First we must identify the bottomless pit.  In other translations it uses the word Abyss; an abyss is a bottomless pit, or also a chasm that may lead to the underworld or hell.  According to the Jewish encyclopedia it is the place of punishment of the wicked; hell; the abode of certain demons.

The Locusts

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.  Revelation 9:3

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.  Revelation 9:5-6

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. Revelation 9:7-10

For their power is in their mouth, and in their tails: for their tails were like unto serpents, and had heads, and with them they do hurt.  Revelation 9:19

Description:

Shaped like horses

Crowns like gold

Faces of men

Hair like women

Teeth like lions

Wings

Tails like scorpions

Tails like serpents with heads

The locusts from the bottomless pit are demons.

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. Revelation 9:11