Bugs, Why does it always have to be bugs?
To provide a serious answer to a silly (I presume, given your smilies) question....
probabley cause we can easily imagine a insectoid race as being a logical (ish) analog to a mamilian race.
but, its harder to do them on TV in terms of make up budgets
So, when it comes to an RPG we all think 'Ah! I'll be orginal and do a insectiod race cause I've never seen them on TV but I can do it cause I don't have a make up budget!' 
And I include myself in that - my latest race is insectiod 
Later days!
Mark
'Wish I could Help you....Wish I could tell you,
That I am real, I'm not something you invented,
That I'm not everything you want me to be.'
'And I am...Ageless. And I am....Invincible.'