When to put a mouse guard on a beehive
Mice go looking for a warm place to spend the winter in fall, and a hive full of comb and honey is one. The sources I opened agree on that and disagree on the date. This page lines up what each says about timing and about the size of the opening, then adds a short list for a hive that is still open in late October.
What the sources say about timing
| Source | Timing | Reason given |
|---|---|---|
| Cornell CALS, overwintering | "In the fall" | "In the fall, mice start looking for nice warm places to spend the winter." Guards go in the lower entrances. |
| Carolina Honeybees (supplier) | Late summer or early fall | Before cold weather arrives. It notes a fixed-hole guard can slow bee traffic during a honey flow. |
| Thomas Acres (supplier) | Late August to early September in most temperate climates | Mice move in once the colony stops defending the entrance. A guard fitted late can trap a mouse inside. |
| University of Florida, northern overwintering | No date | Entrance reducers or wired mouse guards are described as simple, easy defenses. Rodents can destroy comb and eat the honey. |
No source I opened gives a temperature trigger. Thomas Acres ties the date to the colony: the bees cluster and stop patrolling the entrance. Carolina Honeybees ties it to the coming cold, and adds that colder regions may need guards earlier.
How big the opening should be
Carolina Honeybees recommends an opening of about 3/8 inch (9.5 mm) for most hives, and says 1/2-inch hardware cloth can let small mice squeeze through. Thomas Acres gives about 10 mm and says a worker bee is under 9 mm across, while a mouse's skull will not pass through much under 12 to 13 mm. Cornell's advice is for a home-made guard: cut hardware cloth at least three times the height of the entrance, fold it in half and push it in.
| Measure | Inches | Millimeters | Who gives it |
|---|---|---|---|
| Worker bee width | under 0.354 | under 9 | Thomas Acres |
| Recommended opening | 0.375 (3/8) | 9.5 | Carolina Honeybees |
| Recommended opening | 0.4 | 10 | Thomas Acres |
| Opening a mouse skull needs to pass | 0.47 to 0.51 | 12 to 13 | Thomas Acres |
| Hardware cloth that may let small mice through | 0.5 (1/2) | 12.7 | Carolina Honeybees |
The table is a lookup from those pages. I have not measured anything myself, and the Florida publication gives no sizes.
Taking it off in spring
Carolina Honeybees says guards are generally removed as the weather warms and the colony gets busy, and to take them off before heavy foraging if your area has an early flow. Thomas Acres says early spring, because pollen foragers lose part of their loads squeezing through and cleansing flights back up behind a restricted entrance.
If you are reading this in late October
My suggestion: look at the entrance and the bottom board first. Droppings, chewed wax or a nest in the entrance mean a mouse may already be inside, and Thomas Acres warns that a guard fitted over it traps it with your comb. If the hive is clear, a guard now is better than none, since I think mice keep looking for shelter all through the cold months.
Do it on a day above 50°F (10°C). That is the line Cornell uses for wrapping, and the fall feeding cutoff works from similar temperatures. Check the hive's reserves while you are at the entrance: the hive weight page turns a lift or scale reading into pounds of honey.
Related fall tasks
- Insulation and wind: should I wrap my beehive for winter.
- Enough honey: the winter stores calculator.
- Mite count before the cluster forms: the varroa mite calculator.