Hymenoepimecis is a member of the Ichneumon family with remarkable breeding characteristics. It follows the same basic visual makeup of the average Ichneumon with the characteristic veiny wings and ovipositor. The thing that separates this species from all the others in its family is the fine degree to which it controls its host. Here"s the way it goes about reproducing:

  1. The wasp finds a special orb spider, Plesiometa argyra, and stings it. The sting paralyzes the spider just long enough for the wasp to lay its egg inside of it.
  2. The spider wakes up with a headache and some stomach pain, but continues function normally.
  3. Around 7-14 days pass, during which the larva is gestating and developing. The orb spider is still building its web and capturing prey.
  4. During its last day in existence, the spider weaves a completely and totally different nest- a cocoon web for the wasp. A normal orb spider"s web is intricate and beautiful; it has a complex system of supports and a specialized sticky pattern of rings used to trap prey. The web it spins for the wasp, though, is completely different. It has four supports and they come together at a miniscule four-cornered web with a single thick strand dropping down from its center. From that strand, the wasp"s thick oblong woven cocoon hangs.
  5. As soon as the spider finishes weaving the wasp"s creation, the wasp emerges from the spider, eats it alive, and suspends itself from its newly woven cocoon. The cocoon provides two main benefits for the wasp: protection from rain and protection from predators.

According to the biologist who discovered Hymenoepimecis, fast acting chemicals egested by the larva induce these changes in the behavior of the spider. Let me repeat that again for clarity: This small insect can control an arachnid using complex chemicals, and it can do this before birth!

To me, this is simply the most amazing thing about the natural world.

Source: http://www.museums.org.za/bio/spiderweb/manip_wasp.htm