On the wonderful origins of the ogre-faced spider
Around 66 million years ago, the world saw more than just dinosaurs. Early primates were beginning to flourish, flowers had finally begun to bloom, and a giant meteor was en route to destroy 65 percent of Earth’s larger terrestrial animals. But it was also a time when a certain class of spiders began to develop some, let’s just say, ogre-esque qualities. These qualities would eventually become what we know today as the ogre-faced spider.
The ogre-faced spider has many idiosyncrasies: It has the eyes and mandibles of an ogre-like creature, it has a style of attack unique to it and its ogre-faced brethren, and it has a ubiquity that suggests an early evolutionary trajectory and strong adaptation to its niche. Amazingly, each of these idiosyncrasies is related to the same suite of evolutionary adaptations. This is the story of how these adaptations combined to bring us one of the most bizarre spider species in existence—in all its grotesque glory.
A Land Before Ogres
While the earliest evidence of spiders dates back to 380 million years ago during a time called the Devonian, the arrival of our ogre-faced friends didn’t occur until a few hundred million years later; they didn’t arrive until the Early Cretaceous, a time when carnivorous dinosaurs began to rule the Earth.
The Early Cretaceous, which lasted from around 146 to 100 million years ago, was a drastically different time period than today. The Earth’s atmosphere was much warmer, yielding the majority of Earth’s crust to be covered in thick, dense forests. But the Earth itself was much different: The continents that stood above water were largely connected as supercontinents. These supercontinents help explain the ubiquity of our ogre-faced friend, along with many other species of spider.
The landmass from which the ogre-faced spider emerged was called Gondwana. This giant supercontinent was composed of what we know today as South America, Africa, Antarctica, and Australia. If we look back to the rock of the Early Cretaceous, we find early iterations of the species on all of these different, now-separated continents.
The study of how species shift and migrate with geologic time is called biogeography. Biogeography is what explains the origin and distribution of the ogre-faced spider and its closely related kin. And now that we’ve described where this spider came from and how it spread across the world, we can describe how it got to be so ogre-y.
When the ogre-faced spider began to diverge in the Early Cretaceous, it developed a suite of traits that, like a few other spiders, would separate it from most of its arachnid brothers and sisters. The most significant of these changes would occur to its visual system.
Most spiders, in case you were unaware, have exceptionally poor vision. Because they have adapted to a life in which their sticky web does most of the work of catching prey for them, they never really had to develop that great of eyes. All they would have to do is cast a net, wait for some poor, unsuspecting insect victim to fly into it, and then use the vibrations of that struggling insect’s body to find and eat the thing. This isn’t the strategy that the ogre-faced spider developed.
Rather than develop a sticky web to ensnare its prey, the ogre-faced spider—along with a few other species like the wolf and jumping spider—developed better vision. This vision helped them to find their prey to hunt it down and eat it. Their webs remained un-sticky and specific to ensconcing their babies in their characteristic silk cocoons.
The importance of vision for the ogre-faced spider is what led to its ogre-y face. Of its eight eyes, two would develop into what are now called its posterior median eyes (named for their anatomical orientation: “posterior” meaning in the back, “median” meaning in the center). Wolf and jumping spiders, as a minor point of contrast, would develop enlarged anterior median eyes, but that is neither here nor there.
The enlarged set of posterior median eyes that the ogre-faced spider developed helped it to identify and capture prey. They have deep cones, which can detect subtle variations in light rays, and a suite of hyper-sensitive photoreceptors which scientists say can detect light in dark conditions up to 2,000 times better than humans. These eyes helped to recognize minute shifts in light in the surrounding environment and use those shifts to direct its attacks. This hunting strategy, as you’ll see, is something to be admired.
When Ogres Attack
According to arachnologists, the ogre-faced spider has an exceptionally strange way in which to capture its prey. First, it will fashion a web and hold it with four of its eight legs. Then, it will dangle under nearby foliage, hanging head-down to disguise itself as a twig. Then, as if the spider felt obligated to make us balk in bewilderment, it “defecates” on the ground beneath it to create a target. Once an unsuspecting insect crawls over this defecation, the ogre-faced spider will lunge forward and trap it.
When Ogres Took to Night
Much of the ogre-faced spider’s hunting happens at night. This is in part why the species has developed such exceptional vision—not only does it have to spot and actively identify its prey, but it has to do so in darkness. The conditions led to one of the most complex simple eye’s (an eye with only a single lens) in the animal kingdom.
The transition of the ogre-faced spider into nighttime terrain made sense: Birds, lizards, and other spider-eating foes make their rounds most often during the day. If you, as a prey animal, can push your habits into the nighttime world where fewer of these animals hunt, you might be better off. And this is what happened to the ogre-faced spider—it grew to inhabit the night.
During the day, the spider again plays into disguise, sleeping in positions that resemble twigs or leaves. Either way, the thing remains hidden and quiet during the daylight hours. Only with night will the ogre-faced spider show its ogre-like face.
The story of the ogre-faced spider is one of evolution, separation, and specialization. While it may have the odd tendency to use defecation to catch its prey, it also has the privilege of having one of the most complicated set of simple eyes around. Let’s just be happy these ogreish spiders aren’t any larger than they are.