Brood stress guide
Chilled Brood in Honey Bees
Last updated: 1 May 2026
Chilled brood happens when developing brood becomes too cold for too long. It is not an infectious disease in the same way as American foulbrood, European foulbrood, chalkbrood or sacbrood, but it can still cause visible brood loss and patchy brood patterns.
In the UK it is most often seen after cold snaps, poor spring weather, weak colonies, over-expanded brood nests, small nucs, badly timed inspections or hives with too much empty space. The key issue is that the colony cannot keep all developing brood within the correct temperature range.
This guide explains what chilled brood looks like, why it happens, how to reduce the risk and when similar signs should make you check for other brood problems.
Quick signs of chilled brood
- Dead or discoloured larvae after cold weather
- Patchy brood pattern
- Brood on the edge of the nest affected first
- Larvae looking dull, grey, sunken or dried
- Weak colony unable to cover all brood
- Dead larvae or pupae being removed by workers
The timing matters. If the problem appears shortly after a cold spell, a long inspection, a weak split or a sudden expansion of the brood nest, chilling becomes more likely.
What does chilled brood look like?
Chilled brood often appears around the outer edges of the brood nest, where nurse bees could not keep the brood warm enough. Larvae or pupae may look greyish, dull, sunken, dried or dead. Workers may start removing dead brood, so you may also see larvae or pupae on the floor or near the entrance.
The brood pattern can become patchy because some developing bees have failed while others continue normally. Unlike some infectious brood diseases, the affected area may match the shape of brood that was outside the cluster or poorly covered by bees.
What causes chilled brood?
- Sudden cold snaps after brood rearing has expanded
- Small or weak colonies trying to cover too much brood
- Too much empty space in the hive
- Long or disruptive inspections in cold weather
- Splits or nucs made too weak
- Poor hive condition, draughts or damp
Chilled brood is often a management and weather-related problem rather than a pathogen problem. A strong colony can usually keep brood warm, but a weak colony may struggle if the brood nest is too large, the weather changes quickly or the hive has been opened for too long.
Is chilled brood a disease?
Chilled brood is not a disease in the same way as foulbrood, chalkbrood or sacbrood. It is brood loss caused by temperature stress. However, because it can produce dead larvae and a patchy brood pattern, it can be mistaken for a disease at first glance.
If signs persist after the colony strengthens and weather improves, or if you see sunken perforated cappings, ropiness, a strong abnormal smell or unusual larval breakdown, compare the symptoms with the wider brood problems guide.
How to tell chilled brood from disease
Chilled brood is often linked to a clear trigger such as cold weather, a weak colony, excessive space, a recent split or a long inspection. It is often worse at the edge of the brood nest. Brood diseases may show more specific signs such as mummified larvae, sac-like larvae, ropiness, sunken cappings or abnormal smell.
What to do if you suspect chilled brood
- Reduce excess space so the colony can cover the brood area.
- Avoid long inspections during cold, windy or wet conditions.
- Check colony strength and whether there are enough bees to cover brood.
- Ensure the hive is dry and weatherproof.
- Support the colony with food if stores are low.
- Monitor the next brood cycle to see whether the pattern improves.
In many cases the best approach is to correct the stress factor and give the colony time. If new brood looks healthier in the next cycle, chilling was likely a temporary setback.
What not to do
- Do not keep weak colonies in too much space.
- Do not inspect brood for long in poor weather.
- Do not ignore similar signs if they persist after conditions improve.
- Do not assume all patchy brood is chilled brood.
Chilled Brood FAQ
Brood that has already died will not recover, but the colony can recover if the underlying cause is corrected and the queen continues laying healthy brood.
No. Chilled brood is not a notifiable disease. However, suspicious brood disease signs should still be checked carefully.
Yes, especially if the inspection is long, the weather is cold or windy, or the colony is too small to re-cover the brood quickly.
It can cause patchy brood and dead larvae, but foulbrood has more specific warning signs. If you see sunken perforated cappings, ropiness, abnormal smell or suspicious larval breakdown, seek bee inspector advice.
Image credits
Disease reference images on this page are courtesy of The Animal and Plant Health Agency (APHA), Crown Copyright.