It's not how aggressive they are. Bees are never aggressive. Their defensive nature can be misinterpreted as aggression, when in reality, they have misidentified an unwitting intruder as a threat. Whether the bees are of European or Africanized descent, they will both keep a specific defensive perimeter sphere around their colonies. Africanized strains of honeybees evolved with animals like honey badgers attacking their colonies. Because of this, they have to be much more defensive than European honeybees, and must project a greater defensive perimeter in order to deter and repel a threat before it actually makes it close enough to the colony to attack it.
If you stand around a bee colony after being stung, you will be infused with alarm pheromone which is left by each bee as it stings. You will literally become a "marked man" That pheromone instructs any other bee in the area to sting you until you either move out of their defensive perimeter....or stop moving. The more bees that sting you, the stronger the pheromone deposit becomes on you. Alternatively, if you're just moving into their defensive sphere, bees will sometimes "bump" you. If this happens, go back the way you came to a safe distance, and re-evaluate your work area before proceeding. Bees don't like to sting if they don't have to, as it can cause a massive loss of colony workers once that first sting occurs. They will often times try more peaceful means to let you know that you're in their territory and that they'd like for you to leave, without stinging.
Africanized honeybees in the US, tend to be an over-exaggerated phenomenon. Any disturbed colony will become hot and agitated and will begin a stinging defense that quickly escalates. Once a colony launches its defense, there are going to be thousands of bees involved and they will all have one interest, to drive away the intruder. The difference between Africanized and European honeybees lies in the distance they will pursue a perceived threat to drive it away from their colony. A European colony won't have to launch as serious a defense against say, a raccoon, as an Africanized colony would against the aforementioned honey badger
It can help to understand the motivation of bees as regards their defensive stinging. They will only sting in order to protect their home/goods/children against home invaders, as you would likely do if you felt your home was being invaded with malicious intent. Other than that, an individual bee out foraging is unlikely to feel motivated to sting when away from the colony, unless stepped upon, or caught and harassed.
It can be helpful to understand what bees require in the way of habitat. They need a sheltered enclosure with sufficient volume to allow for nursery comb and additional comb for pollen and honey storage. If you think of the size of a couple bee boxes stacked on top of each other, that's the minimum volume required for a viable colony to establish. Bees will also prefer a void which is accessed by a smaller hole as the smaller the entrance, the more easily it can be defended by guard bees in the colony. Because of this volume requirement, feral bee colonies will tend to be located in voids in trunks or larger stems, although sometimes a colony will outgrow that space and expand so that it hangs pendulous from limbs in the canopy. As those colonies are more exposed, they will be less tolerant of the approach of a potential intruder.
A pair of field glasses can help a great deal in identifying bees and other sources of elevated risk in a tree canopy. I heard the late and very great Bruce Smith refer to a pair of field glasses as "a poor man's bucket truck". Another tip he gave, was to hold the power head of a running chainsaw against the trunk of a tree and rev it a few times during the initial pre-climb inspection, before anything is set up. If there are bees in that tree, those transmitted vibrations will induce them to come out to see what's going on, and you will have an opportunity to vacate the area unscathed.
Most of the animals which attack bee colonies and feed upon larvae have dark colored pelts like bears, so it can be helpful to wear lighter colored clothes when working in trees during active bee season. This is why beekeepers jackets and suits are made of white material.
Stay safe everyone!
