Step 1 - Is it actually a spider?
Spiders (order Araneae) have two body sections (cephalothorax and abdomen), eight legs, and no antennae. Several other arachnids are frequently mistaken for spiders:
- Daddy long-legs / harvestmen (Opiliones): single fused body, no waist, no silk, no venom apparatus.
- Camel spiders (Solifugae): pincer-like chelicerae, no waist, fast runners.
- Ticks and mites: 4–8 legs depending on stage, no waist, sucking mouthparts.
Step 2 - Eye arrangement
Eye arrangement is taxonomically definitive - even more so than color or size. Get a flashlight and look closely. Most spiders have eight eyes; recluse spiders are one of very few exceptions.
| Eye count and arrangement | Likely family |
|---|---|
| 6 eyes in 3 pairs (dyads) | Sicariidae - recluse spiders |
| 8 eyes, two large 'headlights' in front | Salticidae - jumping spiders |
| 8 eyes in three rows (2-4-2) | Lycosidae - wolf spiders |
| 8 eyes in two rows of 4, roughly equal | Theridiidae (widows, house spiders), Agelenidae (funnel weavers) |
| 8 eyes in tight cluster | Pholcidae - cellar spiders |
Step 3 - Web type
What the web looks like is one of the fastest narrowing tools, if a web is present.
| Web | Family clue |
|---|---|
| Classic flat orb wheel outdoors | Araneidae - orb weavers |
| Three-dimensional tangle close to ground, sticky gumfoot threads | Theridiidae - widows and house spiders |
| Sheet web with tunnel/funnel retreat at one end | Agelenidae - funnel weavers (incl. hobo, grass spiders) |
| Messy ceiling-corner tangle, owner hangs upside down | Pholcidae - cellar spiders |
| No web for prey capture; small silk retreat sac | Cheiracanthiidae (yellow sac), Sicariidae (recluse) |
| No web, active hunter on ground | Lycosidae (wolf), Salticidae (jumping) |
Step 4 - Body shape and size
Compare against a familiar reference. A U.S. quarter is about 25 mm across. Brown recluses with legs span roughly that - anything dramatically larger is something else.
| Species | Female body (mm) | Leg span (mm) |
|---|---|---|
| Brown Recluse | 7–12 | 20–30 |
| Southern Black Widow | 8–13 | 25–38 |
| Western Black Widow | 8–16 | 25–40 |
| Brown Widow | 7–12 | 20–35 |
| Hobo Spider | 11–15 | 27–45 |
| Yellow Sac Spider | 5–10 | 16–25 |
| Joro Spider | 17–25 | 60–100 |
| Northern Black Widow | 9–11 | 25–38 |
| Red Widow | 9–13 | 25–38 |
| Common House Spider | 5–8 | 20–30 |
| Wolf Spider | 10–35 | 25–80 |
| Cellar Spider | 7–10 | 40–70 |
| Bold Jumping Spider | 8–15 | 12–22 |
| Yellow Garden Spider | 19–28 | 50–75 |
| Golden Silk Orb Weaver | 22–40 | 75–120 |
| Grass Spider | 10–20 | 25–45 |
| Southern House Spider | 13–19 | 40–50 |
| Giant House Spider | 11–18 | 45–100 |
| Chilean Recluse | 8–15 | 25–45 |
Step 5 - Where and when you found it
- Cardboard box, shoe, attic in the south-central U.S.: consider brown recluse.
- Outdoor woodpile, electrical box, shed: consider black or brown widow.
- Basement / window well in the Pacific Northwest: hobo spider or giant house spider.
- Wall/ceiling corner, indoors: cellar spider or yellow sac spider.
- Running across the floor at night, large and hairy: wolf spider.
- Large golden orb between trees, southeastern U.S., autumn: Joro spider or golden silk orb weaver.
Most commonly confused pairs
Narrow by a single trait
If one feature stands out, jump straight to a list of candidates that share it: