For this animation I used the "Network From Particles"-Template of the Animation-Node-Addon to add splines between clusters of particles
you can download the blend file here
To create networks from particles is very easy using the Animation-Node-Addon. There are already templates that can be used to speed up your modeling.
All the template needs as input is a particle system. In this animation I used a "Boids" sytem on an ico-sphere.
In the lower right part of the node-editor click on the template menue and select the "Network From Particles"-Menu
Then set the network type to "spline"
In the resulting node network select the object and the particle system you want to use as an input in the "Particles from Object"-Node on the left and select the object you want the resulting splines to be added on the right. If you want to create a new object for the splines, like I did in this animation, click on the small plus icon. This creates a new object named "Target".
Finally you can adjust the bevel depth and resolution or add an extrude value if you like. The size and the behaviour of your cluster can be adjusted on the "Find Close Vertices"-Node. Here you can specify the maximum and minimum distance for a connection or how many connection each node may have.
Animation Node experiment - closed curve
Animation Node experiment - script node spiral
Animation Node experiment - particle cluster II
particle density volumetric material