Bee counters record how many bees enter and leave. They form part of the sensor systems used to follow a colony without opening it.

How they work

A passage is fitted at the entrance with sensors registering passing bees. Some systems distinguish direction, others also whether a bee is carrying pollen.

What the data show

• The daily flight pattern and how it changes with weather and forage
• A sudden drop: An indication of poisoning, disease or predation pressure
• Loss of foragers not visible as dead bees in front of the hive
• Swarming as a sudden outflow

Where the real value lies

The sublethal effect of pesticides. A bee that cannot navigate does not return — she is not counted as a dead bee but she is gone.

A counter comparing departures with returns makes exactly that loss visible, which otherwise goes entirely unnoticed.

It is also useful under invasive hornet pressure: the greatest harm there is not the number of bees caught but that the colony stops flying.

The limits

• The passage hinders the bees; at busy times it creates congestion
• Clogging with propolis and debris
• Power and connectivity are the commonest failures in the field
• It tells you that something changed, not why

Relative to other sensors

If only one sensor is used, it should measure weight. That answers the question the eye cannot: there are flowers, but is there a flow?

A counter is a supplement, not a first choice.

The question to settle first

Decide before buying what decision the data will prompt. Collecting graphs is not making decisions.