system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do flies react faster than us?
gpt
Flies are smaller and simpler.

When you start talking about fractions of a second and automatic nerve reactions you can literally take into account how long it takes for a nerve impulse to get from point A to B.  Because our nerves are longer, it takes more time for us to know the nerve sensed something and more time for our reaction to get where it needs to be.

We're also a much more complicated creature and the way we move on our feet is much more complicated than twitching fly wings.  A move like "jump out of the way" is going to be hundreds or thousands of little movements and coordination over the entire body to move your trunk and limbs into the correct spot, wrap toes, push off, and stay balanced during the whole operation.  A fly just sort of twitches in the opposite direction of a stimulus, or pulls wings and stops moving because gravity will drop them to a safer spot.