The ballooning of spiders can be explained by the electrostatic interaction between spider silk, atmosphere and the earth. Spiders lack the ability to fly but still they move in the air by discharging silk and moving easily using it. Air drag also plays an important role in the movement of spiders but ballooning effect cannot be just explained in terms of air drag.
The earth is negatively charged and thus any ground based object will have this negative charge. Spider silk is negatively charged. Thus there will be an electrostatic repulsion between any ground based object and the spider silk. Similarly the atmosphere is positively charged which means there will be an attraction between the spider silk and atmosphere.
