31.10.2010., nedjelja
CATCHING PREY
 Poisoners, ambush hunters and cannibals Spiders mostly eat insects and other arthropods, but are known for eating members of their own species as well. Sometimes they even devour small vertebrae. For hunting prey some species use webs, while others ambush prey or actively hunt it. Spiders turn their pray into liquid with the help of digestive juices, which they either inject into the prey or vomit over it, and then they suck the resulting pulp (extraintestinal digestion). Almost all spiders have venoms that they use for dazing or killing prey. Only few of all known spiders are dangerous to humans. Spider venoms can work in different ways: some disintegrate tissue, while others attack the nervous system. Among Central European spiders just few species are able to penetrate human skin with their jawy. Only the yellow sac spider (Cheiracanthium punctorium) also possesses a powerful venom that can cause strong pains, nausea and high temperature. The most dangerous bite for human being can be given by the Brazilian wandering spider Phoneutria nigriventer. The venom oft his aggressive animal is a powerful neurotoxin which can be lethal even to humans. In contrast to that, theroposidae are harmless. Only a small number of species possess venoms that can harm people, and even if bitten by them, healthy people should not expect lethal consequences. However, a bite itself is painful, since the jaws of these animals are pretty big. Traps and sticky webs – tactics of capturing prey Spiders which weave webs have developed two different methods of catching prey. Some of them produce wool for capturing prey, into which the prey entangles (cribellate spiders), while others use sticky threads (ecribellate spiders). Cribellate spiders produce threads for hunting in such a way that they put smooth and thick wool on their silky threads. This is done with the help o fan organ called calamistrum, a kind of comb placed on back legs. On such threads the prey hangs and eventually gets completely entangled into the web. Ecribellate spiders put small sticky drops on their hunting threads so that the prey gets glued into the web. Since the sticky threads get dry after some time, it is necessary to occassionally replace the web. |
