This was mentioned by Tiger on 03 Aug 99:

NEVER SWAT A FLY
Words by Buddy G. DeSylva and Lew Brown, music by Ray Henderson, ©1930.

As sung and danced by Marjorie White and Frank Albertson in the film "Just Imagine" (1930). You can see the clip on YouTube. (However, the recordings listed below are better musically, but less complete lyrically.)

[Verse 1] Love has made me tender; I now appreciate
Ev'ry little creature on this earth that has a mate.
Once I hated crickets; I couldn't stand a bee.
Now here is the motto that I follow faithfully:

[Chorus 1] Never swat a fly.
He may love another fly.
He may sit with her and sigh
The way I do with you.
Never harm a flea.
He may have a fav'rite she
That he bounces on his knee
The way I do with you.
Never stop a bee if he is going anywhere.
You may be concluding some terrific love affair.
Be careful!
Don't step on an ant
In the middle of a pant.
He may want to but he can't
The way I do with you.

[Verse 2] I'm the same as you are; tears come to my eyes
When I see professors chasing helpless butterflies.
Fishermen are hateful; they lead a wicked life.
Why, ev'ry day they separate some husband from his wife.

[Chorus 2] Never swat a fly.
He may love another fly.
He may sit with her and sigh
The way I do with you.
Never spray a nit
With a great big can of FLIT.
He may think some nit has "it"
The way I do with you.
Never stop a moth as he is gliding through the air.
He may have a date in someone's flannel underwear.
Be careful!
Don't you dare to slay
Two mosquitoes while they play.
They may want to make "hey-hey"
The way I do with you


There were other early recordings by:
Cotton and Morpheus, 1930-08-01.
Abe Lyman and His California Orchestra, 1930-09-17.
Allstar Californians, 1930-10-01.
Billy Uke Carpenter, 1930-10-01.
Varsity 8, 1930-10-14.
McKinney's Cotton Pickers, with vocal by Billy Coty, 1930-11-04.

Another chorus fragment collected from some recent recording:

Never take a chance
Treading on a pair of ants.
They may want that sweet romance
The way I do with you.