Truth is a special way of looking at life which is provided by the teachings of Divine Revelation. Truth is spiritual light. Falsity, on the other hand, is darkness. Another thing we must realize about falsity is that it is not simply a matter of perspective. It is also connected to what we love.
Falsity is the result of loving what is evil.
Of course, some basically good people have mistaken ideas. Such people, though, are not fully immersed in falsity. A person is only immersed in falsity when he loves what is evil, for then his whole outlook on life is distorted, and his whole mind is filled with darkness. And yet the falsities represented by locusts are not just falsities. The locust, which is nothing but a small and lowly insect, represents falsity which invades the lowest or sensual degree of the human mind.