No i dont use any event functions
The spider just check all the spiders in a definded range and get via -vec_to_angle an angle force away of the spider in their way and simply add the forces to a final force if there is more than one spider.
Additionally they are speeding per spider in range a specific amount down so they won't get to the same position.
One other important thing is that the spiders dont check only if there is a spider in range they check too if the spider is walking towards the other spider AND the other spider towards the spider then the angle will be calculated.
If the spider only walks towards the other, but the other doesnt walk towards the spider the speed will be decreased.

(wow, what weird sentences xD )

hmm i dont know if using a quadtree would improve the collision avoinding but i have an idea how i can add some pathfinding to those creatures or a way how they could walk randomly through a maze without running against walls and without tracing i think i will do that today

EDIT: @ Joozey: Okay i will do that xD