Up, Up and Away
Imagine you are a minuscule, new-born spiderling. Early one morning, you and hundreds of your siblings-stirred by the warm spring sunshine and an irrepressible need to enter the world-crawl from a tightly spun egg sac. You nibble at the leftover sac. Competition is fearsome, and a brother spiderling tries to eat you.By the next day, the shrub on which your egg sac was firmly anchored has become a spiderling's Grand Central Station. Little spiderlings are bustling all over the leaves and limbs, criss-crossing their draglines as they climb. Some are traveling the ground, some have gone in circles, still others hang motionless from a selected perch. Tangles of silk drape from every available support.
The dispersal continues, and spiderlings go this way and that. You and many others have an urge to keep climbing higher. Finally, in full, late afternoon sunshine, you have reached the highest bud on your shrub. It already has been an eventful day in your short life, but you turn headlong into the breeze and prepare for the real adventure.
Facing the wind, you stand tiptoe, stretch your eight legs to their fullest and tilt your abdomen upward. Anchored to the limb by a dragline, other threads emerge from the spinnerets attached to your abdomen, and you wait for them to be drawn out by air currents. Soon, several threads from your flexible spinnerets are streaming out in long, wavy filaments behind you. As the threads are seized by the wind, tension on the dragline grows. You can barely hang on. But then something intuitively tells you when the pull on the threads is strong enough to carry you aloft, and you let go. Up and away you soar-a spiderling aeronaut.
Up in the sky, ballooning technique varies. Some air-borne spiderlings climb on their threads like high-wire circus walkers, winding in or streaming out more filaments as need be. In this way, some researchers say, spiders have at least a bit of influence over how high they travel and where they may land. Most just hang on for dear life.
A few species balloon only after reaching adulthood. Some are involuntary conscripts, ballooning because they were simply carried off by a strong and unexpected breeze. Many species don't balloon at all. In Missouri, people tend to notice ballooning spiders most in the spring and fall, though ballooning may take place any time of the year for some species.
How far can spiders expect to travel on their gossamer aircraft? Because spiderlings are so small and difficult to see against a background of white sky, it is impossible to come up with species-by-species accounts and averages. One spiderling may land just a few yards from its take-off point, while its sibling may travel 100 yards. Still other species may go for miles and perish in a lake, or wrap themselves around the neck of an unsuspecting angler.
Charles Darwin observed the arrival of ballooning spiders on board a ship 60 miles from the coast of South America. Arachnologists-people who study spiders-have concluded that most ballooning spiders reach heights of 200 feet or less, though people have seen spiders at 5,000 feet and a few at 10,000.
If you really were a spiderling endowed with intellect and the ability to explain yourself, scientists around the globe would flock to your webside to find out why you balloon. As it is, there are many possible explanations. Most of them include the words "dispersion" and "survival." Perhaps spiders thin themselves out by ballooning in order to minimize fratricide and competition for food.
Some scientists focus on how great numbers of ballooning spiders surely die and, therefore, ballooning can be viewed as a mechanism for population control. Early theories contended that ballooning species possessed an internal drive to colonize new territories.
This has been discounted, however, because researchers have determined that spiders almost always balloon within their circumscribed ranges and don't survive if they drop into inhospitable regions. They're able to adapt somewhat when they drop out of the sky, but not to dramatically different environments.
This fall or next spring, when you're out hiking, fishing on a lake or simply peering across your lawn, watch for ballooning spiders. When you go to brush them out of your face, or pluck one from a companion's shoulder, think for a minute about the tremendous flight it just made. Ounce for ounce, chances are that tiny spider may have just experienced a greater and wilder journey than any human could ever hope for.