You can use it to get the black widow
If you are referring to the keycard in Poptropica Counterfeit Island, you use it to unlock a door in the secret lair, which can be found in the countryside. It is locked so you have to find a key.
get the orange keycard in the light bule door.
Grab the keycard he dropped and go to the museum. the assisatant currator has a gift for you...
No there is not a spider.
nowhere
It opens the door to the treasure room of the Black Widow, who you will encounter soon enough. Go back to the museum and you will get a message from Early Poptropica.
just walk past it to the right corner and get the pig
You've just got to jump over the spider, or try and avoid it.
It open the Black Widow's secret treasure trove in her lair. You don't use it when you find it. Return to the museum where a package is waiting for you.
The spider key card is dropped by the shady guy after the scooter chase. It is used later, after you return to the museum and get a message from Early Poptropica.
Once you have gotten the keycard after the scooter chase you go to the art museum on early poptropica island and this lady will give you a key that goes to the cottage on the countryside.
You can get it from the person in the case in the Wharf that says "dont open until 2000" give him the coffee from Dr.Romero's coffee maker in the bunker and he will give it to you :)