Mind-Controlled Spiders and Zombie Ants: Proof That Nature is Horrifying

The loss of free will happens so gradually that the victim does not even realize it is happening. As the invader grows, it assumes more and more control until its host becomes little more than a biological puppet—alive, mobile, and obedient to commands it cannot understand or resist.

This sounds like the premise of a science-fiction movie in which humanity is conquered by alien parasites, preferably just after someone in a laboratory says, “I’m sure the containment system is perfectly secure.” Unfortunately, no alien invasion is required. Nature has already perfected the technique, and it has been using it for a very long time.

One of its more unsettling demonstrations involves an orb-weaving spider and a parasitic wasp. The wasp does not merely kill the spider or eat it. That would be unpleasant but refreshingly straightforward. Instead, it takes control of the spider’s behavior, forces it to construct a protective nursery for its executioner, and then disposes of the unfortunate architect once the work is complete.

In other words, somewhere in the natural world, a spider is being compelled to build its own murder room. Sleep well.

The Wasp That Turns a Spider Into a Puppet

The relationship between the orb-weaving spider (Cyclosa argenteoalba) and the parasitic wasp (Reclinervellus nielseni) is unusual, to say the least. To say the most, it is the stuff of nightmares. The wasp can manipulate the spider’s behavior with a level of precision worthy of the most disturbing science-fiction horror movie imaginable.

The process begins when a female wasp attacks an orb-weaving spider in its web. The attack does not kill the spider. Instead, the wasp temporarily incapacitates it and deposits an egg on the spider’s abdomen. Once the egg hatches, the young larva attaches itself to the spider and begins feeding on its bodily fluids.

For several days, the spider continues going about its business with the larva riding on its back like the world’s least welcome backpack. As the parasite grows, however, the spider’s behavior changes dramatically. It abandons its normal geometric web design and begins constructing a structure suited not for catching prey, but for protecting the wasp larva during the next stage of its development.

The Spider Builds a Nursery for Its Own Killer

The parasite-ridden spider first dismantles much of its existing web. It then begins building a modified version of the structure it would normally create before molting.

This type of web, sometimes called a resting web, lacks the familiar capture areas used to trap insects. Instead, it is constructed with prominent supporting threads designed to provide stability and protection while the spider is temporarily vulnerable.

The altered web also contains conspicuous bands of silk that reflect ultraviolet light. These decorations may help larger animals see and avoid the web rather than accidentally crashing through it. Under ordinary circumstances, this would be useful for protecting a molting spider. Under the present circumstances, the spider is unknowingly installing warning signs around the future home of the creature preparing to kill it.

A normal resting web needs to protect a molting spider for only a couple of days. The wasp larva, however, requires considerably more time. The manipulated spider therefore reinforces the structure far beyond its usual specifications.

Researchers found that the web produced under the parasite’s influence could withstand substantially greater force than an ordinary resting web. Some of its supporting threads were at least 2.7 times as strong as those in a typical structure. The spider has essentially been compelled to upgrade the building from a temporary shelter to a storm-resistant wasp nursery.

One Final Assignment

Once the spider has finished doing its master’s bidding, only one task remains.

The spider moves to the center of the reinforced web. There, the larva kills its host and consumes the spider’s internal tissues for nourishment. When it is finished, it discards the empty remains.

The now-engorged larva then spins a cocoon suspended from the web the spider was forced to build. Protected from predators, wind, rain, and falling debris, it completes its metamorphosis into an adult wasp.

The new wasp eventually emerges, ready to find another spider and begin the process again. It is an exceptionally efficient life cycle, provided one is not emotionally invested in the spider.

Zombie Ants Join the Party

Behavioral manipulation by parasites is not limited to the wasp-and-spider arrangement. Certain fungi can infect ants and alter their behavior so dramatically that the unfortunate insects are commonly described as “zombie ants.”

After becoming infected, an ant leaves the colony and climbs vegetation to a location with conditions favorable to the fungus. At the appointed place, the ant clamps its jaws onto a leaf, twig, or other surface in what researchers call a “death grip.” The ant then dies, securely fastened in position.

The fungus continues growing inside the corpse and eventually produces a stalk-like structure that releases spores onto the forest floor below. Those spores can infect other ants, allowing the cycle to continue. The ant colony, understandably taking a dim view of members wandering home with mind-controlling fungi, may remove infected individuals before they can spread the parasite.

Scientists continue to study how parasites accomplish these remarkable behavioral changes. Chemical signals almost certainly play an important role, although the precise mechanisms vary among species and are still being investigated. In the case of the parasitic wasp, the larva appears to induce the spider to repeat and exaggerate elements of its normal web-building behavior, turning an existing biological routine into something useful for the parasite.

That may be the most unsettling part of the story. The parasite does not need to teach the spider an entirely new behavior. It merely reaches into the spider’s existing programming, selects the appropriate instructions, and adjusts the settings.

Nature, as usual, has taken something horrifying and made it efficient.

Read about more examples of nature being horrifying in this article.

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