The bug
As of 18w43a, the first snapshot for 1.14, the spider half of a spider jockey no longer performs melee spider attacks on the player. This effectively downgrades the spider jockey's behavior to that of a slightly more mobile skeleton. Only after killing the skeleton does the spider begin attacking the player.
In 1.13.2 and lower, the spider would attack and the skeleton would shoot in tandem.
How to reproduce
/summon spider ~ ~ ~ {Passengers:[{id:skeleton,Attributes:[{Name:"generic.attack_damage",Base:0d}],ArmorItems:[{},{},{},{id:ice,Count:1b}]}]}Make sure it's dark, so the spider should be hostile. Enter survival mode and observe. The skeleton will try to attack you (it can't because its attack damage is zero). The spider will make no attempt to attack you. Giving the skeleton a bow will cause it to start shooting, but the spider still will not attack.
In previous versions, both mobs would attack.
Linked issues
is duplicated by 3
MC-148511
Spiders and cave spiders with a passenger won't attack players and iron golems
Resolved
MC-154493
Spiders can't see anything when they're mounted
Resolved
MC-260450
Mounting an entity with /ride and inflicting damage on another entity with /damage makes the vehicle target the attacker but not inflict damage until player dismounts
Resolved
relates to 2
Attachments
Comments 3
Not entirely sure if it fits, but just in case:
Back in 15w38, I noticed that if you summon a Witch with a Bat as passenger, then the Witch will pursue/"cuddle" with you, but it didn't attack/didn't throw any potions at you (made a video back in the day, in case it'd be of any interest, I could link it). In general it seems that having specific mobs as passengers can completely or partially "override a hostile's brain", so to speak.
In 1.17.1, as for Witches, they will attack you now, but there are a couple of exceptions again when a Hostile won't get aggro, even if you hit it in Survival Mode; e.g. summon (when it's dark) a Cave Spider with a Bee or Bat as passenger, and they will stay friendly and also not pursue you.
However, if you have a Pig as passenger of a Cave Spider, the Cave Spider will pursue you, then walk off again, then pursue and bump you again etc., but it can't seem to hurt/poison you for some reason.
Cave Spiders summoned with Marker as passenger will remain friendly as well, also even if you hit it in Survival.
^ Only a few tests, just wanted to mention that I know similar behaviour already from back when "riding" was changed to "Passengers" (~10/2015), in case this would help.
I only used minimum required commands, e.g.:
/summon cave_spider ~ ~ ~ {Passengers:[{id:"minecraft:pig"}]}
Can confirm.