I have never had a problem before with things eating my bean plants, aside
from an occasional hole here, a nibble there. But today I went out and
found nothing but veins left on three of my smaller bean plants and my
watermelon plant.

i have had the same problem for a couple of years.... one day the plants are
healthy and growing well, the next day, nothing but lace work for leaves....
my wife went to the local homecenter and asked..... while i can't remember the
name of the bug that causes this type of problem, they did recommend a soap
insecticide:
SAFER (brand name)
Insecticidal Soap...
i bought it at Home Depot... once when the plant leaves were just poking thru
the ground and then after they are about 6 inches tall...... and then every
3rd or 4 weeks..... so far, it has worked well.... leaves are dark green and
climbing up the trellis....
hope this helps.....