Of what value are spiders?

I got a fun book at the goodwill today (50% off day!) called "The Little Quiz Book" (©1956). 

You guys know i am a sucker for illustrations like this, and I think they'd be perfect for Gocco cards or something (what's the statute of limitations for stuff like that? are they considered to be in the public domain yet? i haven't been in college for 11 years so i can't remember...).

The book contains answers to fascinating questions, such as "Is the Black Forest in Germany really black?" and "Who was the first President to travel under water in a submerged submarine?" (In case you're wondering, no and Harry S. Truman). I also scored some cute vintage drinking glasses and a few other novels.

And if you're wondering of what value are spiders? They destroy countless millions of noxious insects each year, --flies, mosquitoes, bugs, and grasshoppers.