Bread-Bakers v107.n018.4

Hi. I am new to the list and not as experienced as all of you 
guys.  I am just starting to branch out from whole wheat bread and 
white bread.  I tried to make a sour dough starter it was doing fine 
until the third day when it got fruit flies in it, yuck!  I threw it 
away.  What did I do wrong?  And how do I avoid this from happening again?

Donna