In our routine life we kill so many insects and animals unconsciously, do we have to suffer reaction of that?

Although, we may take so many precautions to protect ourselves against the vices and sinful reactions, unconsciously we kill many ants and others insects while discharging even the most ordinary duties, such as walking from one place to another. Even while simply drinking water we kill many tiny aquatic creatures, and we also kill many living entities merely by cleansing our homes or when eating or sleeping. In sum, we cannot avoid all the sins we incur, even unconsciously, in the ordinary course of life. According to the laws of man, a person may be hanged when he commits homicide but he is not hanged when he kills lower animals. According to the laws of God; however, one also commits sin by killing a lower animal. We are punished by the laws of God for either action. Those who do not believe in the laws of God, or even in His existence, may go on committing such sins, and they are put into for committing such sins, but that does not affect the existence of God or His eternal laws.

By doing everything for the satisfaction of Vishnu (Krishna) and taking the remnants of the offerings made to Vishnu, we can get rid of the vices and sinful reactions that accumulate in the course of performing our prescribed duties.

Source: A.C. Bhaktivedanta Swami Prabhupada (2012 edition), “Message of Godhead”, Page 33