Here are some photos of eggs deposited on the underside of leaves. ID would be great. A search resulted in one person saying they suspected a moth. It would be a huge moth because numerous leaves received eggs. In addition to the eggs, a lot of gossamer threads were present, almost as thick as cotton. I believe the caterpillars hatch and parachute away on these threads. I've sprayed the area with BT, Bacillus Theringiensis, to kill the caterpillars.
Why kill the caterpillars.?
The caterpillars damage the plant and leave their poop behind. As these plants are intended for consumption, the presence of caterpillars is minimized. It seems the moths and butterflies can 'smell' the presence of the bacteria, and fly to more promising food sources. The bacteria are harmless to humans.