The Essenes did not leave a written history or a full written record of their teachings.  This is due mostly to them not trusting the written word.  There were two main reasons why. 

1) They felt that if they put their history and teachings in writing it could fall into the wrong hands and be misused.  For that reason,what they did write down was usually codified so it could not be entirely understood without knowing the key to the code.

2) They felt that writing was often used to spread lies and give legitimacy to false teachings.  If you don't think that is true, remember that today the wealthiest and most honored writers are those who write fiction.

Because of the lack of a written history, many historians believe the Essenes only existed for two or three hundred years.  The Greek historian Philo tells us they were around for thousands of years, but few historians believe that.  Philo was correct.