diff --git a/modules/wave_defense/main.lua b/modules/wave_defense/main.lua
index 035bb70c..22ca1b5f 100644
--- a/modules/wave_defense/main.lua
+++ b/modules/wave_defense/main.lua
@@ -132,6 +132,12 @@ local function spawn_unit_group()
 		if not biter then break end
 		unit_group.add_member(biter)
 	end
+	for i = 1, #global.wave_defense.unit_groups, 1 do
+		if not global.wave_defense.unit_groups[i] then
+			global.wave_defense.unit_groups[i] = unit_group
+			return true
+		end
+	end
 	global.wave_defense.unit_groups[#global.wave_defense.unit_groups + 1] = unit_group
 	return true
 end
@@ -328,7 +334,7 @@ local function on_tick()
 	
 	if game.tick > global.wave_defense.next_wave then	set_next_wave() end
 	
-	if game.tick % 180 == 0 then
+	if game.tick % 300 == 0 then
 		if game.tick % 1800 == 0 then
 			time_out_biters()
 		end
@@ -337,6 +343,8 @@ local function on_tick()
 		spawn_attack_groups()
 		set_unit_group_count()
 		give_commands_to_unit_groups()
+		build_nest()
+		build_worm()
 	end	
 end
 
@@ -365,7 +373,11 @@ function reset_wave_defense()
 		game_lost = false,
 		threat = 0,
 		simple_entity_shredding_count_modifier = 0.0003,
-		simple_entity_shredding_cost_modifier = 0.01,		--threat cost for one health
+		simple_entity_shredding_cost_modifier = 0.01,			--threat cost for one health
+		nest_building_density = 16,										--lower values = more dense building
+		nest_building_chance = 8,											--high value = less chance
+		worm_building_density = 16,									--lower values = more dense building
+		worm_building_chance = 8,										--high value = less chance
 	}
 end
 
diff --git a/modules/wave_defense/threat_events.lua b/modules/wave_defense/threat_events.lua
index 78f39785..ab6a69f5 100644
--- a/modules/wave_defense/threat_events.lua
+++ b/modules/wave_defense/threat_events.lua
@@ -1,6 +1,58 @@
 local threat_values = require "modules.wave_defense.threat_values"
 local math_random = math.random
 
+local function remove_unit(entity)
+	if not global.wave_defense.active_biters[entity.unit_number] then return end
+	global.wave_defense.active_biters[entity.unit_number] = nil
+	global.wave_defense.active_biter_count = global.wave_defense.active_biter_count - 1
+end
+
+function build_nest()
+	if global.wave_defense.threat < 1000 then return end
+	if math_random(1, global.wave_defense.nest_building_chance) ~= 1 then return end
+	local group = global.wave_defense.unit_groups[math_random(1, #global.wave_defense.unit_groups)]
+	if not group then return end
+	if not group.valid then return end
+	if not group.members then return end
+	if not group.members[1] then return end
+	local unit = group.members[math_random(1, #group.members)]
+	if not unit.valid then return end
+	local r = global.wave_defense.nest_building_density
+	if unit.surface.count_entities_filtered({type = "unit-spawner", area = {{unit.position.x - r, unit.position.y - r},{unit.position.x + r, unit.position.y + r}}}) > 0 then return end
+	local position = unit.surface.find_non_colliding_position("biter-spawner", unit.position, 5, 1)
+	if not position then return end
+	unit.surface.create_entity({name = "biter-spawner", position = position, force = unit.force})
+	unit.surface.create_entity({name = "blood-explosion-huge", position = position})
+	unit.surface.create_entity({name = "blood-explosion-huge", position = unit.position})
+	remove_unit(unit)
+	unit.destroy()
+	global.wave_defense.threat = global.wave_defense.threat - 500
+end
+
+function build_worm()
+	if global.wave_defense.threat < 1000 then return end
+	if math_random(1, global.wave_defense.worm_building_chance) ~= 1 then return end
+	local group = global.wave_defense.unit_groups[math_random(1, #global.wave_defense.unit_groups)]
+	if not group then return end
+	if not group.valid then return end
+	if not group.members then return end
+	if not group.members[1] then return end
+	local unit = group.members[math_random(1, #group.members)]
+	if not unit.valid then return end
+	local r = global.wave_defense.worm_building_density
+	if unit.surface.count_entities_filtered({type = "turret", area = {{unit.position.x - r, unit.position.y - r},{unit.position.x + r, unit.position.y + r}}}) > 0 then return end
+	wave_defense_set_worm_raffle(global.wave_defense.wave_number)
+	local worm = wave_defense_roll_worm_name()
+	local position = unit.surface.find_non_colliding_position(worm, unit.position, 5, 1)
+	if not position then return end
+	unit.surface.create_entity({name = worm, position = position, force = unit.force})
+	unit.surface.create_entity({name = "blood-explosion-huge", position = position})
+	unit.surface.create_entity({name = "blood-explosion-huge", position = unit.position})
+	remove_unit(unit)
+	unit.destroy()
+	global.wave_defense.threat = global.wave_defense.threat - threat_values[worm]
+end
+
 local function get_circle_vectors(radius)
 	local vectors = {}
 	for x = radius * -1, radius, 1 do
@@ -22,7 +74,7 @@ local acid_nova_entities = {
 
 local function acid_nova(entity)
 	if not acid_nova_entities[entity.name] then return end
-	if global.wave_defense.threat < 25000 then return end
+	if global.wave_defense.threat < 50000 then return end
 	if math_random(1, 16) ~= 1 then return end	
 	for _ = 1, acid_nova_entities[entity.name].amount, 1 do
 		local i = math_random(1, #acid_nova_entities[entity.name].vectors)		
@@ -40,12 +92,6 @@ local function acid_nova(entity)
 	return true
 end
 
-local function remove_unit(entity)
-	if not global.wave_defense.active_biters[entity.unit_number] then return end
-	global.wave_defense.active_biters[entity.unit_number] = nil
-	global.wave_defense.active_biter_count = global.wave_defense.active_biter_count - 1
-end
-
 local function create_particles(entity)
 	local particle = "stone-particle"
 	if entity.type == "tree" then particle = "branch-particle" end
diff --git a/modules/wave_defense/threat_values.lua b/modules/wave_defense/threat_values.lua
index 9a49abef..5e357323 100644
--- a/modules/wave_defense/threat_values.lua
+++ b/modules/wave_defense/threat_values.lua
@@ -7,8 +7,8 @@ return {
 	["medium-spitter"] = 4,
 	["small-biter"] = 1,
 	["small-spitter"] = 1,
-	["small-worm-turret"] = 16,		
-	["medium-worm-turret"] = 24,		
-	["big-worm-turret"] = 32,		
-	["behemoth-worm-turret"] = 48,
+	["small-worm-turret"] = 32,		
+	["medium-worm-turret"] = 48,		
+	["big-worm-turret"] = 64,		
+	["behemoth-worm-turret"] = 80,
 }
\ No newline at end of file