Srimad Bhagavatam Canto 05, Chapter 26, Text 17

SB 5.26.17

yas tv iha vai bhutanam isvaropakalpita-vrttinam avivikta-para-vyathanam svayam purusopakalpita-vrttir vivikta-para-vyatho vyatham acarati sa paratrandhakupe tad-abhidrohena nipatati tatra hasau tair jantubhih pasu-mrga-paksi-sarisrpair masaka-yuka-matkuna-maksikadibhir ye ke cabhidrugdhas taih sarvato ’bhidruhyamanas tamasi vihata-nidra-nirvrtir alabdhavasthanah parikramati yatha kusarire jivah.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
By the arrangement of the Supreme Lord, low-grade living beings like bugs and mosquitoes suck the blood of human beings and other animals. Such insignificant creatures are unaware that their bites are painful to the human being. However, first-class human beings — brahmanas, ksatriyas and vaisyas — are developed in consciousness, and therefore they know how painful it is to be killed. A human being endowed with knowledge certainly commits sin if he kills or torments insignificant creatures, who have no discrimination. The Supreme Lord punishes such a man by putting him into the hell known as Andhakupa, where he is attacked by all the birds and beasts, reptiles, mosquitoes, lice, worms, flies, and any other creatures he tormented during his life. They attack him from all sides, robbing him of the pleasure of sleep. Unable to rest, he constantly wanders about in the darkness. Thus in Andhakupa his suffering is just like that of a creature in the lower species.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
From this very instructive verse we learn that lower animals, created by the laws of nature to disturb the human being, are not subjected to punishment. Because the human being has developed consciousness, however, he cannot do anything against the principles of varnasrama-dharma without being condemned. Krsna states in Bhagavad-gita (4.13), catur-varnyam maya srstam guna-karma-vibhagasah: “According to the three modes of material nature and the work ascribed to them, the four divisions of human society were created by Me.” Thus all men should be divided into four classes — brahmanas, ksatriyas, vaisyas and sudras — and they should act according to their ordained regulations. They cannot deviate from their prescribed rules and regulations. One of these states that they should never trouble any animal, even those that disturb human beings. Although a tiger is not sinful if he attacks another animal and eats its flesh, if a man with developed consciousness does so, he must be punished. In other words, a human being who does not use his developed consciousness but instead acts like an animal surely undergoes punishment in many different hells.
Srimad Bhagavatam Canto 05, Chapter 26, Text 16
Srimad Bhagavatam Canto 05, Chapter 26, Text 18