As mentioned in this answer, it is a sin to kill small creatures. It is a rational way to walk carefully in-order to avoid violence. Else, we are guilt for doing sin. We have to vigilant enough during our activities for the well-being of such creatures.
Purport of Prabhupada for a Srimad Bhagavatam verse contains an excellent reference to this discussion. Jada Bharata, a jivan muktha, used to walk cautiously to save the lives of ants.
The palanquin, however, was very erratically carried by Jaḍa Bharata due to his sense of nonviolence. As he stepped forward, he checked
before him every three feet to see whether he was about to step on
ants. Consequently he could not keep pace with the other carriers. Due
to this, the palanquin was shaking, and King Rahūgaṇa immediately
asked the carriers, “Why are you carrying this palanquin unevenly?
Better carry it properly.”
[Verse 2, Chapter 10, Canto 5, Srimad Bhagavatam]
Although Jaḍa Bharata was forced to carry the palanquin, he did not
give up his sympathetic feelings toward the poor ants passing on the
road. A devotee of the Lord does not forget his devotional service and
other favorable activities, even when he is in a most distressful
condition. Jaḍa Bharata was a qualified brāhmaṇa, highly elevated in
spiritual knowledge, yet he was forced to carry the palanquin. He did
not mind this, but while walking on the road, he could not forget his
duty to avoid killing even an ant. A Vaiṣṇava is never envious or
unnecessarily violent. There were many ants on the path, but Jaḍa
Bharata took care by looking ahead three feet. When the ants were no
longer in his way, he would place his foot on the ground. A Vaiṣṇava
is always very kind at heart to all living entities. In His
sāṅkhya-yoga, Lord Kapiladeva explains: suhṛdaḥ sarva-dehinām. Living
entities assume different bodily forms. Those who are not Vaiṣṇavas
consider only human society worthy of their sympathy, but Kṛṣṇa claims
to be the supreme father of all life forms. Consequently the Vaiṣṇava
takes care not to annihilate untimely or unnecessarily any life form.
All living entities have to fulfill a certain duration for being
encaged in a particular type of material body. They have to finish the
duration allotted a particular body before being promoted or evolved
to another body. Killing an animal or any other living being simply
places an impediment in the way of his completing his term of
imprisonment in a certain body. One should therefore not kill bodies
for one’s sense gratification, for this will implicate one in sinful
The purport clearly explains the necessity of vigilance while doing our activities.