If it looks like a duck, quacks like a duck, and walks like a duck, it's probably a duck.

If it looks like a bee, buzzes like a bee, and visits flowers like a bee, it might not be a bee.

It could be a fly, or more specifically, a syrphid or flower fly.

Syrphids, also known as hover flies (from the family Syrphidae and order Diptera), are everywhere.

They hover over flowers like a helicopter over a meadow and then touch down. You'll see them nectaring blossoms, zipping from one flower to the other. When they're shadowed or startled, off they go. 

Several of them were nectaring on our newly opened pink cactus blossoms this morning.

To the untrained eye, syrphids are often mistaken for honey bees. However, think number of wings (honey bees have four wings, syrphids have two), overall size, distinct coloration, and different antennae.  Different antennae? Yes. Honey bees have long antennae bent at a right angle. Syrphids have a specialized bristle (arista) on the end of each antenna. It looks like a knob.

So, if  it looks like a duck, walks like a duck and quacks like a duck, it's probably a duck. 

If it visits flowers, it might not be a bee. It could "bee" a fly.