Reaction Times and Reflex Action

What is a Reflex Action?

A reflex action is a movement that is performed independently of an organism’s will. In other words, this action is involuntary and nearly instantaneous. Typically, this type of behaviour is exhibited when an organism reacts to a stimulus that can potentially cause harm if it does not react in time. An example of reflex action is observed when we touch something hot and our fingers are instantaneously jolted away from the source. Similarly, animals and even some plants exhibit reflex action which is far superior to that of humans.

How is Reaction different from Reflex Action?

A reaction is usually a voluntary action executed to perform a specific function, such as attacking prey, evading predators, etc. The primary difference between reaction and reflex action is the neurological pathway involved. In a reflex action, electrical signals are sent directly to the spinal cord, without routing through the brain. This is why reflex actions occur significantly faster than reactions.

Reaction Times in Animals

House Flies

Flies are very hard to hit if we try to swat them. This is due to the fact that a fly’s reaction time is 20 milliseconds, which is lightning quick when compared to a human’s reaction time – which scientists have estimated to be at least 100 milliseconds.


Usually, jellyfish have seemingly fragile bodies, making them seem mortally delicate. However, jellyfish are able to hunt prey much larger and robust than themselves by using their secret weapon – nematocysts. These are tiny, hair-like projections that are essentially specialized cells shaped like miniature harpoons. When an animal brushes across these structures, the nematocysts thrust into the animal’s body at speeds of over 700 nanoseconds (0.0007 milliseconds). As a result, it can cause excruciating pain and potentially life-threatening reactions.

Condylostylus (Genus)

Condylostylus are a genus of flies and are thought to have the fastest reflex response in the animal kingdom. Scientists have measured its reflex response time to be less than 5 milliseconds. For comparison, an average human blink is between 100-400 ms long.

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