I puzzled long and hard over this.
A moon-faced apparition materialises out of the smoke ascending from an open door, on the left are things that look like featureless birds in flight, on the right is an all but indescribable horror with teeth.
So I went back to the Book of Revelation.
And I'm now fairly sure that the artist was having a go at visualising this passage- Rev 9: 1-11.
And the fifth angel sounded, and I saw a star fall from heaven unto the earth: and to him was given the key of the bottomless pit.
And he opened the bottomless pit; and there arose a smoke out of the pit, as the smoke of a great furnace; and the sun and the air were darkened by reason of the smoke of the pit.
And there came out of the smoke locusts upon the earth: and unto them was given power, as the scorpions of the earth have power.
And it was commanded them that they should not hurt the grass of the earth, neither any green thing, neither any tree; but only those men which have not the seal of God in their foreheads.
And to them it was given that they should not kill them, but that they should be tormented five months: and their torment was as the torment of a scorpion, when he striketh a man.
And in those days shall men seek death, and shall not find it; and shall desire to die, and death shall flee from them.
And the shapes of the locusts were like unto horses prepared unto battle; and on their heads were as it were crowns like gold, and their faces were as the faces of men.
And they had hair as the hair of women, and their teeth were as the teeth of lions.
And they had breastplates, as it were breastplates of iron; and the sound of their wings was as the sound of chariots of many horses running to battle.
And they had tails like unto scorpions, and there were stings in their tails: and their power was to hurt men five months.
And they had a king over them, which is the angel of the bottomless pit, whose name in the Hebrew tongue is Abaddon, but in the Greek tongue hath his name Apollyon.
The thing in the middle is the sun being obscured by the smoke of the pit, the things on the left are locusts (the 20th century painter left them featureless because he/she couldn't figure out what they were)- and the nightmare creature on the right- who corresponds in most details to Johns description of a locust- is Abaddon.