Why do small organisms make faster movements than big organisms?
It's a general phenomenon that the time scale correlates with the size scale of complex systems. 
Energy consumption is the main concern dealing with the speed for biological organizations.
In the absolute sense, a turtle has a higher speed than a small bug. But based on their sizes, the bug seems much quicker and faster. So we need to normalize the speed with the size scale which we can temporarily call 'fastness". 

Here is the relationship between the fastness and the mass:



Where u is speed of the organism, M is mass, alpha is a constant which we assume that the metabolic energy is related to the body mass of the organism with a power law.

The final equation says that if alpha > 1.67 then the larger would be faster. But our observation tells us that the smaller the faster. Therefore, we know alpha &lt; 1.67. 
In fact Kleiber's law tells us that the alpha is about 0.75. 

You can check some numbers related to some animals here