you cant see the fire on a spider when its on fire.
Linked issues
is duplicated by 4
MC-34028
Spiders and cave spider burn to death but don't show flames
Resolved
MC-35241
Spiders on fire don't show a fire animation
Resolved
MC-36470
Spiders hit by fire aspect swords would be ignited but fire would not be visible.
Resolved
MC-36500
Spiders do not get on fire when hit with fire aspect, instead their texture lights up ,but it still takes fire damage
Resolved
Can confirm.