Insects in Space is a side-scrolling shooter with similarities to Defender. Insects killed everyone on Earth except a few babies. This causes the mystical leader of motherhood, St. Helen, to travel to Earth's remains and save the babies. The most important feature of this protagonist is the fact that she is topless and - as prominently mentioned in the manual - "big breasted", but she controls and shoots just like the space ship normally found in those games.
The levels are side-scrolling and St. Helen can move in both directions. Additionally the levels are two screens high, the lower with a floor and the higher with a ceiling, which can be changed by leaving the current screen to the top respectively bottom. The babies are either positioned at the top or bottom level and are hunted by bees. Those bees pick them up, steal their life energy to create a new monster and drop them to the ground to die. The player's job is to kill the bees and save the babies. To help, a radar shows where in the level a kidnapping is in progress. Babies can be either returned to the ground for points or kept in Helen's grasp to convert them into power-ups eventually. Helen can also summon a dust cloud which teleports her near a bee target.