Honey bee swarming is a spectacular natural event involving the mass movement of thousands of bees leaving their existing home. This phenomenon, which often occurs in late spring or early summer, can appear chaotic and alarming to an observer. Despite the dramatic scale of the activity, a swarm is not a sign of aggression; the bees are generally docile as they are focused on a single mission: finding a new nesting site. Swarming is a necessary, peaceful part of the honey bee life cycle that ensures the long-term survival of the species.
Swarming as Colony Reproduction
The primary biological function of swarming is the reproduction of the entire colony, which is the honey bee’s unique method of multiplication. The colony functions as a single, complex organism that reproduces by splitting itself into two distinct units. This process allows the bee population to expand and colonize new territories.
Swarm preparation begins when the hive decides the colony has grown large enough to divide. The existing queen is prepared for flight, and worker bees begin constructing specialized, peanut-shaped queen cells within the brood nest. These cells are provisioned and sealed, each containing a developing successor to the current queen.
When the old queen departs with the swarm, she leaves behind a viable colony containing nurse bees, developing brood, stored resources, and the newly developing queen cells. The original hive continues its functions, and once a new queen emerges, mates, and begins laying eggs, the cycle of growth resumes. The outcome of the split is the creation of two functional colonies from one, achieving colony-level reproduction.
Internal and Environmental Triggers
The decision to swarm is the result of several interconnected internal and environmental factors reaching a specific threshold.
Colony Congestion
One of the most significant internal triggers is colony congestion, which occurs when the hive population booms faster than the available space. This overcrowding causes poor ventilation and a lack of open cells for the queen to lay eggs, creating hive stress.
Pheromone Dilution
A second internal trigger involves the dilution of the Queen Mandibular Pheromone (QMP), a chemical signal produced by the queen that maintains colony cohesion. QMP is distributed throughout the hive by worker bees through physical contact and food sharing (trophallaxis). As the colony size increases, the pheromone is no longer effectively circulated to all corners of the hive, particularly to the younger bees. When the QMP level drops below a certain threshold, it signals that the queen’s influence is waning. This prompts workers to initiate the construction of queen cells, which is the clearest internal sign that a swarm is imminent.
Resource Availability
The main environmental factor that makes swarming possible is the availability of abundant resources, typically provided by the spring nectar flow. This influx of nectar and pollen ensures the colony has the necessary fuel and materials, primarily wax, to quickly build a new home and sustain itself through the initial establishment phase. A colony will rarely risk swarming when food is scarce, because the energy demands of founding a new nest are considerable. The interplay between high population density, reduced QMP distribution, and favorable weather conditions dictates the precise timing of the swarm.
The Swarm Journey: From Hive to Home
Preparation and Departure
Once the colony is committed to swarming, the old queen drastically reduces her egg-laying rate and is put on a restricted diet by workers. This allows her abdomen to shrink and her weight to decrease, making her capable of sustained flight. Before departure, the bees preparing to leave, which can be up to half of the adult worker population, gorge themselves on honey. Each bee may consume up to 35 milligrams of honey, storing the fuel necessary to power their journey and to secrete wax for building comb at the new location.
Temporary Clustering
The swarm issues from the hive in a roaring cloud, with the old queen at the center of the mass. This massive group flies a short distance, typically only a few dozen yards, before clustering temporarily on a fixed object like a tree limb or fence post. This temporary cluster, which can remain for a few hours to several days, serves as a staging area while the search for a permanent home is finalized.
Finding a New Home
During this clustering period, experienced forager bees, known as scout bees, are dispatched to search the surrounding area for a suitable cavity. Upon returning, successful scouts communicate the location and quality of their finds using the waggle dance on the surface of the cluster. Through this democratic process, the scouts advocate for their preferred sites until a strong consensus is reached, indicated by the majority of scouts dancing for a single location. Once the decision is made, the entire swarm takes flight, following the scout bees in a unified mass to their chosen new home.