Picture this scenario: you are walking through a field populated with flowers of all colors. As you glance to your left, you catch the sight of a bright white spider resting on the petal of a flower, looking at you curiously. Your instinctive drive kicks in and you begin to assess the danger of the situation: Is the spider aggressive? Does its bite hurt? Is it venomous?
Well, worry not, because odds are its just a common goldenrod crab spider (Misumena vatia). These spiders are known for their camouflage abilities and habit of hanging out around flower patches. They are one of the most common species of spider in the northern hemisphere and exist in essentially every country north of the Tropic of Cancer. Females of the species are generally a bright white color and are capable of changing their color to match the flowers that they feed on. Males, on the other hand, are mostly yellow and are noticeably smaller than females. They are also sometimes called flower crab spiders.
Crab spiders are part of the taxonomic grouping Thomisidae, a family of spiders that contains 2,100 species spread across 175 genera. Spiders of the Thomsidae family generally do not build webs to trap prey; they instead actively hunt and will hide and ambush their potential meals. The same is true for goldenrod crab spiders; they are proficient ambush hunters and will lie in wait till the perfect moment, hidden by their camouflage.
Most goldenrod crab spiders come in at a length of about 7 mm for females, and 3 mm for males. Females have been observed to reach sizes up to 10 mm in length, though males rarely exceed 5 mm. Like all spiders, they have two main body segments, the cephalothorax and an abdomen. They have 8 legs splayed out to the side, giving them an appearance and gait similar to that of a crab. In general, the 2 front-most legs are longer than the others. While they do have a chitinous exoskeleton, goldenrod crab spiders tend to be more flexible, on account of their hunting habits.
Aside from their distinctive color, goldenrod crab spiders can be distinguished from other crab spiders by the shape and placement of their eyes. They have 2 rows of eyes, the top row of which is straighter and larger than the bottom row. All the eyes have a unique shape that is wider at the bottom and narrower at the top. Surrounding the body are tiny fine hairs that often pick up the pollen of the flower on which the spider is hiding.
Goldenrod crab spider exhibits an obvious sexual dimorphism. In addition to differing sizes, females tend to start off life as a bright white color, and later learn to adapt and change their color at will to their surroundings. Most females tend to have two lateral stripes that are a reddish pink color. Most males are born a yellowish or white color, and mostly stay that color their whole lives. males also have proportionally longer legs than females. Females also tend to have a rounder, more spherical abdomen and closer together eyes. Up to 85% of an adult female goldenrod crab spider’s weight and body mass is due to the eggs that she carries from birth.
Goldenrod crab spiders are obligate hunters and directly attack their prey. Unlike many spiders that create webs and wait for their unsuspecting food to wander in and become trapped, goldenrod crab spiders will stake out a particular location and lie in wait for their food. Once an unsuspecting victim comes by, the will pounce into action, extending their front legs rapidly to snatch and draw their prey closer. Though small, they are aggressive hunters and can take down prey larger than them. They also have very keen eyesight for their size, a trait shared with other species of hunting spiders.
Goldenrod crab spiders subsist mostly on a diet of other pollinating insects, such as bees, flies, butterflies, and wasps. Their venom is particularly toxic to bees. In many cases, they themselves end up playing the role of pollinators, as pollen gets stuck to their leg hairs and is transferred from flower to flower. Goldenrod crab spiders hang around many different kinds of colored flowers, including daisies, lilies, sunflowers, and (obviously) goldenrod flowers. They can be agriculturally beneficial as they feed on insects that can damage crops, like flies and grasshoppers. They also can actually increase seed production of plants, as they eat insects that can damage plant seeds.
Once they bite, their fangs inject venom into their prey which begins digesting them from the inside out. Even though their venom is powerful enough to kill foes almost three times their size, they are not a danger to humans. Larger female specimens are capable of giving a sharp bite like a bee sting, but their fangs are too small and do not contain enough venom to cause any real harm to humans. At most, they can give a wound about the size of a mosquito bite. Although they do not make webs to capture food, they can still produce silk and will often create strands to anchor themselves to flowers or to wrap themselves in a protective coating.
Mating season for goldenrod crab spiders is a relatively unceremonious affair. At the height of summer, male specimens will jump from flower to flower, looking for a receptive mate. During this time, males often fight amongst each other for female attention, resulting in many male specimens with missing legs. Once finding a mate, they will crawl and hang from the underside of her stomach, where they insert their pedipalps to inseminate the female. The female will then find a cool an dark place to lay her eggs, which she will then guard until they hatch. In some cases, the female will wrap her eggs in a protective cocoon of silk. Goldenrod crabs spiders have been observed to engage in sexual cannibalism, and sometimes an unlucky male may find himself the meal of a larger female after copulation. They typically only resort to eating each other if resources are slim. The probability of males being cannibalized increases with age, most likely because male spiders lose speed and agility with age.
Eggs normally take a few weeks to hatch. The newborn spiders come in at around 5 mm in length and are morphologically similar to adult specimens. They reach full size by mid-winter and go through their last molt into adulthood during May. After that, they leave in search of mating opportunities. Scientists are still not exactly sure of the average lifespan of goldenrod crab spiders but it likely varies depending on sex. Males are estimated to live an average of 12 to 18 months and females up to 2 years, but some females can reportedly live up to 6 years in ideal conditions.
The most striking feature of goldenrod crab spiders is their camouflage abilities, in particular, those of the female. Female goldenrod crab spiders possess the uncanny ability to alter levels of pigment in their skin to match the color of the flowers they frequent. Females start off as white, then will inject a yellowish pigment called kynurinene into their skin cells to match the shade of nearby flowers. If the spider then goes back to white flowers, they will remove the pigment from their cells and excrete it from their bodies. Most of the time, it takes about 25 days for the spider to turn from white to completely yellow, and about 6 days to turn from yellow back to white.
The change in color is regulated by visual feedback. That is, goldenrod crab spiders can look at a flower and regulate the injection of pigment to exactly match the color of that flower. Painting over a spider’s eyes will prevent it from changing color to match the flower. Goldenrod crab spiders are extremely good at matching colors; they can match wavelengths of reflected light with high precision and are difficult to see with the naked eye.
The camouflage ability doubles as both defense and offense. On the one hand, camouflage keeps them hidden from potential predators, like birds, lizards, insects, and other arthropods. Their camouflage also allows them to play effective offense by hiding them from unsuspecting prey who stop by a flower for a quick meal. The camouflage lets them expend energy more efficiently. It takes much less energy to lie in wait for prey to ambush than it does to actively hunt them. This hunting strategy allows the spider to focus more energy on reproduction, particularly females for whom reproduction is an arduous process. Females require a regular source of large prey in order to have the healthiest brood possible.
Males do exhibit some degree of camouflage ability, though not to the degree and precision of females. Males did not evolve to have a need for camouflage, as they do not have an evolutionary need to conserve energy for the rearing of offspring.