The fastest terrestrial animal is the cheetah; it is scary fast, to the tune of 70 mph over short distances. From a dead stop, the cheetah can hit 60 miles per hour in just three seconds.

If we look up in the sky, there are some pretty fast animals there too. The peregrine falcon is considered to be the fastest bird, hitting over 220 mph when in its hunting dive.

The difference is that this speed is achieved with the aid of gravity, it is only in diving that they can go this fast. In horizontal flight, the peregrine can manage only a measly 55-60 mph, not quite as good as the cheetah.

If you want top speed in flapping flight from a bird, bet on the white-throated needletail. It used to be considered a member of the swift family (appropriately named), but is now in its own genus. With a tail wind and the proper motivation, these small birds can reach speeds of 100 mph.

If we drop down into the seas, we can look at speed in the fishes. The sailfish is considered to be fastest. It is of course built in a streamlined fashion, meant to build the speed needed to catch the fish and octopuses it eats. It has been clocked at 68 mph, which in my book makes it faster than the cheetah, since it is moving through water, a much more dense medium as compared to air.

So how do bacteria stack up against these speeds? Not too well, despite what we saw in the first video. The fastest bacteria, members of the Vibrio family, move about 200 µm/sec – this is about 0.00045 mph.

Because we are looking at a very small area under the microscope, it appears that the bacteria are covering a good distance. But at 1000x magnification, the least magnification you would need to observe bacteria, the field is usually just 500-800 µm across (0.02-0.03 inches). This makes the bacteria appear to be moving quickly.

Like the fish, bacteria are moving through an aqueous (water) medium, so the density is much greater. But it is even worse for them because of their small size. The effects of density are much larger on small organisms, sort of like us trying to walk through a pool filled with caramel (not a bad idea).

But what if we measured speed in a different manner, say….. bodies lengths per second. Vibrio are approximately 2 µm (0.00008 inches) in length and they move about 200 µm/sec. This is about 100 body lengths per second. Now that seems pretty fast, especially for swimming through something thick.

How does that compare to our other candidates:


So the bacteria are pretty fast, it just depends on how you measure it. But the needletail still holds its own, even though it is only traveling through air. Comparatively, Usain Bolt moves at a top speed of about 6.2 body lengths/sec. Since humans walk upright, we could measure him at body depths/sec, which makes him sound faster, about 30 body depths/sec (assume 15 in body depth). But we don’t all run like Usain Bolt.

In the table above is a couple more examples so that we can find an overall winner. As always, nothing seems to top the insect world, the Australian tiger beetle can move at over 2500 body lengths/sec, while the darner dragonfly shown above is merely the scientifically confirmed fastest flying insect. However, if you want to go with the most recent estimate for the male horsefly (Hybomitra hinei wrighti), we are talking about speeds of 145 kph when he's in pursuit of a female- typical male behavior. That works out to roughly 4000 body lengths/second!

http://biologicalexceptions...ow-fast-is-fast.html

Must be something like measuruing an RC cars scale speed.

I like how we measure ourselves in body depths to make us seem faster. Though with our setup, our stride length is not proportionate to other mammals. this could bring up a great debate on figuring in stride length proportionate to our body length/depth

Funny that they discount gravity, but a tailwind counts.