They change colour to
merge with flowers
LIVING among flowers, the crab spider is expert mimic. It adorns its body with such colours and patterns that they match completely with its surroundings. The result is it merges so well with the flowers that it is almost impossible for the casual observer to spot it. Wearing this cloak of anonymity, the arachnid is able to ambush its prey without much difficulty. Instead of spinning a web or chasing the prey, as most of its cousins do, crab spiders sit motionless amongst the petals and anthers of insect-pollinated flowers and wait for insects, such as butterflies and hoverflies to alight.
When any pollinator touches down upon the flower, the camouflaged predator pounces upon the unsuspecting visitor and grabs its head and bites into its mouth parts, reversing the normal flow of nutrients, and sucks out the body fluids. Desiccated butterflies are often left resting on the flower.
The cryptic coloring
is important. In an experiment with dandelion flowers, a scientist
once placed yellow pebbles on half the flowers and black pebbles on
the rest. Insects were very reluctant to visit the flowers with the
conspicuous black pebbles, indicating that without the flower-matching
colours a crab spider would have a very lean time indeed.
In the tropics, there are colourful species of praying mantis that mimic the flowers on which they sit. These are the flowers mantids, and although they are much larger than the crab spiders, they are only visible when they move. One of the most beautiful is the so-called devilís flower, an African mantid with red-and-white legs. White orchids in South-East Asia have their own deadly orchid mantis that resemble white petals.
Praying mantids also mimic leaves and sticks, and they get their name from the prayer-like attitude of their first pair of hinged, grasping limbs that can extend forward instantly in one-twentieth of a second to snatch a meal. They have insatiable appetites and are skilled predators. One specimen was seen to snatch and eat 10 cockroaches in a span of only 3 hours. Mantids come in all shapes and sizes, some as large as 6.5 inches long, and catch small frogs and lizards.
Perhaps the most unlikely predators to lie in
wait on a branch are the larval stages of moths. The Hawaiian looper
caterpillar, along with 20 related species, is killer caterpillar. It rests on a
leaf or stem, grasping it with its rear suckers, and extends itself out at an
angle, looking to all the world like a straight, green twig. If however, fly
would come close and touch sensitive hairs on its back, the caterpillar bends
rapidly and seizes the prey in its grasping forelegs. With the victim firmly
caught, it straightens out once more and devours the prize.