Scout bees from the strong colonies constantly probe neighbouring hives. Whenever a scout finds an entrance it can slip through unchallenged, it fills up on stolen honey, flies home and recruits nestmates back to the exact same spot — a positive feedback loop that can turn a handful of scouts into a full mass raid within hours. Guard bees stationed at the entrance intercept and reject intruders; how many guards a colony can field to cover a given entrance width determines whether that feedback loop runs away or fizzles out.
pressure P = entranceOpenness × (1 − guardCoverage)
guardCoverage = clamp(guards / (BASE × openness), 0, 1)
d(robbers)/dt = robbers × Krecruit × P − robbers × Kdecay × (1−P)
raidRate = robbers × P × enterRate
- Guard bees — more guards raise coverage of the entrance, directly suppressing the recruitment term.
- Wide open — full-width entrance; a small guard force is easily overwhelmed once the feedback loop starts compounding.
- Entrance reducer — narrows the physical opening so far fewer guards are needed to fully cover it.
- Robbing screen — forces bees through an offset, disorienting route; cuts effective raid throughput almost to zero even against a determined mass of robbers already recruited.
Real-world relevance: UK beekeepers fit entrance reducers or robbing screens to nucs and weak colonies as standard practice through the late-summer dearth, precisely because prevention — closing off the opportunity before the first successful scout gets home — is far easier than stopping an in-progress mass raid.