It's not how big they are that counts,  it's the number of friends they invite along to the feast . 

Initially attracted by carbon dioxide exhaled on your breath, when they bite they release a chemical which is an invite to all other midges that they have found someone tasty.  They'll descend upon you in their millions.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html