On hard difficulty, spiders have up to a 10% chance (depending on regional difficulty) of spawning with a single beneficial status effect. This effect can be speed (40%), strength (20%), regeneration (20%) or invisibility (20%), and has an essentially infinite duration.

This was added in version 1.6.1 of Minecraft: Java Edition, and also had been in the console version before receiving the better together update, but in the pocket edition (now bedrock) it never happened.

Put the difficulty of the game in the difficult and spawn many spiders, in the current version, none will generate correctly with the buffs.