What it usually means
Few animals produce a reaction as fast and as widely shared as a spider does. Fear of spiders is one of the most common specific fears, and a dream spider often arrives with that charge ready-made: small, sudden, too many legs, in the wrong place. A good number of spider dreams are simply that fear, released at night.
The other half is the web. A spider is the one common animal that builds a trap out of its own body, patiently, strand by strand. Dreams draw on both sides of that: being caught in something that was built slowly around you, and the work of making something intricate a little at a time.
So the first thing to settle is where you stood in relation to it. Watching a spider work is a different dream from walking into a web, and both are different from a spider on your skin. The distance between you and it is usually the distance between you and the problem.
What changes the meaning
Walking into a web. Being caught in something you did not see being built: an arrangement, an obligation, a situation that became sticky by degrees.
A spider on your body. Closeness to something unwelcome. The fear here is about contact — something has got too near.
A huge spider. Scale is emphasis. A small worry drawn at the size it feels, not the size it is.
Many spiders. Not one problem but a crowd of small ones. Often belongs to periods of scattered, low-level stress.
Watching a spider spin. The calmer version. Patience, craft, and the kind of work that only shows its shape at the end.
Killing a spider. Dealing decisively with an irritant, or overreacting to something small. Your mood on waking usually tells you which.
A spider in the house. Something unwelcome in private space. The room it appears in often narrows it down.
A spider that does not move. Waiting. Something is holding still until the right moment, and the dream is not sure whether that is you or someone else.
Being bitten. A small injury out of proportion to its size — a remark, a message, a moment that stung more than it should have.
When it keeps coming back
If you are afraid of spiders when awake, recurring spider dreams may need no further reading: frightening things turn up in dreams roughly in proportion to how frightening they are. Such dreams often ease when the waking fear eases, and fears of this kind respond well to gradual exposure.
If not, recurring spiders tend to follow situations that tighten slowly — a job, a family arrangement, a commitment that was small at the start. Watch the web across the dreams rather than the spider in any one of them. A web that grows, or a spider that comes a little closer each time, is the dream tracking something that has not stopped growing.
In Jungian terms
Jungian writers have read the spider as an image of fate and of the binding, weaving side of the Great Mother. In myth the thread of a life is spun, and a web is a spun thing; Arachne, turned into a spider for weaving too well, belongs to the same family of stories. The psychoanalyst Karl Abraham went further and read the dream spider as an overpowering mother, a reading that has stayed in the literature ever since.
Neither needs to be taken literally. What the tradition points to is that a web holds as well as traps, depending on who is inside it. A dream spider can be the part of you that makes careful, binding things — or a relationship whose threads have started to feel tight.
The plain form of the question is this. What has been woven around you slowly, and are you caught in the web or sitting at its centre.