A Bug's Life is a platform game in which the player controls Flik throughout settings and a storyline based on the namesake film. The game is divided into five distinct "lands" consisting of three levels each. To complete a level, the player must either find an exit, complete a goal or defeat a boss character. Flik's primary form of offense against enemy characters is throwing berries. By default, Flik throws red-colored berries, which are the weakest form of berry and cannot harm certain enemies. Stronger berries can either be found within a level or received from planting purple-colored seeds. Collecting purple seed tokens increases the range of berries a seed can produce. Aside from increased power, some berries travel faster and can home in on enemies. The strongest form of berry is gold-colored and is capable of permanently eliminating enemies and preventing them from respawning.
Several seeds are scattered throughout the levels. Flik can hoist most seeds over his head and carry them to other areas, although some seeds are embedded into the ground and cannot be moved. Jumping on top of a seed creates a plant that aids Flik in some fashion. By default, all seeds are colored brown and bear plants that help Flik traverse high terrain. The color of the seeds and the type of plant they bear can be changed if Flik collects differently-colored seed tokens within a level. Some plants can restore Flik's health, provide a shield from enemy attacks, propel him through the air, or damage enemies by firing berries. Plants can be uprooted and discarded, which results in a fresh seed appearing in its place.
Flik's health is displayed as a leaf on the top-right corner of the screen, and the player is given six lives at the beginning of the game. When Flik's health is full, the leaf appears whole, but if he is harmed by an enemy or hazard, a bite is taken out of the leaf. Health can be restored by collecting leaves marked with a red cross, which are released from defeated enemies and blue seed plants. Collecting 50 pieces of grain within a level will restore Flik's health completely. If the leaf is completely eaten away, a life is lost. An extra life can be received if the letters F, L, I and K are collected within a level. If all of Flik's lives are lost, it is game over.
Floating telescopes grant a rotating view of either hidden items in a level or the level's exit and the surrounding details. Flik's grain harvester is present in certain levels, and can be used to attract distant grain and permanently kill most enemies while it is worn