The parasitic fly Arachnidomyia lindae.
Read aloud For a Mexican spider, a fly is not always a welcome meal, but sometimes a nightmare: The fly "Arachnidomyia lindae" plunges directly into the center of the spider web and shakes the threads like a trapped insect. But the apparently suicidal action is purely calculated, American biologists have observed. The net is not sticky at this point, and the fly can use the vibrations to lure the spider away from its clutches, reports the journal "Nature" in its online edition. If she succeeds in doing so, she will lend her own offspring to the eggs of "Metepeira incrassata", as George Uetz from the University of Cincinnati and his colleagues have discovered. The fly maggots penetrate into the eggs, then to eat them from the inside in peace? if the spider does not discover it before.

The list does not always work. Some spiders recognize the enemy fly already at the approach to their totals. Shaking it on the net, she is in a dilemma: Protects her offspring or follows her curiosity and looks to see if it is not actually to make loot. "After some pointless reciprocation, the spider separates the connection between her ice pack and the net, " says Uetz. The vibrations can no longer distract you. Once the danger is over, she repairs the damage again.

The spider Metepeira incrassata lives in huge colonies that can cover more than 160, 000 animals.

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