The organisms were presented on planet Thanatos VII when a newly developed interphasic fusion process was used to build a warp core conduit, which inadvertently attracted the creatures. Being able to survive within the plasma conduit, the organisms infected the starship Enterprise when the device was installed. Besides attaching themselves to the crew and physically damaging the warp system, the organisms also emit an interphasic pulse which interfered with the workings of Data's positronic brain, causing him strange dreams and hallucinations. Fortunately, as they find out, the parasites can be destroyed by an interphasic pulse of high frequency.