There was a throwaway line in one of the Spiderman movies that said that there are spiders out there that react so fast it borders precognition. This is where is “spidy sense” comes from. Is there any truth to this? What is the fastest reaction time any animal has? I mean some animal out there has to hold the record even if we do not know it. I suspect the quickest acting animal to stimuli is probably an insect or some type of spider. Given what we know of nervous systems what is the fastest something could respond to stimuli
Note that the distance that any electrical impulses need to travel (round trip) would be much less for a small creature than for a human; that likely has something to do with it.
Not as likely as you’d think, actually. Since neural signals travel at about 330 ft/s, if reaction-time was purely based on the conduction of said signals, then the reaction-time of a 5’6" human reacting to something sharp he/she stepped on would be 33.3 ms [ 2(5.5/330) ]. And in a 1" spider, this same situation would yield a reaction-time of 0.51 ms. However, the average human reaction time is about 250 ms.
The difference in reaction time has more to do with the complexity/simplicity of the organism’s brain, nervous system, and musculoskeletal system.
Oh, and it’s worth noting that they’re traveling electrochemically, that is to say, it’s an electrical signal that travels until it encounters a synaptic gap, a physical gap where neurotransmitters are released by one side and accepted by the other. Due to how frequent these are, it’s remarkable that the signal travels as fact as 330 ft/s. However, if it was purely an electrical signal, like in a wire, it’s be traveling close to the speed of light, and the organism’s size would be extremely negligible. 
At the other extreme, sponges have no nerves and react to stimuli using electrical signals.
Apparently, if you poke a sponge, it takes several seconds for it to react.
Unless you move that rolled up newspaper really slowly… then it can’t detect it’s moving closer… and splat!
It is my understanding that electricity travels down the wire at only about 1% of the speed of light. I don’t know if that is “close”, but in any case the time within an organism would still be negligible.
It depends on what you mean by “electricity traveling”, and also on what you mean by “down the wire” and by “the speed of light”, but in no event is the speed 1% of the speed of light. The speed of individual electrons in the wire depends on the current and the size of wire, but it’s typically a literal snail’s pace or slower. The speed of signals, however, is equal to the speed of light either in the material of the wire itself or in the surrounding insulation, which can be anywhere from about 1/3 of c (the speed of light in a vacuum) to just slightly less than c.
Well, the net movement of the electrons in the direction (or opposite direction, depending on whether you’re doing physics or chemistry)* of the current is quite slow, the total speed of the electrons is much faster. They’re banging around all over the place, slowly being pushed in (against) the direction of the current by the electric field. It’s the variations in the strength/direction of the electric field that travel down the material nearly at the speed of light and can be used to send signals. As noted, nerves don’t run the entire length of our body, and there is a chemical component that depends on dispersion of molecules in the synaptic gap that occurs between nerves, and this is significantly slower than the speed of light. The speed of the signal down a nerve is also slower since it doesn’t propagate in the same way that electricity propagates down a wire, using ion channels instead of a continuous space of free electrons that react immediately to the changing electric field.
*At least when I took chemistry, we were told that chemists follow the convention that current flows in the same direction that the electrons move, while physicists use the convention that current flows in the direction that the net positive charges move.
Sorry for the brief hijack – I just wanted to point out that, despite fears that the SDMB is in serious decline nowadays, there are still folks just now joining up – like surripere – who provide cogent, interesting, factual information, in true Cecil style.
What i want to know how does a flock of sparrows turn in unison? They look like they are connected, somehow.
This is going to be a very unscientific answer since I have limited knowledge of biology. I’d guess that insects having faster reaction times has something to do with the complexity of their “circuitry”, as mentioned by someone earlier. I write software for microprocessor level circuits sometimes, and obviously the fewer impediments along the way - the faster the item works. A circuit that is optimized to do just a few things is (usually) much faster at those few things than your home computer. This is why your DSLR can optimize images much faster than Photoshop. It is built to do just that, and fast. A fly is evolved to do a few things very well, and one of those is avoid predators.