My students ask this question every year! Since this is Chapter 3, it represents an intercalary chapter, which illustrates symbolism on a macro-cosmic scale. The turtle symbolizes two elements: hardships/struggles and life. As the turtle begins its journey, it is obvious that he is determined to "get to the other side." The narrator describes the turtle as having "fierce, humorous eyes . . .star[ing] straight ahead (Stenbeck 20), which is a good description similar to the migrant workers. Throughout the chapter, the reader learns exactly how hard the turtle must fight to reach its destination. It has many obstacles such as the red ant, and especailly, the truck driver who "swerved to hit it" (Steinbeck 22). Therefore, the turtle, like the Joads and society, must work hard and fight to obtain any desired goal. An individual will encounter hardships in life; but if he or she is as determined as the turtle, then the desired goal will be achieved. In additon, the turtle picks up an oat beard that sticks into its shell. Once the turtle crosses the "burning hot" highway and gets itself turned over, the "wild oat head fell out and three of the spearhead seeds stuck in the ground . . . [and the turtle] dragged dirt over the seeds" (Steinbeck 22). At the end of the chapter, the covering of the seed illustrates the beginning of a new life. According to Ralph Waldo Emerson, individuals and nature are all part of the same spirit or "Oversoul." By covering up the seed, the turtle has initiated a new life for the wild oat. This concept is continued throughout the novel with the narrative of the Joads. The reader must pay close attention to Tom, and especially Rose of Sharon. Also, each intercalary foreshadows events for the Joads, too.
Consider the turtle a symbol of the Joads in general and the plight of the worker in particular. The turtle, like the Joads, is trying to make its way through its life, but is very out of place when crawling across the fast-paced highway…just as the modern worker is left behind by industrialization and the changing economy. The turtle/worker is at the mercy of larger forces. Some might show mercy, like the car that swerves to miss it, but some might also be malign, like the owners who abuse their power. The turtle is also heading their way; it moves on like they do. It is smashed by those going by, and turned over, but it turns itself over and heads on, just as the Joads/workers are trying to do.
The turtle can be seen as a metaphor for both the Joads and the migrants in general: the turtle is tough, tenacious, and unstoppable.
Steinbeck writes, "All over the grass at the roadside a land turtle crawled, turning aside for nothing, dragging his high domed shell over the grass." As the turtle tenaciously carries forward with his life, so too do migrants as they protect both their own lives and the lives of their families.
Further, in another section of the inter chapter, it is revealed that the turtle is transporting a seed in his shell. The turtle not only carries life, but also transplants that life to a new place: “The wild oat fell out, and three of its spearheads stuck in the ground”. This situation is analogous to the way the men end up taking their pregnant wives away where they raise new life in new lands.