[noondip]

> Veganism is a way of living which seeks to exclude, as far as is possible and practicable, all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose.

https://www.vegansociety.com/go-vegan/definition-veganism

The key is - "as far as is possible and practicable". It's entirely reasonable and quite easy to adhere to a plant-based diet, whereas avoiding stepping on ants is an impractical goal which detracts actual steps you could do to reduce harm.

Of course, there's no reason for veganism and your concern for ants to be mutually exclusive. Take Jain monks as an example.

> Jain monks and nuns represent the ideal of Jainism. These men and women try to separate themselves from the everyday world. They are not allowed to kill any living creature. They carry brooms to sweep all surfaces to avoid crushing insects accidentally. Monks may not own any property except a broom, simple robes, bowls for food, and walking sticks.

http://www.shaufi.com/b22/b22_9.htm