I have seedlings started indoors in polystyrerne cups, under lights:
tomatoes & peppers up about 1 inch but not yet with true leaves. This
morning I find about 30 percent are nipped off 1/4 to 1/2 inch above
soil level. In most cases the young first leaves are gone. Completely
vanished - just a stub of stem remains.

I see no sign of whatever pest has done this (apparently overnight
when the lights are off.)

Can anybody make an educated guess, what beastie would this be? And
what can I do to protect the rest of my seedlings - please be quick! -
as well as thwart the pest in future?

Thanks,
Alexander Miller
Port Alberni, B.C. (Canada )