Insects and pest control is a difficult issue for many Buddhists to consider. The First Precept does not allow the killing of living beings. This generally refers to all sentient beings which includes all animals and humans. Insects are members of the Animal Kingdom.
Many Buddhists argue that the killing of insects is just as bad as the killing of a larger animal. And when looking at passages from the Metta Sutta and other discourses about the importance of not killing living beings, it appears they are correct. Killing living beings appears to be wrong in all cases, regardless of the motivations.
However, there does appear to be some differences in the weight of the negative kamma assigned to the killing of smaller beings as compared to larger beings and humans. The Vinaya makes one such distinction, considering murder an offense so serious as to require permanent expulsion from the Sangha (Parajika 3), while killing an animal is a far less serious offence (Pacittiya 62), on a par with insulting someone, idle chatter and having a non-regulation size sitting mat. This distinction is probably based on the idea that the intentions behind killing a fellow human would be markedly stronger and more intense than those behind killing an animal.
Each of us has probably noticed that we think differently about the death of a person, the death of a warm blooded animal and that of an insect. Likewise we probably notice a difference in how we felt if we were to kill a chicken and an ant. These feeling must be partly socially conditioned but whatever their cause they do affect our minds differently and therefore have different vipaka (kamma result). This may not be a fact but could be a possible explanation for the Vinaya’s (and most peoples') distinction between killing a human and an animal.
The Buddha may have allowed the monks and nuns to eat meat according the 3 fold rule, but did not allow them to eat certain meats such as the flesh of humans, elephants, horse, dog, snake, lion, tiger, leopard, bear, and hyena (Mahavagga VI.23.10-15) even if it was generously offered. This again shows a sort of hierarchy with humans at the top, followed by these royal animals (such as elephants and lions), then lower animals, and finally insects.
Based on the above points and teachings from the Buddha, there could arguably be a hierarchy such as the following:
Humans (a parajika offense requiring expulsion from the Order for killing a human)
Large, Royal animals, such as elephants, lions, tigers (not allowed to be eaten even if offered)
Smaller animals (their flesh may be eaten, if offered to monks, nuns)
Insects (building construction and farming allowed even though they may be killed indirectly)
There will be negative kamma associated with the killing of any animal, which includes insects, but it appears that the weight of the kamma will be lesser for insects. Further evidence to this size issue is the fact that in the Vinaya texts the precept against intentional killing is broken only if the being killed is large enough to be visible to the human eye.
Although the mind is a subtle and complex phenomena and its workings are difficult to plumb, the doctrine of kamma is all too often presented in the most naive and simplistic terms. For example, one often hears people say "If you kill you will... " (fill in the gap – be killed in your next life, be reborn as a worm, go to hell, etc.).Interestingly, although not surprisingly, the Buddha criticized such generalizations:
"If anyone were to say that just as a person does a deed, so is his experience is determined by it, and if this were true, then living the holy life would not be possible, there would be no opportunity for the overcoming of suffering. But if anyone were to say that a person does a deed that is to be experienced, so does he experience it, then living the holy life would be possible, there would be an opportunity for the ending of suffering. For instance, a small evil deed done by one person may be experienced here in this life or perhaps not at all. Now, what sort of person commits a small evil that takes him to hell? Take a person who is careless in the development of body, speech and mind. He has not developed wisdom, he is insignificant, he has not developed himself, his life is restricted, and he is miserable. Even a small evil deed may bring such a person to hell. Now, take the person who is careful in development of body, speech and mind, He has developed wisdom, he is not insignificant, he has developed himself, his life is unrestricted and he is immeasurable. For such a person, a small evil deed may be experienced here or perhaps not at all. Suppose someone throws a grain of salt into a little cup of water. That water would be undrinkable. And why? Because the amount of water is small. Now, suppose throws a grain salt in River Ganges. That water would not be undrinkable. And why? Because the amount of water is great" (Anguttara Nikaya I.249).
It appears that although negative kamma, the killing of insects would be like a salt cube in the River Ganges and not seriously lead to any significant negative results, especially if done in defense of your home and family. For example a person who kills termites, wasps, or poisonous insects that entered his home after attempts to remove them failed.
