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apisanitas.HONEY BEE HEALTH
Poisoning

Pesticide poisoning

Severity : High Spring and summer, when crops are sprayedReview in progress
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Key points

  • Warning sign: many dead or trembling bees outside several hives at the same time.
  • Act fast: photos, date, treated crops nearby, a bee sample in the freezer.
  • Report the mortality to the veterinary authorities, who can arrange testing.
  • Chronic, low-dose poisoning is quieter but real.

Bees forage several kilometres around the apiary. They can therefore bring back residues of products applied to crops, gardens or roadsides.

Acute poisoning

It occurs within hours or days of heavy exposure.

  • A carpet of dead or dying bees outside the hive, often affecting several colonies at once.
  • Trembling, paralysed bees spinning on the spot, tongues extended.
  • Foragers that do not return: the colony loses its older bees.
  • Sometimes dead brood, when contaminated pollen has been fed to larvae.
Photo needed — Several hives in the same apiary with dead bees on the landing boards on the same day.

Chronic poisoning

At repeated low doses, effects are subtler: disoriented foragers, slower development, poorer queens, colonies more vulnerable to disease. These sublethal effects are now considered in European risk assessment1, 2.

Do not confuse with

Viral paralysis also causes trembling bees. The difference often lies in the timing: poisoning hits several colonies suddenly, in connection with a nearby treatment.

What to do

  1. Photograph the hives, the dead bees and the flowering crops nearby, with the date.
  2. Collect a few hundred dying or freshly dead bees in a clean bag and freeze them at once.
  3. Report the mortality to the veterinary authorities, who can arrange sampling and analysis.
  4. Record any spraying you saw and, if possible, identify the farm or area.
  5. Provide clean water and, if needed, feed the weakened colony.

Prevention

  • Know the crops within 3 km of your apiaries.
  • Talk to neighbouring farmers so you are warned before spraying.
  • If spraying is announced, temporarily close or move hives where possible.
  • Use hive veterinary products strictly according to the label3.

References

  1. EFSA (2013). Guidance on the risk assessment of plant protection products on bees (Apis mellifera, Bombus spp. and solitary bees). EFSA Journal 11(7): 3295.
  2. EFSA (2023). Revised guidance on the risk assessment of plant protection products on bees. EFSA Journal 21(5): 7989.
  3. FAO, IZSLT, Apimondia, CAAS (2021). Good beekeeping practices for sustainable apiculture. FAO Animal Production and Health Guidelines No. 25.

Updated : October 8, 2026
Written by : Apisanitas editorial team
Reviewed by : Review in progress