Flower crab spider
| Flower crab spider, Thomisidae, Thomisus onustus, Xysticus, Arachnid|
Misumena vatia is a species of crab spider with holarctic distribution. In North America, where it is the largest and best-known flower spider, it is called the goldenrod crab spider or flower (crab) spider, because it is commonly found hunting in goldenrod sprays in the autumn. Young males in the early summer may be quite small and easily overlooked, but females can grow up to 10 mm (excluding legs); males reach 5 mm at most.
Misumena vatia Wikipedia
These spiders may be yellow or white, depending on the flower in which they are hunting. Especially younger females, which may hunt on a variety of flowers such as daisies and sunflowers, may change color "at will". Older females require large amounts of relatively large prey to produce the best possible clutch of eggs. They are therefore, in North America, most commonly found in goldenrod (Solidago sp.), a bright yellow flower which attracts large numbers of insects, especially in autumn. It is often very hard even for a searching human to recognize one of these spiders on a yellow flower. These spiders are sometimes called banana spiders because of their striking yellow color.
The much smaller males scamper from flower to flower in search of females and are often seen missing one or more of their legs. This may be due either to near misses by predators such as birds or to fighting with other males.
When a male finds a female, he climbs over her head over her opisthosoma onto her underside, where he inserts his pedipalps to inseminate her.
The young reach a size of about 5 mm by autumn and spend the winter on the ground. They molt for the last time in May of the next year.
Because Misumena vatia employs camouflaging, it is able to focus more energy on growth and reproduction rather than finding food and escaping from predators. As in many Thomisidae species, there is a positive correlation between female weight and egg clutch size, or fecundity. Selection for larger female body size thus increases reproductive success.
These spiders change color by secreting a liquid yellow pigment into the outer cell layer of the body. On a white base, this pigment is transported into lower layers, so that inner glands, filled with white guanine, become visible. The color similarity between the spider and the flower is well matched with a white flower, in particular the Chaerophyllum temulum, compared to a yellow flower based on the spectral reflectance functions. If the spider dwells longer on a white plant, the yellow pigment is often excreted. It will then take the spider much longer to change to yellow, because it will have to produce the yellow pigment first. The color change is induced by visual feedback; spiders with painted eyes were found to have lost this ability.
The color change from white to yellow takes between 10 and 25 days, the reverse about six days. The yellow pigments have been identified as kynurenine and 3-hydroxykynurenine