The transition from treatment to storyboards took on an extra layer of complexity due to the profusion of storylines. Where "Toy Story" focused heavily on Woody and Buzz, with the other toys serving mostly as sidekicks, "A Bug's Life" required in-depth storytelling for several major groups of characters. Character design also presented a new challenge, in that the designers had to make ants appear likable. Although the animators and the art department studied insects more closely, natural realism would give way to the film's larger needs. The team took out mandibles and designed the ants to stand upright, replacing their normal six legs with two arms and two legs. The grasshoppers, in contrast, received a pair of extra appendages to appear less attractive. The story's scale also required software engineers to accommodate new demands. Among these was the need to handle shots with crowds of ants. The film would include more than 400 such shots in the ant colony, some with as many as 800. It was impractical for animators to control them individually, but neither could the ants remain static for even a moment without appearing lifeless, or move identically. Bill Reeves, one of the film's two supervising technical directors, dealt with the quandary by leading the development of software for autonomous ants. The animators would only animate four or five groups of about eight individual "universal ants". Each one of these "universal ants" would later be randomly distributed throughout the digital set. The program also allowed each ant to be automatically modified in subtle ways (e.g. different color of eye or skin, different heights, different weights, etc.). This ensured that no two ants were the same. It was partly based on Reeves's invention of particle systems a decade and a half earlier, which had let animators use masses of self-guided particles to create effects like swirling dust and snow.