It's always worth checking puddles formed after heavy rain. The lighter insects such as Springtails get washed into puddles in significant numbers and because they can stand on the surface, they tend to congregate together in 'rafts' as seen in these images. Other heavier insects such as ants (one seen here) and mites can be seen using these rafts to survive. Eventually, wind blowing across the puddles pushes the rafts to the water's edge and the Springtails disperse.