Africanized bees, often called “killer bees,” are known for their aggressive reputation and rapid spread across the Americas. Their presence has raised questions about their origins and how they came to inhabit new territories. Understanding their journey reveals the impact of human actions on biological processes.
The Brazilian Origin
The story of Africanized bees began in Brazil with a scientific experiment led by geneticist Warwick Kerr. In 1956, Kerr imported African honey bees from Tanzania and South Africa to a research apiary near Rio Claro, Brazil. The goal was to crossbreed these African bees with existing European honey bee populations to create a hybrid better suited for Brazil’s tropical climate. European bees, adapted to temperate zones, were not thriving in South America’s warmer, more humid conditions, leading to low honey production. Kerr aimed to combine the African bees’ resilience and prolific honey-producing traits with the more docile nature of European bees.
The Unintended Release
Despite careful planning, an unforeseen incident led to the escape of these experimental bees. In October 1957, a visiting beekeeper at the research facility inadvertently removed queen excluders from the hives. These excluders were designed to prevent queen bees and drones from leaving the hives and mating with local European bee populations. The removal of these barriers resulted in the accidental release of 26 African bee swarms into the nearby eucalyptus forest. This release marked when Africanized bees, a hybrid inheriting defensive traits from their African lineage, began their uncontrolled spread.
The Northward Migration
Following their escape, Africanized bees began a rapid northward migration throughout South and Central America. These bees possess biological and behavioral traits that allowed them to outcompete European honey bees and rapidly expand their territory. They swarm more frequently, often up to 16 times a year compared to European bees which swarm perhaps once a year, and can establish new colonies in diverse locations. Their aggressive defensive behavior, involving a larger number of bees stinging over greater distances, also contributed to their dominance. This enabled them to spread at an estimated rate of 200 to 300 miles per year, moving through the Amazon basin in the 1970s and reaching Central America by 1982.
Arrival in the United States
The northward advance of Africanized bees led to their arrival in the United States. The first confirmed natural colony was discovered on October 15, 1990, near Hidalgo, Texas, in the Rio Grande River Valley. Their arrival generated public and scientific attention, partly due to their “killer bee” moniker popularized by media. Following Texas, Africanized bees were detected in Arizona and New Mexico in 1993, and California by 1994. While their spread has slowed in temperate regions, they have established populations across much of the Southwestern U.S., becoming a permanent part of the local ecosystem.