Africanized bee
Africanized bees are hybrids of the African honeybee, Apis mellifera scutellata, with various European honeybees such as the Italian bee A. m. ligustica. These hybrids tend to retain the certain behavioral traits of their African ancestors, specifically a tendency to frequently swarm, to live in ground cavities, to have a high proportion of "soldier" bees, to be highly defensive and to pursue and sting percieved threats in greater numbers over longer distances. Morphologically they are similar to the european bees in size, with only a slightly shorter wing that may be determined only by examination of a large sample. They are descended from 26 Tanzanian queen bees accidentally released in 1957 in Southern Brazil from hives operated by biologist Warwick E. Kerr, who had interbred European honeybees and bees from southern Africa. Hives containing these particular queens were noted to be especially defensive. Kerr was attempting to breed a strain of bees that would be better adapted to tropical conditions (i.e., more productive) than the European bee used in North America and southern South America.
Aggressiveness
Africanized bees are characterized by their aggressiveness in establishing new hives and in their vigorous defensive behavior, attacking perceived hunters, including people. Over the decades, hundreds of deaths in the Americas have been attributed to them, many resulting from multiple bee stings. This defensiveness has earned them the nickname "killer bees", the aptness of which is debated. European honeybees also kill people due to allergic reactions, and it is difficult to estimate how many more people may have died than would have in the absence of Africanized bees.
Geographic spread
As of 2002 they had spread from Brazil south to northern Argentina and north to South and Central America, México, Texas, Arizona, New Mexico, and southern California. They are spreading north at a rate of almost two kilometers (about one mile) a day. In tropical climates they compete effectively against European bees. There have been many opportunities to control this pest by the introduction of non-defensive relatives, particularly at the Isthmus of Panama, but various national and international agricultural departments proved themselves incapable of action, and remain so to this day. Note that this same species is kept in South Africa using common beekeeping practices without problems of excessive defensiveness.
Geographic limits
Recent evidence suggests that Africanized honeybees are less able to survive a cold winter. This is seen in the southern limit of the spread of Africanized bees in eastern South America. There are now stable geographic zones in which Africanized bees dominate, a mix of Africanized and European bees are present, and in the southern reaches only non-Africanized bees are found. As the Africanized honeybee migrates further north through Mexico, colonies are interbreeding with European honeybees. This appears to be resulting in a dilution of the genetic contribution of the African stock and a gradual reduction of the aggressive behaviors. Thus Africanized bees are expected to be a hazard mostly in the Southern States of the United States. In California they have been seen on the Pacific Coast as far north as Santa Barbara and are expected to eventually occupy the San Francisco Bay Area. Within the Central Valley in 2004 Africanized bees were involved in an attack in Modesto, having previously (2003) been seen in Bakersfield. The cold weather limits of the Africanized bee have driven professional bee breeders from Southern California into the harsher wintering locals of the northern Sierra Nevada (US) and southern Cascade range. This is a more difficult area in which to prepare bees for early pollination placement, such as is required for the production of Almonds as the bees must be fed, rather than released for foraging.
Difficulty in determination
The popular term 'Africanized bee' has only limited scientific meaning today because there is no generally accepted fraction of genetic contribution used to establish a cut-off. While the native African bees are smaller, and build smaller comb cells, than the European bee, their hybrids are not smaller. They do have slightly shorter wings, which can be reliably recognized only by performing a statistic analysis on micro-measurements of a substantial sample. One problem with this test is that there is an also an Egyptian bee, also present in the southeastern United States, that has the same morphology.
Effects of selective breeding
In the European Bee (intentional selection)
The chief difference between the European races or subspecies of bees kept by American beekeepers and the Africanized stock is attributable to selective breeding. The most common race used in North America today is the Italian bee, Apis mellifera ligustica, which has been kept for several thousand years. Naturally beekeepers tended to eliminate the fierce strains as they did, and the entire race of bees has thus been gentled by selective breeding.
In the African Bee (natural selection)
In central and southern Africa, bees have had to defend themselves against other aggressive insects, as well as honey badgers, an animal that also will destroy hives if the bees are not sufficiently defensive. In addition, there was formerly no tradition of beekeeping, only bee robbing. When one wanted honey, one would seek out a bee tree and kill the colony, or at least steal its honey. The colony most likely to survive either animal or human attacks was the fiercest one. Thus the African bee has been naturally selected for ferocity.
The Assassin Bee?
The lore
In Brazil, Apis mellifera scutellata and its hybrid is known as the Assassin Bee, for its supposed habits in taking over an existing colony of European bees. According to this lore, their queen waits outside while several worker bees infiltrate the hive by bringing in food, where they will then locate and kill the queen. The new queen will then enter and take over the hive.
The danger to apiculture
It has been established that in a partially Africanized hive these aggressive bees can even "recruit" more gentle bees in attacks upon intruders. If true, this habit can make Africanized bees dangerous in areas where European bees are kept for agricultural purposes, since an existing queen may be replaced without the usual out-swarming or supercession, conditions more readily observable by the beekeeper.
Genetic evidence
Evidence for the accuracy of this report can be found in the fact that of Africanized bees in Brazil, about one third have mitochondrial DNA indicating a female ancestor of African origin. If the Africanization was attributable only (or even mostly) to the well known superior breeding efficiency of Africanized (male) drones, such "mother" DNA would much less prevalent. Although some bee species (such as the Cape Bee Apis mellifera capensis of South Africa) are known to be able to propagate additional females via egg laying female workers, this is not believed to occur in A. m. scutellatta.
Behavioral evidence
Apis mellifera scutellata is well known for sending from the hive numerous tiny swarms - a queen and only a few attendants. Such a small swarm should be incapable of starting a colony on its own, lacking enough workers for all the tasks required to support a queen. For this behavior to have survived through natural selection it may be arguably inferred that it likely has some utility to the survival and propagation of the species. The supposed assassin behavior is not inconsistent with this argument and is actually reinforced by it.
Gentle Africanized bees
Not all Africanized hives are defensive; some are quite gentle, which gives a beginning point for beekeepers to breed a gentler stock. This has been done in Brazil, where bee incidents are much less common than during the first wave of the Africanized bees' colonization. Now that the Africanized bee has been gentled, it is considered the bee of choice for beekeeping in Brazil. It is better adapted to the tropics and so is healthier and more industrious than European bees. Note that A. m. scutellata" in South Africa is the same species as the Tanzanian bee and yet is very manageable, being kept by beekeepers without extraordinary precautions.
Queen management in Africanized bee areas
In Mexico, where Africanized bees are well established, pollination beekeepers have found that a purchased and pre-bred non-Africanized queen may be used to locally create a first generation of virgin queens that are then bred in an uncontrolled fashion with the local wild Africanized drones. These first generation Africanized queens produce worker bees that are manageable, not exhibiting the intense and massive defense reactions of subseqent generations. This offers a relatively economical method of safe local beekeeping under what would otherwise lead to hazardous conditions.
How to avoid bees
Use caution with power mowers
Bees are sensitive to low frequency vibrations and so an engine driven lawn mower may elicit a defense response from a hive or swarm.
Walk with care in clover and near picnic sites
Take care not to walk barefoot on lawns containing blooming clover, which attracts foraging bees. Meat eating wasps can be attracted to food scraps near a picnic site and usually forage close to the ground.
Avoid perfume, cologne and scented cosmetics
Foraging bees will seek out floral scents. Such a bee will be harmless to you unless you swat at it, as it is only trying to find a flower. Yellowjackets can be much more aggressive, even to the point of biting.
Beware of head-butting bees
Honeybees usually have a small number of sentry bees patrolling the perimeter of the hive's territory. In some if not most cases, these sentry bees will initially head-butt (not sting) any animal that enters the hive's territory. If the animal continues closer to the hive, stinging will ensue.
If bees start head-butting you, use this behavior as a warning to retrace your steps and walk away from the hive. Choosing any other path could lead you deeper into the hive's territory.
Wear light colors
Honeybees react to dark colors. Knowing this, beekeepers always wear white (or light colored) protective suits when working with bees during daylight. Bees have poor night vision and so beekeepers wear dark colors when collecting swarms after sunset. When traveling through areas with bees, wear light colors to avoid attracting bees. Bees are inactive at night and are unlikely to be encountered unless you bump into a resting swarm.
Water meter chambers
While an occasional behaviour of European bees, African and Africanized bees are known to frequently nest in ground cavities. In suburban areas, a favored place is the in-ground concrete chamber that contains a water meter. The small lifting hole in the cover becomes the entrance to their hive. If the outside air temperature is over 60°F (15°C) you will probably see bees using this entrance if they are present, otherwise, use caution if you are in an area known to have Africanized bees.
Open air hives
While all bees may build open air hives in mild climates, this is much more prevalent with Africanized bees (as well as certain "rafter bees" native to southeast Asia). African bees are also much more migratory and can move the colony to an entirely new location in pursuit of good foraging (leaving behind their combs at the old location, which may be reoccupied by other swarms in the appropriate season).