The flower-mimicking crab spider, often called the goldenrod crab spider (Misumena vatia), is a predator known for its camouflage. This spider can change its body color to blend in with the flowers upon which it hunts. This disguise allows it to become nearly invisible to both its prey and its own predators, making it an effective ambush hunter in gardens and meadows.
The Science of Color Change
The color change in a flower crab spider is a physiological process, not an instantaneous one like a chameleon’s. This slow transformation takes several days and is achieved by controlling a liquid yellow pigment within its body. This pigment, a type of ommochrome, can be secreted into the outer cell layer of its exoskeleton to produce a yellow appearance.
To appear white, the spider withdraws this yellow pigment from the surface cells. This reveals a deeper layer of cells filled with guanine crystals, which reflect all wavelengths of light and give the spider a white look. A change from white to yellow can take 10 to 25 days, while reversing from yellow to white is faster, occurring within about six days. The primary trigger for this change is the spider’s visual assessment of its background.
An Ambush Predator’s Technique
This arachnid employs a “sit-and-wait” ambush strategy. Perched motionless on a flower head, it holds its front two pairs of legs open to seize insects that come to feed on nectar or pollen. Its camouflage conceals it from prey like bees, butterflies, and flies, and also helps it avoid detection by predators like birds.
The spider’s coloration can do more than just hide it. Some research suggests its body reflects ultraviolet (UV) light, which is visible to many insects. This UV reflectance can create a contrast with the flower, making the spider an attractive signal to pollinators. In some cases, flowers with a crab spider on them are more alluring to bees than those without.
Habitat and Geographic Range
Flower-mimicking crab spiders are widespread across North America, Europe, and parts of Asia. They thrive in open, sunny environments where flowering plants are abundant, including meadows, prairies, gardens, and agricultural fields. They are seen on a variety of common plants, adapting their body color to suit their chosen perch.
Some of the most common flowers they use as hunting grounds include:
- Goldenrod
- Queen Anne’s lace
- Daisies
- Yarrow
- White clover
Ecological Role and Human Interaction
In its ecosystem, the flower-mimicking crab spider is a predator of pollinating insects. By preying on these visitors, it plays a part in regulating their populations. The spider’s presence can also influence pollen flow and plant reproductive success within its immediate vicinity.
For humans, these spiders pose no significant threat. While they possess venom to subdue their insect prey, it is not medically significant to people. Flower crab spiders are non-aggressive toward humans and will try to escape or hide if disturbed. Bites are rare and would only occur if the spider were pressed against the skin, resulting in minor, localized irritation.