Airplane wings are pretty strong!

[KillerCharlie]

Boeing makes the 57 and 67 lower wing skin/spar at a plant a few miles from my house. I worked on the construction of the facility back in 1991.
The lower wing skin and spars are milled from one single block of aluminum.
This saves time in assembly, but the big savings is in maintenance and sealing of the tanks.

Ehh... they're more like sheets instead of "blocks." They only do that to get the right thickness, then they form them to the right shape. Pretty much all commercial airplanes have single piece spars.

 

[LTC8K6]

http://www.youtube.com/watch?v=pe9PVaFGl3o

Modern airliner wings are incredibly strong and flexible.