The origin of this phrase is an aggressive attack on prey by sharks (yes I know the above picture is not of sharks *grin*) that can result on them turning even on each other. ( source ) Looting and rioting always makes me think of the phrase feeding frenzy due to the actions that are taken against each other, We are our own and yet we turn on each other for such ridiculous reasons. 

The origin of this phrase is unknown. It was first seen in print in the 18th century when political writer Edmund Burke said “having looked to government for bread, on the first scarcity they will turn and bite the hand that fed them.” ( source ) Based on that, and the definition which includes the idea that biting the hand that feeds you is a way to say disrespect is being shown to the person providing necessities, the following are some examples of the phrase.