This is a office gag (I know, I know, I'm a terrible person) I used many years ago but has been reborn with 3D printing. This uses a black plastic 35mm film container, a spring (SP-9705 Handyman spring; 11mm X 54mm X.8mm) and two printed pieces to hold the spring in place and "launch" a few dozen plastic ants and spiders when the film container is popped open. See the video for how to load and use. Perfect for your next picnic or perhaps your neat freak cubical mate. Just leave it loaded and walk away; "they will open it if you make it".
Film containers are still around and/or you can try a camera shop if you can't find one. See video of this in action; https://www.youtube.com/watch?v=KEJnj-6tYa8