We report on a detailed analysis of the optical light curve of the symbiotic system BX Mon , the data of which were gathered from the literature .
The light curve covers the period December 1889 March 2009 , with a gap of no observations between March 1940 and February 1972 .
The light curve is characterized by strong oscillations of peak to peak amplitude of 2 to more than 3 magnitudes .
Before the gap the fluctuations were modulated mainly by a period P _ { a } =1373 \pm 4 d. After the gap the dominant periodicity is P _ { b } =1256 \pm 16 .
Higher harmonics as well as a few beats of the two major periodicities can also be identified in the light curve .
We identify one of the beat periods , P _ { r } =656 d , as the sidereal rotation period of the giant component of the system .
The period switching that took place during the gap in the observations was possibly associated with a certain cataclysmic event , hints of which may be recognized in the LC in the first 11 years after the gap .

We suggest that the origin of the major oscillations is in periodic episodes of mass accretion from the M giant onto the hot component of the system .
After the gap they are correlated with the periastron passage of the system , and therefore appear with the binary period .
Before the gap the oscillations appeared with the diurnal cycle of an observer on the surface of the rotating M giant , whose sun is the hot component .
The event of the period switching is possibly related to an intensive magnetic activity in the outer layers of the giant star .