Spiders use a type of aerial dispersal called “ballooning” to move from one location to another. In order to balloon, a spider releases a silk dragline from its spinnerets and when the movement of air relative to the dragline generates enough force, the spider takes flight. We have developed and implemented a model for spider ballooning to identify the crucial physical phenomena driving this unique mode of dispersal. Mathematically, the model is described as a fully coupled fluid–structure interaction problem of a flexible dragline moving through a viscous, incompressible fluid. The immersed boundary method has been used to solve this complex multi-scale problem. Specifically, we used an adaptive and distributed-memory parallel implementation of immersed boundary method (IBAMR). Based on the nondimensional numbers characterizing the surrounding flow, we represent the spider as a point mass attached to a massless, flexible dragline. In this paper, we explored three critical stages for ballooning, takeoff, flight, and settling in two dimensions. To explore flight and settling, we numerically simulate the spider in free fall in a quiescent flow. To model takeoff, we initially tether the spider-dragline system and then release it in two types of flows. Based on our simulations, we can conclude that the dynamics of ballooning is significantly influenced by the spider mass and the length of the dragline. Dragline properties such as the bending modulus also play important roles. While the spider-dragline is in flight, the instability of the atmosphere allows the spider to remain airborne for long periods of time. In other words, large dispersal distances are possible with appropriate wind conditions.