OK, Interesting thread. On the relevance of nasties i.e bugs and biting insects etc, they all have a place in both the evolutionary cycle and the food chain. Remove something from the environment, and it will eventually damage something else, but if we are to agree that there is intelligence behind creation and not just random accidents, then everything is thought created, that being slightly different to a thought form. Thought forms are weak and transient, thought creations are semi-permanent and stronger.
I come from an esoteric study background, and among other things run courses on visualisation, mainly with regard to meditation and pathworking, but the techniques can be beneficial in the physical sense too.
Look about you, everything you see started in someones imagination, the car you drive, the chair you sit on, even you and me, we all started in someones imagination.
If you can imagine it, and then visualise it you can create it! We are all made in our creators image, so we are all at least demi-gods in a sense. We all move down the Qabalistic tree of life from Kether (ultimate potential) through Binah (understanding) where through force we receive form.
Elementals are thought created beings, we create them all the time, mainly they are weak and shadowy and soon disperse, children, with there unfettered imagination do it all the time, imaginary friends etc. but when they grow up and no longer need their imaginary friend it again fades away, back into the magikal elements from which it was created. Elementals, if consciously created are for a spesific purpose, and when the purpose is fulfilled they cease to exist, but if, when one is created the purpose was not specific, or if some thing prevented the being from completing its task, it will continue to exist more or less for ever. These beings inhabit the lower astral, and observe the behavior of humans,and try to emulate them, after a period of many years they may begin to develop an intelligence, perhaps that of a monkey, but they can never have a divine spirit as they are not part of the divine creation. It is these beings which are most commonly communicated with via a ouja board, and they can be very dangerous if they are allowed to enter our world, they can attach themselves to people and cause many problems, they are also very difficult to send back to the lower astral. there is a Chinese saying, 'when you are confronted by your demon, look into the past to when you created it, then enter its world and destroy it, if you allow it to enter your world it will destroy you!'
These elemental beings can also be created and used in curses and other occult works.
Most 'ghost hunters' come into contact with these beings as often the ghost hunts are in places of dubious atmospheres, e.g, old prisons, asylums, workhouses etc. where the inhabitants were not always of sound mind, and almost certainly were giving off negative energy and thoughts.