What qualifies as a "sentient being"?

[Luke]

A sentient being is an organism that experiences, that's what sentience means:)

Dogs are sentient, people are sentient, algae isn't and I am not sure about spiders:)

Spiders and all insects are sentient beings. Therefore, any Buddhist should not kill them, and this is not a joke.

I agree that algae are not sentient because they are basically like plants but are even simpler in structure. It's harder to tell if protazoa like amoebas are sentient or not.

I suppose the general rule should be "When in doubt, don't harm it." Of course, we probably kill many microorganisms each day just by walking around, so some things we can't avoid.

The Jains are experts at non-violence. I should read more about their techniques to avoid harming creatures.

[Ogyen]

perhaps one should look at sapience vs. sentience...?

Sapient beings even flies have the capability of hope and fear. If there is hope and fear, there is craving and rebirth. Sentient normally characterizes that which has senses. But since plants have a sense of pain and pleasure and differentiate the two from what research shows, perhaps we are speaking more of sapience. A sufficient sentience that produces senses and a sapience of such senses sufficient to create suffering of not getting what it needs and fear of death. The sapience of an ant hive-mind or bees. Even the smallest fruit fly has hope and fear of food/procreation for its survival. And the fact that small insects will sacrifice their lives for the sake of their offspring indicates a small sapience. Bees do elaborate dances to communicate to their mates at the hive where the pollen is, and through this they communicate in a language to each other. This is a form of primitive sapience. Spiders are certainly primitively sapient. T

he ability to hope and fear only comes from a being that has senses sufficient to experience suffering and death (which is what gives the ability to hope and fear). Bacteria have no sapience. There may be a subtle sentience, but I doubt it is sufficient to meet criteria of hope/fear. The simplest way I think of it is: can it hope or fear? If yes, then it is sentient. If no, it is not subject to karma. That way any animal or strange being that has this capability falls under one's umbrella of mindfulness and compassion towards sentient beings.

:headbow:
Ogyen.

[Aemilius]

A sentient being is an organism that experiences, that's what sentience means:)

Dogs are sentient, people are sentient, algae isn't and I am not sure about spiders:)

This is difficult to know, without first hand experience. Spiders have a nervous system, as do insects in general. Humans feel pain and pleasure through the stimuli that is transmitted through the nerves, hence it is easy to imagine that the spiders would experience in like manner.
The so called "lower life forms" react to external stimuli, you can't be sure if they also experience something? You can't rule it out, I would think.
When humans react to external stimuli, we conclude that they experience feelings, do we not ?

It is worth noting that spiders, grasshoppers etc... have tiny brains, something that is like a spinal column, a heart, tiny muscles that move their legs, and so on... You will find descriptions of it in the web, in categories like "Spider anatomy, Grasshopper anatomy".