What is a "spider"?
 

I sometimes glance at who is online, and there is usually a "spider" present - specifically "MSNBot spider" or "Yahoo! slurp spider".

What exactly are these?

They are automated programs that load and scan webpages so they can index them for the various search engines. They also suck blood.

Got it. Thanks.

I typically refer to my mother in law as a "vampire", not a "spider", though.

Much like your typical right-wing conservative. :)

At the time of this posting there were 9 slurp spiders on LoT. Someone call Rid-A-Bug!
:D

I for one welcome our new spider overlords.

Nowhere near our previous record of 299.

Holy frijoles!
:D

Tell me, how can a search spider register? I looked at "Who's Online" just now and a Yahoo Slurp Spider was "Registering".
Weird.

It just means it browsed to the registration page. It won't be able to actually register.