Do Mammals or Insects have the largest Range of Masses? Conclusion: Mammals!

 https://en.wikipedia.org/wiki/Etruscan_shrew

1.8g avg

https://en.wikipedia.org/wiki/Blue_whale

200tons ==450g/lb *2000lb= 180,000,000g == 1.8x10^8gm


ratio: 1:0^8

large beetles
https://web.archive.org/web/20140820232404/http://entnemdept.ufl.edu/walker/ufbir/chapters/chapter_30.shtml

It is not easy to find reliable weights of insects, also apparently they can considerably bulk up in a day's feeding!  
lets call it 50g

fairy wasp:
https://animaldiversity.org/accounts/Dicopomorpha_echmepterygis/

0.2mm  no reported weights.

lets approximate mass pretending they are same density as water.

0.2mm^3 *1cc/1000mm^3 *1g/cc == 0.002mm^3/1000 = 0.000002g
probly an overestimate.

ratio
50g/0.000002g
==25 *10^6/ 0.000002g *10^6
2.5x10^7/2
1x10^7:1

10^7:1

mammals win by a factor of 10