Kind of Predatory Strategy Adopted

The two main strategies a predator can adopt are attack and ambush. The main tools for attack are adequate sensory equipment, efficient coordination between sensory input and targeted movement, means of locomotion of a level comparable at least to that of the prey, and suitable means for keeping control of the latter until it eventually dies. Squids and their relatives (cephalopod mollusks) provide an excellent example of predators with a beautiful set of adaptations for attack. Squids identify their preys at some distance, mainly by using their very efficient eyes, whose complexity and performances are only comparable, in the sea, to those of their main victims, that is fish (which otherwise are also, often, their predators, or competitors for similar prey items). The information provided by the eyes is rapidly processed in the squid's big brain and the nervous impulse releasing the quick attack to the prey is conveyed by an unusually big nerve fiber (the squid's 'giant axon') along which electrical impulses travel at a very high speed. The next step, that is, the actual attack to the prey, is accomplished by jet propulsion, a kind of locomotion peculiar to cephalopods and immensely more efficient than any other alternatives available to mollusks, which do not possess the articulated appendages typical for most vertebrates and arthropods. Finally, the prey is seized by means of the tentacles, which are provided with series of suckers (sometimes with horny hooks too), and immediately poisoned by a bite that will leave it motionless very soon. Use of neurotoxic venoms that quickly annihilate the reactions of the prey, and eventually speed up killing it, is shared by a variety of predators, from medusas to spiders, from octopuses to vipers. Venoms may enable predators with a fragile body such as medusas to keep effective control of preys, for example, fish, which are quite more robust and mobile than their predators.

Quite different from that of the actively attacking predators is the equipment of the predators capturing their prey at ambush. In this case, interactions between predator and prey will generally begin at a very close distance; thus, the predator's sensory organs are often less developed than in the case of the attack strategy.

On the other hand, many predators are able to mold their immediate environment in order to increase the chance of getting a prey approaching them. For example, the larvae of tiger beetles live in narrow burrows in the soil, with their strongly modified head closing the entrance to it, ready to use the long mandibles to grasp the unwary prey. The larvae of many ant-lion species build small heaps of sand in the shape of a little volcano, then immerge themselves into the crater, from which only their tiny eyes and their sickle-shaped jaws emerge. When biting a prey, they inject into it hydrolytic enzymes that will reduce the soft parts of the victim to a thick juice that the ant-lion larva will eventually suck up.

Spiders are pretty unique among terrestrial predators in their use of costly proteins in the form of silk by which many (but by no means all) of them produce nets or tubes for trapping prey, or at least threads whose vibrations inform the eight-legged hunter that an insect is walking nearby. Besides the nets used by humans for fishing or hunting, the only device comparable to a spider's net are the filter nets produced by some aquatic animals like the marine chaetopterid polychaetes (annelids) or the freshwater larvae of the hydropsychid caddis flies

(insects), which are however better classified with micro-phages rather than with predators, as their trapping devices collect, in addition to tiny prey, a diversity of food items such as algae and organic detritus.

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