Glossary
A beehive floor constructed with a wire mesh screen (typically 8-mesh hardware cloth) instead of a solid wooden floor. Screened bottom boards serve dual purposes: they allow varroa mites that lose their grip on bees to fall through the screen and out of the hive (preventing re-attachment), and they provide improved ventilation for heat and moisture management.
A key advantage of screened bottom boards is the ability to monitor mite levels through natural mite fall counts. A sticky board (corrugated plastic coated with petroleum jelly or cooking spray) placed beneath the screen catches falling mites. Counting the mites over a 3-day period and dividing by 3 gives a daily natural mite drop that correlates with the colony's infestation level.
Research suggests natural mite fall rates above 10-15 mites per day in summer indicate mite levels that require treatment. While alcohol wash and sugar roll tests are more accurate for determining mite percentage, sticky board monitoring provides continuous, non-invasive assessment without opening the hive.
The open mesh floor allows warm, moist air to exit from beneath the cluster (heat rises, and the lowest point of the hive functions as an exhaust in warm weather). In hot climates like Florida, screened bottoms significantly improve summer ventilation, reducing heat stress and moisture problems.
In cold climates, the open bottom can be covered (with a removable insert board) during winter to reduce cold drafts. The flexibility of removable inserts allows beekeepers to adjust ventilation seasonally: open in summer for maximum airflow, partially or fully closed in winter for warmth retention.
Screen bottom boards alone reduce mite populations by approximately 10-15 percent (mites that fall through cannot crawl back up). This is helpful but insufficient as a standalone varroa management strategy. They are best used as a monitoring tool within an integrated pest management program.
In cold climates (temperatures regularly below 20 degrees Fahrenheit), inserting a solid board beneath the screen reduces cold drafts. In mild climates like Florida, screened bottoms can remain open year-round. In moderate climates, inserting the board during the coldest months and removing it in spring is common practice.
Standard 8-mesh hardware cloth (8 squares per inch) is universally used. This mesh size allows varroa mites (1.1-1.6mm) to fall through while preventing bees from passing through or getting stuck. Finer mesh can clog with debris and restrict airflow.
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