This one's been bouncing around the internet for a while now - I've never seen a valid answer for it.
It might have had a real answer at some point, but my guess is it got mis-translated or corrupted somehow, going from person to person. I don't think this can be answered properly in this form.
This is the best I could find in an old Google Group posting:
> I am eleven letters long , my 1234 is an insect, my 345 is food,
> my 5678 is a heavenly body, my 91011 is your best friend . If you
> get my 1358 you'll get my 78910. What am I ?
My solution is
1 2 3 4 5 6 7 8 9 10 11
I K C E R S A T G O D
These letters don't seem to form a phrase but the problem didn't say they had to. An anagram of these letters is TRICK DOSAGE,
and this provides a vital clue;
one trick isn't enough; we must up the dosage to two:
IKCERSATGOD + TRICK
After adding in an extra TRICK (= RCT+I+K) I can solve all six clues:
``my 1234 is an insect''
1234 = IKCE + RCT = CRICKET
``my 345 is food''
345 = CER + I = RICE
``my 5678 is a heavenly body''
5678 = RSAT = STAR
``my 91011 is your best friend''
91011 = GOD = DOG
``If you get my 1358''
1358 = ICRT + K = TRICK
``you'll get my 78910''
78910 = ATGO = GOAT
Yes, I agree this is unsatisfactory, but I'll bet most of the words are right. (TICK is another likely possibility for Insect.) ``Your best friend'' is almost certainly DOG. (PAL would *not* be clued with ``best.'')
And, although word fits can arise by chance, STAR, and GOAT are *very* good fits making coincidence less likely.
