The suit count is spider's difficulty setting, and it is a steep one. One suit is a puzzle you will usually solve. Four suits is a game good players lose more often than they win. Nothing in the rules changes between them — what changes is whether the cards you have built up can move.
The one rule that does all the work
In spider you can always drop a single card onto a card one rank higher, of any suit. A black nine goes on a red ten and the game allows it.
But a sequence only moves as a unit if every card in it is the same suit. A nine, ten and jack of spades travel together. A nine of spades under a ten of hearts does not — you would have to move them one at a time, and there is usually nowhere to put the loose cards.
That is the entire difficulty curve. With one suit, every descending run is automatically a single-suit run, so anything you build can be picked up and moved somewhere better. With four suits, most of what you build is a mixed pile that is frozen where it sits. You are not playing a harder matching game; you are playing the same game with far less mobility.
One suit
Every card is a spade. Any run you assemble moves as a block, so a column is never truly stuck — you can almost always lift a sequence off whatever is underneath it and park it elsewhere.
This is the version to learn on, and it is a real puzzle rather than a formality: you can still bury a card you need under a run you cannot unload anywhere. But recovery is nearly always possible, and a deal you have made a mess of can usually be rebuilt.
Two suits
Spades and hearts. This is where spider becomes the game people mean.
Half of what you build is now mixed and immobile, so the order you assemble runs in starts to matter more than how fast you assemble them. The habit to build here is checking, before you drop a card, whether you are about to turn a movable run into a stuck one. A red ten landing on a black jack feels like progress and is often the move that loses the column.
Most players settle here, and it is the right default.
Four suits
All four suits, two of each in the 104 cards. Almost every run you build is mixed, so almost nothing moves once it is placed.
The game turns into column management. You are no longer trying to build long sequences — you are trying to keep columns short and keep at least one of them empty. An empty column is the only place a mixed pile can be taken apart, one card at a time, and without one you simply run out of legal moves with half the deck still face down.
Four-suit spider is lost far more often than it is won, by everyone. If a deal collapses, that is the normal outcome and not a verdict on your play.
How often can each one be won?
Spider has been studied far less than Klondike, and the published numbers are looser.
The Solvitaire project at the University of St Andrews — the same program behind the well-known Klondike figure of 81.9% — put four-suit spider at 98.487%, give or take 1.513%. The range is wide because 269 of the 10,000 deals they tried ran out of time before the solver could decide them; the authors expect nearly all of those to be winnable, and an earlier count by Alex Robinson puts the figure at 99.99%. Either way, these numbers are for thoughtful play, where every face-down card is known in advance. They say that almost every four-suit deal has a way through — not that you will find it with half the deck hidden.
The gap between that ceiling and real play is easiest to see on this site's own engine. We let the hint play 2,000 deals of each setting, start to finish, on its own. It finished 66.5% of one-suit deals, 0.9% of two-suit deals and not one of the 2,000 four-suit deals. That is not a solvability figure — it is how often one heuristic that looks two moves ahead happens to find a way through. The drop between the three is the clearest measure of what the suit count really costs you.
What changes in how you play
Three things get more important as the suit count rises, in this order.
Empty columns
At one suit they are convenient. At four suits they are the game. Never fill one without a reason you could explain out loud.
Reading before placing
At one suit a wrong drop costs a move. At four suits it can freeze a column for the rest of the deal.
Dealing from the stock
Every column has to hold at least one card before the game will deal a new row, which means an empty column is also something you spend every time you need new cards. At four suits that trade is the central tension of the whole game.
So which should you play?
If you have never played spider, start at one suit for a few deals — not to win, but to see how a run behaves when it can move. Then go to two suits and stay there until losing stops annoying you. Four suits is worth playing when you want the hard version and are at peace with the result.
You choose the suits at the top of Spider Solitaire. Switching starts a fresh deal, and your wins and best score carry across all three. If you want the rules first, they are in how to play spider solitaire, and the rest of the family is in all the solitaire games.