You can catch spiders in Animal Crossing: New Horizons all year long. The best time is from 7 PM to 8 AM.
If you know where they spawn and how to handle tree shaking safely, you can add one to your critter list without wasting time.

Check trees at night, keep your net ready, and move fast when a spider drops. Spiders sell for 600 Bells, so they are handy for museum progress or quick cash, as noted by Game8.
Spider Availability And Active Hours

Spiders are available on your island all year in both hemispheres. You do not need to wait for a special month.
Your best catching window is at night. The spawn rules have stayed consistent through the 3.0 update.
What Time Spiders Appear
You can catch spiders from 7 PM to 8 AM. That gives you a long night-time window, making them easy to hunt after sunset or before the morning reset, according to Game8’s spider guide.
Do Seasons Or Hemispheres Change Availability
Your hemisphere does not change spider availability. Spiders appear all year round in both the Northern and Southern Hemispheres.
The only real limit is the time of day.
Where To Find Them On Your Island

Focus on trees, since spiders spawn from them instead of wandering around on the ground. Cedar trees matter here too, and it helps to know the common lookalikes you might shake loose while searching.
Which Trees Can Spawn A Spider
Spiders can appear inside trees. Shake any regular tree or cedar tree you want to test.
A single shake is enough to check a tree, which saves time when you are sweeping an area.
What You Might Find Instead
Not every shake gives you a spider. You might get a bagworm, a wasp, furniture, or fruit instead, so keep your net ready and stay alert after each shake.
Catching One Without Missing

Good timing matters more than speed here. If you stay calm, watch the drop point, and keep enough space for your net swing, you can catch spiders without much trouble.
Shake Trees The Right Way
Stand close enough to a tree to shake it, then keep your net equipped. Since spiders can drop out right after the shake, you want to be ready before you start testing trees.
What To Do If The Spider Drops Away From You
If the spider lands a little far from you, move into position first instead of swinging too early. Line up your character and wait for a clean strike.
How To Catch A Spider In Animal Crossing
To catch a spider, equip your net, shake a tree, then press the swing button when the spider appears. This routine works best when you stay patient and avoid frantic movement.
What To Do After You Catch One

After you catch a spider, you can donate it, sell it, or hold it for a better price later. Your choice depends on whether you care more about filling the museum or making Bells.
Museum Donation Or Quick Sale
If you have not donated one yet, Blathers will take it for the museum. If you already have one on record, you can sell a spider for 600 Bells, which makes it a decent quick win when you want fast money, according to Game8.
Is It Worth Waiting For Flick
Yes, if you want more Bells, waiting for Flick can be smart. He pays more for bugs than the normal shop price.
A spider can be worth saving until he visits your island.