This is just rough, I'd transpose it to whatever key is comfy for you...the D chords
with () are kinda optional, I played it with the (D) and without the (D) and both sound
Just discovered Melanie, and I loved this song and couldn't find the tabs, so I figured 
out, and thought I'd share it. Its a cute song, hope you enjoy it...

Alexander Beetle
Melanie

G               C
I had a little beetle
C       (D)             G
So that beetle was his name
C                  G
And I called him Alexander
       D                G
And he answered just the same
G                    C
And I put him in a matchbox
    (D)               G
And I kept him all the day
C                (D)     G
But nanny let my beetle out
C                (D)     G
Yes nanny let my beetle out
C                     (D)  G
She went and let my beetle out
D              G
And beetle ran away

Its the same for all the other verses, I think, here's the lyrics

She said she didn't mean it
And I never said she did
She said she wanted matches
And she just took off the lid
She said I mustn't worry
And I really mustn't mind
That there's lots and lots of beetles
The she's certain we could find
She said I mustn't worry
But it's difficult to catch
An excited sort of beetle
You've mistaken for a match

If we looked in all the places
That a beetle might be near
And we made the kind of noises
That a beetle likes to hear
And I heard a kind of something
And I gave a sort of shout
It was a beetle house
And Alexander beetle coming out
It was Alexander beetle
I'm as certain as can be
And he had that kind of look as though
He thought it might be me

And he had that kind of look as though
He thought he ought to say
"I'm really very sorry that I tried to run away"
And nanny's very sorry too
Cause you know what she did
And she's writing Alexander
Very blackly on the lid
So nan and me are friends because
It's difficult to catch
An excited Alexander
You've misstaken for a match