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Why Are Killer Bees So Slow?Aren't they supposed to be here already?

By Brendan I. Koerner
Posted Thursday, Aug. 26, 2004, at 5:32 PM ET
Their turnoffs are winter, mites, and fire ants

The dreaded Africanized honey bee—better known as the "killer bee"—may be buzzing slightly northward. Entomologists believe that an Africanized swarm was responsible for an attack in Tipton, Okla., earlier this month. Africanized bees were first discovered in Texas in 1990, setting off panicked reports that they'd be ubiquitous throughout much of the United States in a matter of years. But they've only made it to six Southwestern states so far. Why are the killer bees moving so slowly?

No one's entirely sure, but the prevailing theories include the bees' inability to cope with several facts of life in the Lower 48: wintry conditions; competition from European honey bees; the ravages of parasitic mites and predatory fire ants; and effective quarantine programs. Originally, entomologists estimated the bees' migratory speed at between 200 and 300 miles per year. They based that estimate on how quickly the bees tore through South and Central America, after African bees were first brought to Brazil in 1956. The bees were imported because European honey bees, which are common in the United States, were not well-suited to Brazil's more tropical climate; the Brazilian government wanted to create a European-African hybrid that could produce more honey. Many of the African bees escaped the following year and quickly blazed a path south to Argentina and north to Central America and Mexico.

But ever since the Africanized honey bees first hit Texas, the bees' northward march has slowed to a crawl. Cold winters may have something to do with the deceleration, as Africanized bees do not store adequate food supplies for the harsh months. Some entomologists have noted that the bees have yet to migrate beyond the 34th parallel south in Argentina and so are unlikely to go much beyond 34 degrees north in the United States. At present, a few killer bee colonies have been found in southern Nevada, which is slightly north of the 34th parallel, as is Tipton (though just barely). It's worth noting that Africanized honey bees have been spotted high up in the Andes, so it's possible that they're hardier than researchers imagine.

Another popular explanation for the bees' slowing migration is competition from European honey bees. Africanized queens are free to mate with European drones, and perhaps this has resulted in a dilution of the Africanized gene pool. (Africanized and European honey bees look virtually identical to the naked eye, and genetic tests must be used to tell them apart.) Africanized colonies may also have felt the ravages of tracheal mites, as well as fire ants that prey upon the swarms. Since their migrating swarms tend to be small in size and they tend to build nests nearer to the ground than their European cousins, Africanized honey bees make for an easy fire-ant snack.

Lastly, some credit must be given to state quarantine programs, especially in Texas. There, 152 counties have been officially listed as playing host to Africanized honey bees. Beekeepers from these counties are not permitted to transport their hives outside county lines, unless their bees have been certified by state inspectors as non-Africanized.

Africanized bee experts stress that although the insects are indeed dangerous when provoked, they're nowhere near the menace portrayed in several sensationalistic TV movies, such as 1974's Killer Bees and 1995's Deadly Invasion: The Killer Bee Nightmare.

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Brendan I. Koerner is a contributing editor at Wired and a columnist for Gizmodo. His first book, Now the Hell Will Start, is out now.
Photograph of a bee by Lynda Richardson/Corbis.
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