Tracking Spiders

I need a program to track spiders.

[ebgreen]

I have a Yahoo Store which logs just about everything, except if your website has been visited by a spider and if so, which one and for how long. Is there some sort of tracking software that will do this? Lastly, is there a good invisible tracker available?

[ralnikov]

I think it's impossible 'cause SE spiders never (almost never) requests additional resources such as images, JS or any other.
So to track SE sp. you has only 2 ways: use a server-side script which determines SE spider OR analyze web server logs.

[ebgreen]

Thanks, that was the answer I expected. Does anyone know of a reliable invisible tracker?