How dangerous are killer bees? What to do if you encounter them?

31.07.2017. 19:00

The Africanized bee, also known as Africanized honey bee, is colloquially known as the killer bee. This bee is a hybrid produced by cross-breeding African honey bee with Western honey bee species, especially Italian bee. Their name itself can send chills down your spine; it sounds like a title of some horror movie. They earned the "killer bee" title because of high defensiveness and easy provocation. From time to time, victims of killer bees make a headline on the news. What makes killer bees dangerous is that they attack in big swarms. The attack of a killer bee swarm can result in up to 10 times more stings than from European honey bee. Their venom is not stronger than the venom of a European honey bee, but a high number of stings increases the venom dosage and its effect. Even though they can be very dangerous, their attacks are rare. Learning more about their behavior and the reason behind it can help you stay safe. Firstly we should learn about their history and how they were created.

A little bit of history

There are many subspecies of Apis mellifera, in many geographic locations and they are cross-fertile. The origin of Africanized honey bees in the Western Hemisphere is from hives operated by biologist Warwick E. Kerr. He interbred European honey bees and honey bees from southern Africa to produce a breed of bees that would be better adapted to tropical conditions and produce more honey than European honey bees.  

The apiary with these Africanized bees was located in Rio Claro, São Paulo, in the southeast of Brazil. Right from the start, Kerr noticed that these bees were more aggressive than regular bees. The hives had queen excluders which prevented larger queen bees and drones from getting out and mating with local bees.

In October 1957 a visiting beekeeper noticed that queen excluders interfered with the movement of worker bees, so he removed it. Unfortunately, that resulted in an escape of 26 swarms of these Africanized bees. The escaped bees cross-bred with local European colonies which helped in spreading of Africanized bees throughout Americas. Their spread was unassisted by humans and rapid, earning them the reputation of being the most successful biologically invasive species of all time.

The first colony of Africanized bees in the U.S. was discovered in 1985 at an oil field in the San Joaquin Valley of California. One theory is that the colony came from South America by being hidden in a load of oil-drilling pipe shipped from there. In 1994, in Tucson region of Arizona, a study found out that only 15% of swarms have been Africanized. But, a study from 1997 discovered that number had grown to 90 percent!  

In tropical climates, Africanized bees out-compete European bees very efficiently which affects the regular colonies. These bees were rapidly spreading to the north, so scientists were trying to come up with solutions to slow them down. There were discussions about the strategical placement of large numbers of docile European-strain hives. Unfortunately, national and international agricultural departments weren't able to prevent their spread. As scientists gained more knowledge about the genetics of these bees, they realized that such attempt would not be successful.

Africanized honey bees have quickly spread throughout South and Central America, and since 2012 they have spread to southern parts of USA: California, Texas, Arizona, New Mexico, Oklahoma, Florida, Alabama, Louisiana, and Arkansas. Their spread through North America is slower because of weather limitations. Africanized honey bees cannot withstand colder climates like European honey bees.

How to recognize Africanized bees?

Africanized bees or killer bees are very similar to European honey bees so they cannot be distinguished easily. We must warn you that if you suspect that a wild colony might be Africanized, the identification should be left to the professionals. Disturbing Africanized honey bees can be very dangerous if you don’t know what you are doing!

Several differences between a killer bee and European honey bee include:

  • Physical characteristics

  • Aggression

  • Time to calm down after defensive behavior

  • Foraging in groups or alone

  • DNA

  • Nest usurpation

  • Choice of nest locations

  • Level of reproduction and nest abandonment

Physical characteristics

Killer bees are about 10% smaller than European bees, but that difference cannot be noticed with a naked eye. Some other physical characteristics can be checked only using laboratory equipment. Laboratories use morphometric analyses to determine if a colony is Africanized or fully African.

The physical characteristics of honey bees important for identification are:

  • the size of body parts

  • coloration of body parts

  • measurement of wing venation patterns

These measurements are collectively called morphometry. Morphometry has been used as a bee identification tool since the 1960s, and it is the first step in the identification of bee races.


The higher defensiveness of killer bees than European honey bees is a well-known characteristic. Some experts believe that increased aggressiveness may be partially induced by man. In Europe, beekeeping is more common, and native bees are bred for gentleness and ease of management. Beekeeping is essentially management of honey bee colonies by humans, promoting taking care of the hives. In Africa, a common practice is 'honey hunting' which includes complete destruction of the hive to harvest its contents. Honey hunting might have resulted in bees getting more defensive of its nest. Other possible reasons for higher defensiveness may be resource availability, climatic stress, and predation by mammals, reptiles, and birds.

A common characteristic of all bees is that they will defend their nest from intruders who get too close. If colony feels threatened, European honey bee colony will usually send 10 - 20 bees, while killer bee colony may send hundreds of bees. A killer bee colony also defends a larger radius around their nest and require less stimuli to start the attack.

These characteristics make killer bee very dangerous and able to kill large mammals, including humans. As we already mentioned, their venom is not any stronger than regular bee venom. What makes them dangerous is the number of bees that attack the victim.

Time to calm down after agitation

European honey bee colony usually calms down after about 20 minutes, while killer bees can stay aggressive for several hours.

Foraging in groups or alone

Africanized bees are more solitary than European honey bee, so they forage alone. Another foraging behavior is that they forage at a different time than regular bees, foraging earlier in the morning or later in the evening. While regular bees are more sensitive to temperatures and rain, Africanized bees go out even during cold weather and light rain.


DNA testing is the only way to be certain whether an individual bee is Africanized. DNA testing is used to confirm African bloodline in the specimen.

Nest usurpation

Colony takeover starts with Africanized swarms containing a queen landing on walls of European bee hive. With time their worker bees exchange pheromones and food with European bee workers which ensure killer bee integration. In the final step European honey bee queen is exchanged by Africanized queen. The fate of the European honey bee queen is still uncertain; she is maybe killed by the invading queen. European honey bee doesn't show this behavior and often falls victim to it.

Choice of nest locations

Africanized bees are less picky about the nest location and nest in smaller spaces than European honey bees. The hive of Africanized bee is usually about 3.8 - 19 l in size, while the hive of European honey bee is a lot bigger (around 10 l). This also makes it more difficult to see nests of Africanized bees before it's too late. Some of the places their nests have been found in are cement blocks, water meter boxes, house eaves, old tires, cavities in the ground, barbecue grills, and hanging from tree branches. European honey bee usually won't be found in such locations because they look for larger spaces like chimneys, and tree hollows. Smaller nesting sites of Africanized bees is one of the main reasons why they are frequently encountered by humans.

Level of reproduction and nest abandonment

Africanized honey bees swarm and abandon their nests more often than European honey bees. European honey bees usually swarm one to three times per year, while killer bees swarm more than ten times per year. Frequent swarming can reduce the population left behind in the hive so a new queen might have to be regularly introduced. If the Africanized honey bee colony is repeatedly disturbed, they are very likely to abandon their nest.

Africanized honey bees have smaller swarms than European honey bee, but they reproduce in greater numbers. Because of it killer bees easily outnumber other species.

How to recognize Africanized bees

What makes them so successful?

An important factor in their successful overtake of European honey bee colonies is mating biology and developmental time.

Mature virgin queens of all western honey bees leave the colony to mate with drones. The mating is done in the air, and only the fastest drones get the chance to mate. Africanized colonies produce more drones than western honey bees, so they are more likely to mate with European honey bee queen. In the next 7-10 days, the queen mates 10-20 times and stores semen in an organ called spermatheca.

The newly mated queen bee lays fertilized and unfertilized eggs in designated wax cells. Fertilized eggs develop into queens and workers, while unfertilized eggs develop into drones. Since drones emerge from unfertilized eggs, they inherit genetic material only from their mother. If the queen if Africanized the drones will also be Africanized, further helping the spread of Africanized bees.

All bees undergo metamorphosis during development from egg to adult, but the time of development varies depending on the subspecies. Africanized honey bees usually develop faster than European honey bees. The queen that emerges first kills all her queen sisters that have not yet emerged. Because of that Africanized queen is more likely to become a new matriarch to the colony.

Further mating of Africanized virgin queens is done in an area with a higher density of African drones. Since African genetic traits are mostly dominant, the European gentler behavior gets replaced almost entirely.

How dangerous are killer bees to humans?

Heightened defensive behavior of Africanized honey bees makes them dangerous to humans. The elders, disabled individuals, and children are at the highest risk of deadly attacks by killer bees. They cannot escape or have a hampered ability to escape an attack. So far Africanized bees have killed around 1000 people.

Nesting habits of killer bees often put them near humans. They can be agitated by vibrations and loud noise from machinery like lawnmowers. Because of this, precautions should be taken in areas with killer bees. They include staying away from the swarm or hive, removing wild colonies from places where humans often frequent, and being alert of bees flying. If bees are often flying in or out of an area, that might indicate the presence of a hive. The precautions are not suggested to spread the fear of honey bees, but only to encourage respect for honey bees and caution.

A lot of attacks in the USA occur when people know the nest is present but don't have it removed, or even try to remove it themselves.

Killer bee attacks can be prevented by limiting the number of nesting sites available to the bees. You should remove any unnecessary debris from an area, close any holes in the walls, plumbing and electrical related gaps wider than 30 mm. Chimneys and similar spaces that cannot be closed off completely should have protective bee-resistant mesh.

Additionally, walls and eaves of structures should regularly be checked for bee activity.

What to do if you encounter killer bees?

Even if you live in an area with Africanized honey bees, the chances of you being stung are small. Killer bees aren't just on the lookout for victims to sting; they are just defending their nest. But since they defend their nests very aggressively, you should know what to do if you encounter them.

1. Be aware of the triggers that might provoke killer bees

Prevention is the best defense, so if you encounter a beehive do not get too close or disturb it, bees might think that the hive is under threat. Lead by their protective instinct they will defend the hive by stinging you. Sometimes you might not notice the hive while hiking or walking outside; then it is important to make same precautions to lower the chances of being attacked.

  • Do not make loud noises and don't shout close to the hive. Avoid using any machinery because their noise can also disturb the bees. Some of such tools are lawnmowers and chainsaws. For the safety of your pets, especially dogs, keep them away from the hive. Dog's barking can encourage the attack

  • Don't disturb or poke the hive. If you need/want to remove the hive, call the professionals who will remove the hive safely.

  • If you are in an area known for having Africanized bees, don't wear shiny jewelry, strong perfume, dark or colorful clothing.

2. If killer bees start attacking you, you should RUN!

In a case of an attack run away as far as possible. Do not stop to help others unless they are children or disabled. You cannot stop the attacking bees so trying to help others will just result in you being injured as well. Anyone in the vicinity of an attack should be warned and told to run to shelter. Run in a straight line and don’t flail your arms or swat at the bees because it could agitate the bees even more. Crushed bees leave pheromones that will attract even more bees. Since killer bees are slow flyers, healthy people are mostly capable of outrunning them.

If you notice someone being attacked by bees, encourage them to run away and seek shelter. Do not try to rescue them yourself, call the emergency services.

3. Run into the wind

Running into the wind will slow down the bees and enable you to run away. Running through bushes and high weeds might also slow them down.

4. Don’t forget to protect your face, especially your eyes

While you are running, you should protect your face. If you don't have anything else, you can pull your shirt over your face or your arms. You should protect your sensitive had areas, like eyes, as much as you can. Whatever you choose do not let it slow down your running. If you are carrying an infant, then keep their face tucked into your body so bees cannot get to their face.  

5. Avoid getting into water

Getting into water won’t help you, killer bees will wait for you to come up for air and continue the attack. If you are already under attack, you have been marked by bee alarm pheromones which cannot be washed of easily. Staying in one place will just attract even more bees so seeking shelter should be your priority.

6. Seek shelter

Keep running until you reach shelter. Some killer bees might follow you inside, but you should be able to shut most bees outside. Any bees that followed you inside will be disoriented by the lights inside and will fly to the windows.

If you cannot find any shelter, then use sleeping bags, blankets, tent, or anything that could cover you.

7. Take care of stings, and seek medical attention if necessary

After you have found shelter or outrun the killer bees, you should take care of stings.

Remove all stingers. Even though a bee dies after stinging you, the stinger left in your skin still injects venom for a short period of time. Stingers should be scraped off with your fingernail, the edge of a credit card, a dull knife, or something similar. DO NOT PULL OUT STINGERS WITH TWEEZERS OR YOUR FINGERS! Putting pressure on the stinger will inject more venom! If you didn’t receive a lot of stings and you are not allergic to bee venom, you can treat the stings yourself.

If you notice more than 15 stings or any signs of allergic reaction, seek medical attention immediately. The average number of stings a healthy person can tolerate is 7-10 stings per pound of body weight. An average adult could withstand around 1100 stings, but 500 stings can be deadly for a child. People allergic to bee venom are at significant risk of anaphylactic shock even from one sting.

An agitated killer bee swarm is dangerous to anyone in the vicinity, so it is important to contain it. Do not attempt it yourself, call the police and notify them about the attack. They can send professional beekeepers who will contain the swarm safely.

How beekeepers manage Africanized bee hives?

Africanized honey bees can be dangerous but don't forget they also pollinate crops and produce honey. Managing Africanized bees can be done safely and efficiently, but they require a different set of skills than European honey bees.

In the U.S. beekeepers are discouraged from using Africanized bees, while in Central and South America they are widely accepted. The reason behind it might be the public perception of honey bees or U.S. legal system. Because of the presence of Africanized bees, some South American countries are among leading producers of honey.

Firstly, Africanized bees require different management of the hives. Beekeepers working with them keep only one bee colony on the individual hive stand. This is done to avoid agitating several colonies while working with only one colony.

While working with a killer bee hive, beekeepers use a lot of smoke to calm down the bees. Some believe that smoke masks bee warning pheromones which lessens their defensiveness. The colony should be smoked well before any work is done. If the colony is already agitated, using smoke might not calm the bees.

Managing killer bee hive puts a beekeeper up close to easily agitated bees, making a full bee suit mandatory. Bee veils protecting the head are worn by almost all beekeepers. A bee veil has a mesh protecting the face, usually colored black to reduce the sun's glare. Africanized bees attack dark colors, so dark mesh gets covered in bees. Beekeepers who want to keep the bees off their veils, use white veils. As additional protection, beekeepers managing killer bees often tape their bee suits to their botos and gloves. That way they are limiting the possibility of bees entering the suit.

Killer bees can be easily provoked, and then they are very aggressive

Many people get scared even from a mention of a killer bee. Killer bees can be easily provoked, and then they are very aggressive. Their swarms are capable of killing even larger mammals, including humans and horses. Unfortunately, without laboratory analysis you cannot differentiate Africanized bees from other bee species. Because of it, your best protection is to treat all bees as Africanized. Meaning that you should not approach their hive, or try to remove it yourself. If you notice a beehive or a lot of bees close to your house, try to contact a local beekeeper association instead of pest control. That way a professional beekeeper can remove the nest safely without killing the bees. You should not forget that bees are important pollinators, even killer bees, so you should avoid killing them.