diff --git a/distributed/collections.py b/distributed/collections.py
index ebe26053858..34a0ff097f9 100644
--- a/distributed/collections.py
+++ b/distributed/collections.py
@@ -4,7 +4,7 @@
 import itertools
 import weakref
 from collections import OrderedDict, UserDict
-from collections.abc import Callable, Hashable, Iterator, MutableSet
+from collections.abc import Callable, Hashable, Iterable, Iterator, Mapping, MutableSet
 from typing import Any, TypeVar, cast
 
 T = TypeVar("T", bound=Hashable)
@@ -198,3 +198,17 @@ def clear(self) -> None:
         self._data.clear()
         self._heap.clear()
         self._sorted = True
+
+
+def sum_mappings(ds: Iterable[Mapping[K, V] | Iterable[tuple[K, V]]], /) -> dict[K, V]:
+    """Sum the values of the given mappings, key by key"""
+    out: dict[K, V] = {}
+    for d in ds:
+        if isinstance(d, Mapping):
+            d = d.items()
+        for k, v in d:
+            try:
+                out[k] += v  # type: ignore
+            except KeyError:
+                out[k] = v
+    return out
diff --git a/distributed/spans.py b/distributed/spans.py
index 49a8e7f5b2a..d85d52b1533 100644
--- a/distributed/spans.py
+++ b/distributed/spans.py
@@ -9,6 +9,7 @@
 
 import dask.config
 
+from distributed.collections import sum_mappings
 from distributed.metrics import time
 
 if TYPE_CHECKING:
@@ -199,7 +200,7 @@ def stop(self) -> float:
         return max(tg.stop for tg in self.traverse_groups())
 
     @property
-    def states(self) -> defaultdict[TaskStateState, int]:
+    def states(self) -> dict[TaskStateState, int]:
         """The number of tasks currently in each state in this span tree;
         e.g. ``{"memory": 10, "processing": 3, "released": 4, ...}``.
 
@@ -207,11 +208,7 @@ def states(self) -> defaultdict[TaskStateState, int]:
         --------
         distributed.scheduler.TaskGroup.states
         """
-        out: defaultdict[TaskStateState, int] = defaultdict(int)
-        for tg in self.traverse_groups():
-            for state, count in tg.states.items():
-                out[state] += count
-        return out
+        return sum_mappings(tg.states for tg in self.traverse_groups())
 
     @property
     def done(self) -> bool:
@@ -230,7 +227,7 @@ def done(self) -> bool:
         return all(tg.done for tg in self.traverse_groups())
 
     @property
-    def all_durations(self) -> defaultdict[str, float]:
+    def all_durations(self) -> dict[str, float]:
         """Cumulative duration of all completed actions in this span tree, by action
 
         See also
@@ -238,11 +235,7 @@ def all_durations(self) -> defaultdict[str, float]:
         duration
         distributed.scheduler.TaskGroup.all_durations
         """
-        out: defaultdict[str, float] = defaultdict(float)
-        for tg in self.traverse_groups():
-            for action, nsec in tg.all_durations.items():
-                out[action] += nsec
-        return out
+        return sum_mappings(tg.all_durations for tg in self.traverse_groups())
 
     @property
     def duration(self) -> float:
@@ -266,7 +259,7 @@ def nbytes_total(self) -> int:
         return sum(tg.nbytes_total for tg in self.traverse_groups())
 
     @property
-    def cumulative_worker_metrics(self) -> defaultdict[tuple[Hashable, ...], float]:
+    def cumulative_worker_metrics(self) -> dict[tuple[Hashable, ...], float]:
         """Replica of Worker.digests_total and Scheduler.cumulative_worker_metrics, but
         only for the metrics that can be attributed to the current span tree.
         The span_id has been removed from the key.
@@ -276,11 +269,9 @@ def cumulative_worker_metrics(self) -> defaultdict[tuple[Hashable, ...], float]:
         but more may be added in the future with a different format; please test for
         ``k[0] == "execute"``.
         """
-        out: defaultdict[tuple[Hashable, ...], float] = defaultdict(float)
-        for child in self.traverse_spans():
-            for k, v in child._cumulative_worker_metrics.items():
-                out[k] += v
-        return out
+        return sum_mappings(
+            child._cumulative_worker_metrics for child in self.traverse_spans()
+        )
 
     @staticmethod
     def merge(*items: Span) -> Span:
@@ -471,6 +462,7 @@ def heartbeat(self) -> dict[tuple[Hashable, ...], float]:
         --------
         SpansSchedulerExtension.heartbeat
         Span.cumulative_worker_metrics
+        distributed.worker.Worker.get_metrics
         """
         out = self.digests_total_since_heartbeat
         self.digests_total_since_heartbeat = {}
diff --git a/distributed/tests/test_collections.py b/distributed/tests/test_collections.py
index 6db1811072d..ce3c3778734 100644
--- a/distributed/tests/test_collections.py
+++ b/distributed/tests/test_collections.py
@@ -4,10 +4,11 @@
 import operator
 import pickle
 import random
+from collections.abc import Mapping
 
 import pytest
 
-from distributed.collections import LRU, HeapSet
+from distributed.collections import LRU, HeapSet, sum_mappings
 
 
 def test_lru():
@@ -345,3 +346,32 @@ def test_heapset_sort_duplicate():
     heap.add(c1)
 
     assert list(heap.sorted()) == [c1, c2]
+
+
+class ReadOnlyMapping(Mapping):
+    def __init__(self, d: Mapping):
+        self.d = d
+
+    def __getitem__(self, item):
+        return self.d[item]
+
+    def __iter__(self):
+        return iter(self.d)
+
+    def __len__(self):
+        return len(self.d)
+
+
+def test_sum_mappings():
+    a = {"x": 1, "y": 1.2, "z": [3, 4]}
+    b = ReadOnlyMapping({"w": 7, "y": 3.4, "z": [5, 6]})
+    c = iter([("y", 0.2), ("y", -0.5)])
+    actual = sum_mappings(iter([a, b, c]))
+    assert isinstance(actual, dict)
+    assert actual == {"x": 1, "y": 4.3, "z": [3, 4, 5, 6], "w": 7}
+    assert isinstance(actual["x"], int)  # Not 1.0
+    assert list(actual) == ["x", "y", "z", "w"]
+
+    d = {"x0": 1, "x1": 2, "y0": 4}
+    actual = sum_mappings([((k[0], v) for k, v in d.items())])
+    assert actual == {"x": 3, "y": 4}