Aroused when wife starts her period?

For some strange reason I seemed to get heavily turned on by my wife right at the beginning of her period. She doesn't need to be doing anything or be dressed up in particular. I don't know what it is, but my libido goes into overdrive only to be shut down by my wife that she tells me its that time of the month. I cannot explain it, I do not keep account the days when she is menstruating and it seems I get attracted and aroused massively to my wife during this period of time without even knowing it. This has been happening for almost our entire married life. Is there an explanation for this?