Add near/vis checks, log on event spawn failure

code/modules/events/alien_infestation.dm

@@ -11,6 +11,10 @@
 /datum/event/alien_infestation/announce()
 	if(successSpawn)
 		GLOB.event_announcement.Announce("Unidentified lifesigns detected coming aboard [station_name()]. Secure any exterior access, including ducting and ventilation.", "Lifesign Alert", new_sound = 'sound/AI/aliens.ogg')
+	else
+		var/text = "Warning: Could not spawn any mobs for event Alien Infestation"
+		message_admins(text)
+		log_adminwarn(text)
 
 /datum/event/alien_infestation/start()
 	var/list/vents = get_valid_vent_spawns()

code/modules/events/blob.dm

@@ -6,6 +6,10 @@
 /datum/event/blob/announce()
 	if(successSpawn)
 		GLOB.event_announcement.Announce("Confirmed outbreak of level 5 biohazard aboard [station_name()]. All personnel must contain the outbreak.", "Biohazard Alert", 'sound/AI/outbreak5.ogg')
+	else
+		var/text = "Warning: Could not spawn any mobs for event Blob"
+		message_admins(text)
+		log_adminwarn(text)
 
 /datum/event/blob/start()
 	processing = FALSE //so it won't fire again in next tick

code/modules/events/spider_infestation.dm

@@ -13,6 +13,10 @@ GLOBAL_VAR_INIT(sent_spiders_to_station, 0)
 /datum/event/spider_infestation/announce()
 	if(successSpawn)
 		GLOB.event_announcement.Announce("Unidentified lifesigns detected coming aboard [station_name()]. Secure any exterior access, including ducting and ventilation.", "Lifesign Alert", new_sound = 'sound/AI/aliens.ogg')
+	else
+		var/text = "Warning: Could not spawn any mobs for event Spider Infestation"
+		message_admins(text)
+		log_adminwarn(text)
 
 /datum/event/spider_infestation/start()
 	var/list/vents = get_valid_vent_spawns()

code/modules/events/spider_terror.dm

@@ -11,9 +11,13 @@
 /datum/event/spider_terror/announce()
 	if(successSpawn)
 		GLOB.command_announcement.Announce("Confirmed outbreak of level 3 biohazard aboard [station_name()]. All personnel must contain the outbreak.", "Biohazard Alert", 'sound/effects/siren-spooky.ogg')
+	else
+		var/text = "Warning: Could not spawn any mobs for event Terror Spiders"
+		message_admins(text)
+		log_adminwarn(text)
 
 /datum/event/spider_terror/start()
-	var/list/vents = get_valid_vent_spawns()
+	var/list/vents = get_valid_vent_spawns(exclude_visible_by_mobs = TRUE)
 	var/spider_type
 	var/infestation_type = pick(1, 2, 3, 4, 5)
 	switch(infestation_type)
@@ -33,18 +37,8 @@
 			spider_type = /mob/living/simple_animal/hostile/poison/terror_spider/princess
 			spawncount = 2
 	while(spawncount && length(vents))
-		var/obj/vent = pick(vents)
-		// If the vent we picked has any living mob nearby, just remove it from the list, loop again, and pick something else.
-		var/turf/T = get_turf(vent)
-		var/hostiles_present = FALSE
-		for(var/mob/living/L in viewers(T))
-			if(L.stat != DEAD)
-				hostiles_present = TRUE
-				break
-
-		vents -= vent
-		if(!hostiles_present)
-			new spider_type(vent.loc)
-			spawncount--
-			successSpawn = TRUE
+		var/obj/vent = pick_n_take(vents)
+		new spider_type(vent.loc)
+		spawncount--
+		successSpawn = TRUE