diff --git a/superscore/backends/filestore.py b/superscore/backends/filestore.py
index 07e4348..7d317cd 100644
--- a/superscore/backends/filestore.py
+++ b/superscore/backends/filestore.py
@@ -8,7 +8,8 @@
 import os
 import shutil
 from dataclasses import fields, replace
-from typing import Any, Dict, Generator, Optional, Union
+from functools import cache
+from typing import Any, Container, Dict, Generator, Optional, Union
 from uuid import UUID, uuid4
 
 from apischema import deserialize, serialize
@@ -293,7 +294,7 @@ def search(self, *search_terms: SearchTermType) -> Generator[Entry, None, None]:
                     if attr == "entry_type":
                         conditions.append(isinstance(entry, target))
                     elif attr == "ancestor":
-                        conditions.append(self._is_ancestor(target, entry.uuid))
+                        conditions.append(entry.uuid in self._gather_progeny(target))
                     else:
                         try:
                             # check entry attribute by name
@@ -304,17 +305,25 @@ def search(self, *search_terms: SearchTermType) -> Generator[Entry, None, None]:
                 if all(conditions):
                     yield entry
 
-    def _is_ancestor(self, ancestor: UUID, entry: UUID):
+    @cache
+    def _gather_progeny(self, ancestor: UUID) -> Container[UUID]:
+        """
+        Finds all entries accessible from ancestor, and returns their UUIDs. This
+        makes it easy to check if one entry is hierarchically under another.
+
+        This method is cached to keep runtimes low when checking multiple entries
+        against the same ancestor.  To keep data valid, clear this method's cache
+        """
+        progeny = set()
         q = [ancestor]
         while len(q) > 0:
-            search_entry = q.pop()
-            if not isinstance(search_entry, Entry):
-                search_entry = self._entry_cache[search_entry]
-            if search_entry.uuid == entry:
-                return True
-            elif isinstance(search_entry, Nestable):
-                q.extend(search_entry.children)
-        return False
+            cur = q.pop()
+            if not isinstance(cur, Entry):
+                cur = self._entry_cache[cur]
+            progeny.add(cur.uuid)
+            if isinstance(cur, Nestable):
+                q.extend(cur.children)
+        return progeny
 
     @contextlib.contextmanager
     def _load_and_store_context(self) -> Generator[Dict[UUID, Any], None, None]:
diff --git a/superscore/tests/test_backend.py b/superscore/tests/test_backend.py
index 288c46f..066f70e 100644
--- a/superscore/tests/test_backend.py
+++ b/superscore/tests/test_backend.py
@@ -205,12 +205,11 @@ def test_update_entry(backends: _Backend):
 
 
 @pytest.mark.parametrize("filestore_backend", [("linac_data",)], indirect=True)
-def test_is_ancestor(filestore_backend: _Backend):
-    assert filestore_backend._is_ancestor(
-        UUID("06282731-33ea-4270-ba14-098872e627dc"),
-        UUID("927ef6cb-e45f-4175-aa5f-6c6eec1f3ae4")
-    )  # top-level snapshot
-    assert filestore_backend._is_ancestor(
-        UUID("2f709b4b-79da-4a8b-8693-eed2c389cb3a"),
-        UUID("927ef6cb-e45f-4175-aa5f-6c6eec1f3ae4")
-    )  # direct parent snapshot
+def test_gather_progeny(filestore_backend: _Backend):
+    # top-level snapshot
+    progeny = filestore_backend._gather_progeny(UUID("06282731-33ea-4270-ba14-098872e627dc"))
+    assert UUID("927ef6cb-e45f-4175-aa5f-6c6eec1f3ae4") in progeny
+
+    # direct parent snapshot
+    progeny = filestore_backend._gather_progeny(UUID("2f709b4b-79da-4a8b-8693-eed2c389cb3a"))
+    assert UUID("927ef6cb-e45f-4175-aa5f-6c6eec1f3ae4") in progeny