Once upon a time there was a huge garden of orchids. But, in their neighbourhood was a garden of roses. All the insects would go to roses. The poor orchids sat there, waiting for potential pollinators that will help them reproduce faster. But then one day, a mutant was born. The mutant could make chemicals that resembled pheromones produced by female bees. All his relatives used to laugh at him. Tell him that he smelled funny. They shamed him, called him beebaaboo and what not.
Ophrys speculum by Hans Hillewaert | CC BY-SA 4.0
But then, something interesting happened. There were male bees hovering over the mutant orchid. Spreading his pollens. And before his relatives could realize the offsprings of the mutant were all over the place. Those that did not smelled like the mutant in upcoming generations, could not keep up the pace in evolutionary competition. The mutants outnumbered the non mutants, just because they had sheer advantage of mimicking bee pheromones. But story doesn't end there.
How could it? I mean, do you think bees could always be fooled into humping a flower with no result. They did realize and learn, at least for short periods, that this is a click (read pheromone) bait. So even though mutants reproduced more frequently than non mutants, they could be better if they could get better at fooling bees. But how?
Well, looks like the history repeated itself. Just like there could be variations in chemicals that flower can produce, to attract pollinators; there are variations that occur just by random chance in shape and sizes of flower. It so happens, that a mutant was born whose flower looked somewhat like the female bee. Yet again it was made fun of, by its relatives. But, history repeats itself. The shape gave a little higher advantage to new mutant over the old mutant. It was better at fooling bees and reproduced a tat bit more than older version.
The new generations had its own variation in shapes. Those that were closer to rear of the female bee plus made pheromone mimics too kept getting selected over. What you see today as bee orchid is generation after generation of optimization in fooling bees to fruitlessly hump the flowers. But it is fruitful for bee orchid. Even though bees have to pay a small price for this, but a garden full of flowers is in their benefit nevertheless.
In a nutshell, this biological process is evolution of sexual mimicry. It is not something specifically guided to look like female bee. It is a random process, fueled by natural selection. In fact there are many kinds of mimicry in nature. There is one in which some butterfly mimics the features of those toxic butterflies that the predators don't find palatable (see Batesian mimicry). There are cases where two equally noxious species evolve to look like each other. Probably because they count on each other to teach predator a lesson (see Müllerian mimicry). Then there is human induced mimicry in weeds. We domesticate crops and kill the weeds. But some mutants that happen to look similar to our crops we harvest, gets advantage over those we can see easily (see Vavilovian mimicry). Then there is aggressive mimicry - in which a predator shams the prey into thinking that its either harmful or even helpful. The prey let's its guard down and predators enjoy the party. The technical term for kind of mimicry you are looking in orchids is Pseudocopulation.
I will leave some links below for further reading in this context.
I hope this helps.
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