What is the theme in Prey by Michael Crichton?

The desire to succeed is an important theme. It's Julia's desire to succeed that drives her to take actions and risks that she would likely have avoided under normal circumstances. Though Julia is infected with a swarm when she offers the explanation of wanting to succeed to explain her behavior to Jack, it seems likely that it is the truth. Jack seems to believe that it's true, especially based on the emails he recovered from Julia's computer. Julia says that funding for their project was going to be taken away in a short period of time. While she's busy trying to get funding for a commercial aspect - the medical technology program - she's only seeking to gain some financial input to save the company. She seems still to be intent on the need to successfully complete the project. This driving need is also at the heart of the reason the swarm is free.