diff --git a/ApiCore-Backend/src/queens/queens.service.spec.ts b/ApiCore-Backend/src/queens/queens.service.spec.ts
index 2c7f6eb..357f633 100644
--- a/ApiCore-Backend/src/queens/queens.service.spec.ts
+++ b/ApiCore-Backend/src/queens/queens.service.spec.ts
@@ -8,8 +8,9 @@ import { CalendarSyncService } from '../calendar-sync/calendar-sync.service';
 describe('QueensService', () => {
   let service: QueensService;
   let tx: {
+    queen: { update: jest.Mock };
     queenColonyHistory: { updateMany: jest.Mock; create: jest.Mock };
-    colony: { update: jest.Mock };
+    colony: { findUnique: jest.Mock; update: jest.Mock };
   };
   let prisma: {
     queen: {
@@ -30,8 +31,12 @@ describe('QueensService', () => {
 
   beforeEach(() => {
     tx = {
+      queen: { update: jest.fn().mockResolvedValue(queen) },
       queenColonyHistory: { updateMany: jest.fn(), create: jest.fn() },
-      colony: { update: jest.fn() },
+      colony: {
+        findUnique: jest.fn().mockResolvedValue(null),
+        update: jest.fn(),
+      },
     };
     prisma = {
       queen: {
@@ -163,6 +168,64 @@ describe('QueensService', () => {
     expect(prisma.queen.update).not.toHaveBeenCalled();
   });
 
+  describe('when a queen becomes unavailable', () => {
+    it('clears currentQueenId and marks the colony QUEENLESS', async () => {
+      prisma.queen.findUnique.mockResolvedValue(queen);
+      tx.colony.findUnique.mockResolvedValue({
+        id: 'colony-1',
+        status: 'ACTIVE',
+      });
+
+      await service.update('queen-1', { status: 'DECEASED' }, 'user-1');
+
+      expect(tx.colony.update).toHaveBeenCalledWith({
+        where: { id: 'colony-1' },
+        data: { currentQueenId: null, status: 'QUEENLESS' },
+      });
+      const [[closeArg]] = tx.queenColonyHistory.updateMany.mock.calls as [
+        [{ where: { queenId: string; colonyId: string; endDate: null } }],
+      ];
+      expect(closeArg.where).toEqual({
+        queenId: 'queen-1',
+        colonyId: 'colony-1',
+        endDate: null,
+      });
+    });
+
+    it('clears currentQueenId but leaves an already-terminal colony status alone', async () => {
+      prisma.queen.findUnique.mockResolvedValue(queen);
+      tx.colony.findUnique.mockResolvedValue({
+        id: 'colony-1',
+        status: 'DISSOLVED',
+      });
+
+      await service.update('queen-1', { status: 'LOST' }, 'user-1');
+
+      expect(tx.colony.update).toHaveBeenCalledWith({
+        where: { id: 'colony-1' },
+        data: { currentQueenId: null, status: undefined },
+      });
+    });
+
+    it('does nothing when the queen is not currently assigned to a colony', async () => {
+      prisma.queen.findUnique.mockResolvedValue(queen);
+      tx.colony.findUnique.mockResolvedValue(null);
+
+      await service.update('queen-1', { status: 'SOLD' }, 'user-1');
+
+      expect(tx.colony.update).not.toHaveBeenCalled();
+    });
+
+    it('does not touch the colony for a status change that keeps the queen available', async () => {
+      prisma.queen.findUnique.mockResolvedValue(queen);
+
+      await service.update('queen-1', { status: 'RESERVE' }, 'user-1');
+
+      expect(tx.colony.findUnique).not.toHaveBeenCalled();
+      expect(tx.colony.update).not.toHaveBeenCalled();
+    });
+  });
+
   it('getLineage builds the ancestor chain and the descendant tree', async () => {
     const grandmother = {
       id: 'queen-gm',
diff --git a/ApiCore-Backend/src/queens/queens.service.ts b/ApiCore-Backend/src/queens/queens.service.ts
index 2a89967..1fe5c07 100644
--- a/ApiCore-Backend/src/queens/queens.service.ts
+++ b/ApiCore-Backend/src/queens/queens.service.ts
@@ -40,6 +40,19 @@ export interface QueenLineage {
 
 const MAX_LINEAGE_DEPTH = 8;
 
+// Once a queen reaches one of these statuses she is no longer really "in"
+// whatever colony currently points at her - a colony's currentQueenId and
+// status would otherwise silently go stale (still showing a dead/lost
+// queen as current, never flagged QUEENLESS) until someone happens to
+// notice and fix it by hand.
+const QUEEN_NO_LONGER_AVAILABLE_STATUSES: QueenStatus[] = [
+  'LOST',
+  'DECEASED',
+  'REPLACED',
+  'SOLD',
+];
+const TERMINAL_COLONY_STATUSES = ['DISSOLVED', 'SOLD', 'DECEASED', 'MERGED'];
+
 @Injectable()
 export class QueensService {
   constructor(
@@ -92,9 +105,37 @@ export class QueensService {
       }
       await this.assertMotherQueenExists(dto.motherQueenId);
     }
-    const queen = await this.prisma.queen.update({
-      where: { id },
-      data: { ...dto },
+    const becameUnavailable =
+      dto.status !== undefined &&
+      dto.status !== before.status &&
+      QUEEN_NO_LONGER_AVAILABLE_STATUSES.includes(dto.status);
+
+    const queen = await this.prisma.$transaction(async (tx) => {
+      const updated = await tx.queen.update({
+        where: { id },
+        data: { ...dto },
+      });
+      if (becameUnavailable) {
+        const colony = await tx.colony.findUnique({
+          where: { currentQueenId: id },
+        });
+        if (colony) {
+          await tx.colony.update({
+            where: { id: colony.id },
+            data: {
+              currentQueenId: null,
+              status: TERMINAL_COLONY_STATUSES.includes(colony.status)
+                ? undefined
+                : 'QUEENLESS',
+            },
+          });
+          await tx.queenColonyHistory.updateMany({
+            where: { queenId: id, colonyId: colony.id, endDate: null },
+            data: { endDate: new Date() },
+          });
+        }
+      }
+      return updated;
     });
     await this.auditLog.record({
       entityType: 'Queen',