Fear the Parasitic Wasp: Spider Zombies Caught in Web of Deceit

When a parasitic wasp skewers an orb spider and glues an egg to its back, she sets off a chain of events that soon alters the behavior and destiny of the spider. A new study from the host-parasite pair’s Japanese homeland shows that, some time after the egg hatches, the spider abruptly abandons its former lifestyle and follows a precisely choreographed sequence of actions that modify its normal web-building activities to produce the best possible home for a developing wasp.1

Zombie Web Design

Transformed by the ichneumonid wasp Reclinervellus nielseni’s sting into an obedient zombie, the orb-weaving spider Cyclosa argenteoalba does more than nourish the wasp’s larva with its own inward parts. The zombie spider serves its new master by modifying its web design to make a stronger-than-normal web devoted to the protection of the wasp’s pupal cocoon. No longer concerned with catching prey for itself, the spider reworks its web to build a hammock of extra-strong non-sticky silks that will ultimately cradle the cocoon.

Kobe University’s Keizo Takasuka and colleagues, who published their work in The Journal of Experimental Biology, painstakingly searched for spiders already parasitized by the wasp and then observed how the spiders’ behavior was affected. They also collected and observed the behavior of normal spiders.

This modified web design is actually an enhanced version of the resting web the orb spider normally builds to protect itself when molting. A spider sheds its exoskeleton in order to grow and is helpless during this time. A normal spider molts nestled in its resting web for just two days, but to accommodate the 10-day period wasps require to pupate in their cocoons, the parasitized spider builds an unusually durable web. It spends 10 hours repeating certain web-building steps over and over, reinforcing the web with additional threads until it produces a web of large-diameter silks with increased tensile strength. It leaves out the sticky stuff. Once its construction operation is complete, the zombie spider sits in the center of the web until the larva consumes the rest of its body fluids and kills it. Then the larva morphs into a pupa and emerges 10 days later as a mature wasp.2

This is a completed cocoon web, a modification of the orb spider’s normal resting web used for molting. Constructed at the behest of its parasitic wasp master, the web built by the “zombie spider” is exceptionally durable, contains no sticky prey-catching fibers, and is decorated with ultraviolet-reflecting silks to deter destructive collisions with birds. Image courtesy of Keizo Takasuka.

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Having completed construction of a cocoon web, this orb spider is killed by the wasp larva that has grown strong on its body fluids. The larva will now morph into a pupa sheltered for 10 days in the unusually durable web the spider has built for it. Image courtesy of Keizo Takasuka.

Shining in the Light

The zombie spider decorates this specialized resting web with ultraviolet-reflecting silks. These deter web-destroying collisions with birds. Scientists used to think that the ultraviolet-reflecting silks in spider webs attracted prey, but their routine inclusion in resting webs of molting spiders and the webs of nocturnal spiders suggests otherwise. The fact that these particular zombie spiders, following their detailed and very pragmatic altered programming, include UV-reflecting décor in their cocoon webs while leaving out sticky fibers altogether is consistent with this view. So is the fact that the prey-capture regions of the normal orb webs studied by this Japanese team were unadorned with UV-reflecting fibers.3

It appears the UV-reflecting webs are God’s design to protect spider webs from being destroyed by bird collisions. Studies have shown the UV-reflecting silks really do deter bird collisions. At least one company is now manufacturing glass incorporating a web of UV-reflecting strips to prevent birds from crashing into windows. This example of biomimicry—technology based on designs found in nature—now protects birds soaring around the observation tower on the Holy Island of Lindesfarne, a center for Celtic Christianity off the coast of England dating back to the 6th century.4

Ultraviolet-reflecting strips incorporated into the glass windows at Lindesfarne’s lookout tower do not impede the view but are readily visible to birds. This design is an example of biomimicry, a manufacture based on the fact that spider’s incorporate UV-reflecting silk into their webs. Image credit Arnold Glass, reproduced from BBC News.

Biomimicry

UV-reflecting silk is just one of many biomimetic applications the study of spiders has provided. For instance, spiders produce several different kinds of silk. A gene that produces a protein in the dragline silk of one species of orb spider has been used to produce transgenic goats that produce recoverable silk in their milk, a protein that can be used to produce fibers stronger than steel for use in artificial joints, bulletproof vests, and parachutes. Biomimetic breakthroughs in technology are imitations of God’s designs. Zombie-creating parasites like this wasp and its parasitized partner can reveal much about the common designs created by God and how even their variations and derangement can work together to perpetuate species in this sin-cursed world.

World Gone Wrong

The fallen world we live in since man sinned supplies an endless variety of examples illustrating what can go wrong. Or, from the point of view of parasitic wasps fulfilling their instinct to multiply using the best available resources, what can go right! How do such parasitic relationships develop?

Parasites survive at the expense of their victims, ordinarily sparing the life of the victim until it is no longer needed. Parasites that manipulate host behavior do so in a way to enhance their own growth or dispersion. Ichneumonid wasps ensure their larvae will be fed by recruiting insects or spiders to donate their bodily fluids to nourish wasp larvae. And the Reclinervellus wasp is not the only ichneumonid that reproduces by providing its larvae with living meals while also manipulating the spider’s web-building behavior to provide each pupa a haven. A Costa Rican wasp, for instance, Hymenoepimecis argyraphaga, follows a similar strategy utilizing the orb-weaving spider Plesiometa argyra.

In fact it was to the Ichneumonidae family of wasps that Charles Darwin referred when he wrote to botanist Asa Gray, questioning how a good God could create such a cruel system. Darwin wrote, “There seems to me too much misery in the world. I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars.”5

God created a perfectly good world (Genesis 1:31) and presented it to man (Genesis 1:26–28). Darwin failed to recognize that God’s good world went wrong because of man’s sinful rebellion. The New Testament reinforces this Old Testament truth, Romans 8:19–23 confirming that that the whole of creation groans in slavery to corruption in the wake of man’s sin. (Read more about this in “The Fall and the Problem of Millions of Years of Natural Evil.”) The death and suffering that afflict not only people but also animals are consequences of human rebellion against God.

Cruelty and the Curse

Darwin complained that he could not envision the cruelty of nature as part of a good God’s design, yet in order for the living things in this sin-cursed world to endure for the past 6,000 years, variations and even derangements of God’s designs have allowed life to go on. Many organisms have adapted by developing defense and attack structures. (Read more about these in “How Did Defense/Attack Structures Come About?” and entomologist Dr. Gordon Wilson’s article on “Divinely Designed Defenses.”) The study of parasites like the ichneumonid wasps will help answer Darwin’s concern by helping us understand what good purposes these organisms were designed to serve in the pre-Fall world as well as the changes that led to the development of parasitic lifestyles after the Fall. Be sure to read more about this in Dr. Matthew Ingle’s article “Parasitology and Creation.”

Spiders today are carnivores, most paralyzing prey caught in their webs and enzymatically digesting and consuming them. (It is curious that most news articles about these zombie spiders paint a horrific image of the spiders’ fate but fail to mention the daily dietary practices of spiders, which are certainly no kinder.) Carnivory and parasitism are both consequences of sin’s curse. We know from God’s Word (Genesis 1:29–30) that animals did not originally eat other animals.

So what did spiders eat? We cannot be dogmatic about the behavior of pre-Fall animals 6,000 years removed from our ability to observe them, but we can reasonably speculate that they could have subsisted on pollen grains caught in their webs. This is not idle speculation. While spiders today are not generally herbivorous, a mostly herbivorous spider living on the Bullhorn acacia tree feeds on the tree’s Beltian bodies.6 And a 2013 study found that 25% of the diet of the juvenile orb-weaving spiders analyzed consisted of pollen grains caught in their webs. The pollen grains in the study were large enough to require active digestion by the spiders’ extraoral enzymes and were likely consumed while the spiders were recycling their webs.7 Thus it is no stretch to propose that before the Fall spiders were herbivorous, and spider webs may have originally functioned as pollen catchers.

But what about parasites like the ichneumonid wasps? If God did not originally design these wasps to turn their hosts into zombies, how did they get to be that way? While we cannot go back and observe the process by which an animal, plant, or fungus became a parasite, we can be confident that all the original created kinds of organisms fulfilled helpful, not harmful, roles in the good world God made. Since the Fall, a combination of mutations and other genetic mechanisms, phenotypic plasticity, natural selection, and environmental changes that have altered available resources have produced many harmful varieties of organisms as well as created both symbiotic and parasitic relationships that ultimately ensure the survival of many species that might otherwise become extinct.

And if the incidence of parasitism in this Japanese pair is any indication, the spider population is not exactly being decimated by the predations of parasitic wasps. It took Keizo Takasuka’s team many days to find 23 parasitized spiders among the 1,615 spiders they inspected.8 Similarly, in a study of zombie ants last year, scientists found that a parasitic fungus infected only a small percentage of the carpenter ants in its ecosystem in order to survive. (Read more about it in “Zombie Ants and Genesis.”) Thus in the post-Fall world in which we live, carpenter ant populations survive to decompose dead wood, wasps survive to continue their valuable pollinating activities, and plenty of spiders survive to continue controlling insect populations.

Usurping the Normal, Not Evolving the New

Further research is needed to discover the chemical agent(s) the wasp or its larva uses to induce the spider’s zombification, causing it to repeat various steps in the normal web-building process over and over while eliminating others. However, a spider’s hormones normally trigger the molting process for which the spider builds a resting web. Therefore, Takasuka and colleagues suspect the wasp is injecting a chemical that mimics the hormone that normally directs the spider to molt.

The same is true of a behavior-altering virus that induces zombie-like behavior in gypsy moth caterpillars. It deactivates their molting hormone, prompting infected caterpillars to climb to treetops where they die and rain their viral load over a wide area. (See “Parasites Affect Behavior of Moths.”)

None of these parasitic relationships or zombie-generating species result from molecules-to-man evolution. This parasitic partnership is an example of an extended phenotype—all the effects a wasp’s gene has, including its effects on another organism (the spider). Parasitic wasps are still wasps, just a family of wasps that now depends on a rather elaborate form of carnivory to reproduce. The spider is still a spider, and even its behavior is a modification of an existing one. Indeed, if these wasps are able to supply a biochemical mimic of the spider’s own hormone, as the authors suggest, such a biochemical similarity exists because all creatures share a common Designer. These and other extraordinary variations were designed by our wise God to be somehow manifested after the Fall. Even though these insidious lifecycles highlight the ugliness of death due to sin’s curse, they still allow the created kinds to reproduce in a fallen world.

Learn more about the beneficial pre-Fall roles today’s parasites likely played in the pre-Fall world in “The Genesis of Malaria: The Origin of Mosquitos and Their Protistan Cargo, Plasmodium falciparum,” how parasitology helps us understand the changes in nature after the Fall in “Parasitology and Creation,” and how deadly venom seems to have developed from harmless but essential biochemicals in “Evolution of Snake Venom: A New Use for Old Genes?” and “Mamba Venom Derives from Gene Duplication.” You can find out more about real-life zombies and parasitic host manipulation in “Zombie Ants and Genesis,” “Parasites Affect Behavior of Moths,” “Brain Chemistry in Rats Altered by Parasite,” and “Zombies Existing in Nature.”