Though calling them defensive would technically be correct, we lean more towards calling them aggressive when they defend themselves aggressively. The term "defensive" is usually not the first word that comes to mind when an animal tries to bite/sting us and we don't consider ourselves to be attacking it (even though they technically are defending their territory). I don't see the issue as being important enough to hold back every time I'm going to use the word "aggressive" for an arachnid though.
I do think the word deadly is overused in news articles and such. It's just a tacky way of making the material sound more dramatic.
I do think the word deadly is overused in news articles and such. It's just a tacky way of making the material sound more dramatic.