This proverb compares the behavior of wicked people to that of the gyrin (a type of aquatic insect). They act without regard for the judgment of others. When they are visible, they have no shame in their bad actions; and when they disappear, they do not blush with guilt. In other words, wicked people never concern themselves with morality or the opinions of others. The equivalent proverb in English would be ‘The devil never shies away from doing evil.’