Bees are flying insects of the Hymenoptera, which also includes ants, wasps and sawflies. There are about 20,000 species of bees. Bees collect pollen from flowers. Bees can be found on all continents except Antarctica.

Bees fall into four groups:
Honeybees, including the Africanized honeybee.
Bumblebees: 250 species in the Apidae family.
Stingless bees: 550 species in the Meliponini.
Solitary bees: solitary in the sense that every female is fertile, and usually lives in a nest she builds herself. There are quite a few of these, for example the carpenter bees, leafcutter bees and mason bees (and there are others).

The European honey bee (called Apis mellifera by biologists), is kept by humans for honey. Keeping bees to make honey is called beekeeping, or apiculture.

Evolution 
Flowers were pollinated by insects such as beetles long before bees first appeared. Bees are different because they are specialized as pollination agents. Their body and behavior  make pollination easier. Bees are generally better at the task than other pollinating insects such as beetles, flies, butterflies and pollen wasps. The appearance of such floral specialists is believed to have driven the adaptive radiation of the angiosperms, and, in turn, the bees themselves.

Bees, like ants, evolved from wasps. The ancestors of bees were wasps in a family which preyed on other insects. The switch from insect prey to pollen may have come from the capture of prey insects that were covered with pollen when they were fed to the wasp larvae. Similar behaviour could be switched to pollen collection. This same evolutionary scenario has occurred within the vespoid wasps, where the group known as "pollen wasps" also evolved from predatory ancestors. 

A recently reported bee fossil, of the genus Melittosphex, is considered "an extinct lineage of pollen-collecting Apoidea, sister-group to the modern bees", and dates from the Lower Cretaceous (~100 mya). Features of its morphology  place it clearly within the bees. It still has two ancestral traits of the legs which betray its origin. The issue is still under debate, and the phylogenetic relationships among bee families are poorly understood.

Bee bodies 

Like other insects, the body of a bee can be divided into three parts: the head, thorax (the middle part), and abdomen (the back part). Also like other insects, bees have three pairs of legs and two pairs of wings. Many bees are hairy and have yellow and black or orange and black warning colors.

Many bees have stings (like a hollow needle) on the rear of their bodies. If they get confused, angry, or scared they may sting, and inject venom, which hurts. Once a worker bee has stung it dies after a short while, but other types of bee and wasp can sting again. Some people are allergic to bee stings and may even die from them.

Social bees 
Some bees are eusocial insects; this means they live in organized groups called colonies. Honey bees, the kind of bee used in beekeeping, are eusocial. The home of a bee colony is called a hive. One hive has only one queen. 

There are three kinds of bees in a honey bee colony. A queen bee is the most important bee in the colony because she will lay the eggs. The queen bee only uses her stinger to sting other queen bees. The queen is usually the mother of the worker bees. She ate a special jelly called royal jelly from when she was young. Worker bees are females too, and they are the bees that collect pollen from flowers and will fight to protect the colony. Workers do a waggle dance to tell the others where they have found nectar; Karl von Frisch discovered this.

Drone bees (males) mate with the queen bee so that she can lay eggs.  The only function of the male drone is to mate.  They do no other work in the hive.

Haplodiploidy 
In haplodiploid species, females develop from fertilized eggs and males from unfertilized eggs. 

Because a male has only one copy of each gene, his daughters (which are diploid, with two copies of each gene) share 100% of his genes and 50% of their mother's. Therefore, they share 75% of their genes with each other.

It is unclear whether this system is necessary for eusociality.
Monogamy (queens mating singly) is the ancestral state for all eusocial species so far known, so it is likely that haplodiploidy contributed to the evolution of eusociality in bees.

Related pages
Bumblebee
Honey
Africanized honeybee
Hymenoptera

References

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