Fixes #12838 - spiders getting stuck in zero-g despite being on webs

code/modules/mob/living/simple_animal/hostile/giant_spider.dm

@@ -47,6 +47,14 @@
 		if(C.can_inject(null, FALSE, inject_target, FALSE))
 			C.reagents.add_reagent("spidertoxin", venom_per_bite)
 
+/mob/living/simple_animal/hostile/poison/giant_spider/get_spacemove_backup()
+	. = ..()
+	// If we don't find any normal thing to use, attempt to use any nearby spider structure instead.
+	if(!.)
+		for(var/obj/structure/spider/S in range(1, get_turf(src)))
+			. = S
+			break
+
 //nursemaids - these create webs and eggs
 /mob/living/simple_animal/hostile/poison/giant_spider/nurse
 	desc = "Furry and black, it makes you shudder to look at it. This one has brilliant green eyes."

code/modules/mob/living/simple_animal/hostile/terror_spiders/terror_spiders.dm

@@ -391,6 +391,14 @@ GLOBAL_LIST_EMPTY(ts_spiderling_list)
 		return TRUE
 
 
+/mob/living/simple_animal/hostile/poison/terror_spider/get_spacemove_backup()
+	. = ..()
+	// If we don't find any normal thing to use, attempt to use any nearby spider structure instead.
+	if(!.)
+		for(var/obj/structure/spider/S in range(1, get_turf(src)))
+			. = S
+			break
+
 /mob/living/simple_animal/hostile/poison/terror_spider/Stat()
 	..()
 	// Determines what shows in the "Status" tab for player-controlled spiders. Used to help players understand spider health regeneration mechanics.