Found this gem the other day. According to MDBG, 螞 has three different meanings:
- mā : dragonfly
- mǎ: ant
- mà: grasshopper
One character, three different tones, three different meanings.
I assume the way this character is usually used is as part of words: 螞蟻 vs 螞蚱 (oh look, and there's 螞蟥!). I also assume native speakers get this wrong too, so I'm not going to worry too much.