In the depths of the tropical rainforests of Xishuangbanna, China, a unique natural phenomenon awaits the observer’s discovery. Look closely at the picture below, you will find two exquisitely hidden spiders. At first glance, one might only notice a male spider, but in fact, beneath it lurks a much larger female spider. Scientists from Yunnan University studying this phenomenon have proposed a hypothesis: The male and female pair of crab spiders may be engaged in a kind of cooperative mimicry. The male appears brown, similar to a flower’s stamen, while the larger female spider, with a pale amber color, seems like flower petals.
Crab spiders differ from other spiders in that they generally do not spin webs but rather adopt an ambush approach, quietly lying in wait on flowers for small arthropods, such as bees and flies, to approach before quickly capturing their prey. This cooperative mimicry behavior of such spiders may be to enhance their survivability and hunting efficiency in the wild, especially during the several days of mating.
As for the explanation of this cooperative mimicry, there are different views. For example, Gabriele Greco, who is highly interested in the biomechanics of spiders, thinks that the male spider standing on the back of the female might simply be a common behavior during the mating process.
The mimicking and camouflage ability of crab spiders is well-recognized. For example, female crab spiders (Thomisus spp) of the Xishuangbanna region can integrate themselves with the surrounding environment, such as with Gloxinia plants, to both avoid predators and better catch prey. Usually, females wait quietly and capture the incoming prey, while the smaller males are often on the move in search of mates.
The ability to change color is a sophisticated chapter in the art of crab spider camouflage. Especially the goldenrod crab spider (Misumena vatia), which can switch between yellow and white to adapt to the flowers they inhabit. When in a yellow environment, they can secrete yellow pigments to gradually turn yellow; conversely, in a white environment, they expel the yellow pigment from their bodies.
However, the color-changing process requires time. Turning white may only take a few days, but returning to yellow can take up to 25 days because they need to re-synthesize enough yellow pigment. Notably, the color-changing ability of crab spiders is visually triggered—once the vision of the spiders is obstructed, they are no longer able to adjust their body color according to environmental changes.
Interestingly, crab spiders occasionally choose to camouflage with flowers that significantly mismatch the color of their bodies. Some female crab spiders also have red stripes or spots, which are quite conspicuous from a human perspective, but since other arthropods generally cannot distinguish red, the camouflage of the spiders remains very effective.
Crab spiders’ front two legs are not only longer and stronger than their hind legs, but their swift movements and potent venom allow them to capture insects much larger than themselves, such as bumblebees and butterflies. Once these unfortunate prey are caught by the powerful long legs of the crab spiders, the possibility of escape becomes very slim, followed by a fatal bite and injection of venom by the crab spiders.
Unlike some spider species, crab spiders do not capture their prey by biting with their fangs. They use their chelicerae to puncture their prey and then suck out the bodily fluids through the wound. Eventually, the prey’s body remains almost intact, making it seem as though they are still alive.
In this predatory behavior, female crab spiders may regard the male as food after mating. Older male crab spiders, generally much smaller in size compared to females and further disadvantaged by reduced speed and agility, are more likely to be preyed upon.
Some crab spiders adopt impressive camouflage tactics to obtain food. For instance, ant-mimicking crab spiders (Amyciaea lineatipes) hunt by imitating the appearance and behavior of ants. They lift their front legs as if waving ant antennae and use silk threads to ambush passing ants.
Then there are species like the bird-dropping crab spider (Phrynarachne), whose camouflage is so convincing that they not only resemble bird droppings in appearance but are even said to emit a similar odor. Research indicates that this disguise not only prevents predation but also attracts prey. For certain insects, bird droppings are a source of nutrition and an oviposition site, so flies may be lured by such “fresh” prey.
The unique predatory and camouflage strategies of crab spiders demonstrate that whether imitating flowers or bird droppings, they always find ways to ensure their survival and reproduction.