Glossary
A practical guide to examining dead bees for diagnostic information about colony health problems. The pattern, timing, location, and physical condition of dead bees provide valuable clues about diseases, pesticide exposure, starvation, and environmental stressors affecting the colony.
Normal mortality: a healthy colony loses approximately 1,000 bees per day during active foraging season as old foragers reach the end of their 5-6 week lifespan. Finding a few dozen dead bees in front of the hive daily is normal. Concern begins when dead bee numbers dramatically exceed this baseline.
Sudden large die-off (hundreds to thousands of dead bees in 1-2 days): strongly suggests pesticide exposure. The bees will often appear freshly dead, may be twitching or crawling aimlessly, and there may be dead and dying foragers in the approach flight path. Contact your state apiary inspector and collect samples for testing.
Bees with deformed or crumpled wings: deformed wing virus, transmitted by varroa mites. Bees with distended abdomens crawling on the ground: possibly Nosema or other gut pathogen. Bees with their tongues extended (proboscis extended reflex): often pesticide poisoning. Bees with missing or worn wing margins: natural aging in long-lived winter bees.
Examining individual dead bees under magnification can reveal varroa mites on the body (reddish-brown dots on the thorax or abdomen), tracheal mite damage (cut open the first thoracic segment and examine tracheal tubes for darkening), and signs of bacterial disease (ropy brown larval remains in brood cells, foul smell).
During active foraging season, a few dozen dead bees per day is normal (old foragers dying of natural causes). During winter, finding some dead bees on cleansing flights is normal. Hundreds of dead bees in a single day is abnormal and warrants investigation.
Bees that die with their proboscis (tongue) extended often indicate acute pesticide poisoning. The extended tongue is a reflex response that occurs during the neurotoxic effects of many insecticides. If you see this pattern, especially in large numbers, contact your state apiary inspector.
Yes, if you suspect pesticide exposure or disease. The USDA Bee Research Laboratory in Beltsville, Maryland accepts samples for disease analysis. For pesticide testing, contact your state department of agriculture. Collect at least 100 freshly dead bees in a sealed container and freeze until shipping.
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