certain pigments. This process, however, takes time (2 to 21 days) so they typically stick to one flower. It is well known how crab spiders can change colors, but it remains unclear why. Some hypotheses follow from the ones mentioned above: crab spiders may change colors to adapt to changing temperatures, increase hunting success, or decrease the risk of being eaten. Researchers Miguel Rodríguez-Gironés and Michelle Maldonado wanted to see if crab spiders are better able to hide from predators (specifically birds) or catch more prey, by matching the color of the flower.
In one experiment, the researchers tied yellow crab spiders to artificial white or yellow flowers and recorded which spiders the birds ate. In another experiment, they released crab spiders on live corn daisy (yellow) or mallow (purple) flowers and observed their interactions with visiting insects. Birds ate double the yellow spiders that were on the artificial white flowers than the artificial yellow flowers. Additionally, yellow crab spiders released on the purple mallow flower were three times more likely to catch insects than spiders on the yellow corn daisy.
Can you Spot the Spider?
On live plants, blending in with the flower was unnecessary for yellow crab spiders to successfully capture the insects. In fact, the yellow spiders were most successful on the purple mallow flowers, where they were more conspicuous. Although visible on white or yellow, the yellow spiders were eaten by birds more frequently on artificial white flowers where they stood out the most. Therefore, color matching may not be important for capturing insects, but it is important for hiding from hungry birds. Just like we use camouflage to remain undetected by wildlife, crab spiders use camouflage to hide from predators.
By reducing the risk of being eaten by birds, crab spiders can continue to reduce pest populations for farmers, gardeners, and wild-growing plants. Studies like these are also important for understanding relationships between predators, like the crab spider, and pollinators that help plants reproduce. If you think crab spiders and their color-changing abilities are cool, you can go outside and find them yourself. Just look at a flower, especially yellow, white, or purple ones, and you might find a crab spider waiting for its next meal. Visit this site to see what crab spider species are in your area!