diff --git a/2019/day24.py b/2019/day24.py
index f260689..240b3ae 100644
--- a/2019/day24.py
+++ b/2019/day24.py
@@ -1,3 +1,5 @@
+from collections import defaultdict
+
 from grid import Grid
 
 
@@ -7,13 +9,13 @@ DIM = 5
 def main():
     with open("day24.txt", "rt") as input_file:
         lines = input_file.readlines()
+
+    # Part 1
+    print("Part 1.")
     eris = Eris(value_factory=str, lines=lines)
     eris.dumb_print()
-    print()
-
     snapshots = []
     while True:
-        eris.dumb_print()
         eris.step()
         ss = eris.snapshot()
         if ss in snapshots:
@@ -22,6 +24,14 @@ def main():
     biorate = sum(2 ** i for i in range(DIM ** 2) if ss[i] == "#")
     print(f"Biodiv rate of first repeated layout: {biorate}.")
 
+    # Part 2
+    print("Part 2.")
+    reris = RecursiveEris(lines)
+    reris.levels[0].dumb_print()
+    for i in range(200):
+        reris.step()
+    print(f"{reris.count_bugs()} bugs found.")
+
 
 class Eris(Grid):
 
@@ -46,5 +56,83 @@ class Eris(Grid):
         return [self.getv(x, y) for y in range(DIM) for x in range(DIM)]
 
 
+class RecursiveEris:
+
+    def __init__(self, lines):
+        self.levels = defaultdict(lambda: Grid(value_factory=lambda: "."))
+        self.levels[0] = Grid(value_factory=lambda: ".", lines=lines)
+        self.levels[1] = Grid(value_factory=lambda: ".")
+        self.levels[-1] = Grid(value_factory=lambda: ".")
+
+    def step(self):
+        dying = []
+        infesting = []
+        for level_id in list(self.levels):
+            level_dying, level_infesting = self.step_level(level_id)
+            dying += level_dying
+            infesting += level_infesting
+        for p in dying:
+            self.levels[p[0]].setv(p[1], p[2], ".")
+        for p in infesting:
+            self.levels[p[0]].setv(p[1], p[2], "#")
+
+    def step_level(self, level_id):
+        level_dying = []
+        level_infesting = []
+        for y in range(DIM ** 2):
+            x = y % DIM
+            y //= DIM
+            if (x, y) == (2, 2):
+                continue
+            v = self.levels[level_id].getv(x, y)
+            num_nears = sum(n == "#" for n in self.somewhat_near_objects(level_id, x, y).values())
+            if v == "#" and num_nears != 1:
+                level_dying.append((level_id, x, y))
+            elif v == "." and num_nears in (1, 2):
+                level_infesting.append((level_id, x, y))
+        return level_dying, level_infesting
+
+    def somewhat_near_objects(self, level_id, x, y):
+        assert x in range(DIM) and y in range(DIM)
+        current_level = self.levels[level_id]
+        near_objs = {
+            (level_id, x    , y - 1): current_level.getv(x    , y - 1),
+            (level_id, x + 1, y    ): current_level.getv(x + 1, y    ),
+            (level_id, x    , y + 1): current_level.getv(x    , y + 1),
+            (level_id, x - 1, y    ): current_level.getv(x - 1, y    ),
+        }
+        for o in list(near_objs.keys()):
+            ol, ox, oy = o
+            # For outer level, just replace OOB pos with outer level tile value.
+            lower_level = self.levels[ol - 1]
+            if ox == -1:  # rightmost
+                near_objs[(ol - 1, 1, 2)] = lower_level.getv(1, 2)
+            elif ox == DIM:  # leftmost
+                near_objs[(ol - 1, 3, 2)] = lower_level.getv(3, 2)
+            if oy == -1:  # upmost
+                near_objs[(ol - 1, 2, 1)] = lower_level.getv(2, 1)
+            elif oy == DIM:  # downmost
+                near_objs[(ol - 1, 2, 3)] = lower_level.getv(2, 3)
+            # For inner level
+            if o == (level_id, 2, 2):
+                upper_level = self.levels[ol + 1]
+                del near_objs[o]
+                if x == 1:  # from the left
+                    near_objs.update({(ol + 1, 0, iy): upper_level.getv(0, iy) for iy in range(DIM)})
+                elif x == 3:  # from the right
+                    near_objs.update({(ol + 1, DIM - 1, iy): upper_level.getv(DIM - 1, iy) for iy in range(DIM)})
+                elif y == 1:  # from above
+                    near_objs.update({(ol + 1, ix, 0): upper_level.getv(ix, 0) for ix in range(DIM)})
+                else:  # y == 3, from below
+                    near_objs.update({(ol + 1, ix, DIM - 1): upper_level.getv(ix, DIM - 1) for ix in range(DIM)})
+        return near_objs
+    
+    def count_bugs(self):
+        return sum(self.count_bugs_in(level_id) for level_id in self.levels)
+    
+    def count_bugs_in(self, level_id):
+        return sum(v == "#" for _, _, v in self.levels[level_id].values_gen())
+
+
 if __name__ == "__main__":
     main()