Most pests run away from smells they don't like. In most cases, a light spray with their most dislike
d pong is enough to keep them away. Here are some tried and true formulas to deter the most common household pests.
Fleas, Bees and Wasps
Place six teaspoons of dried common mint (not peppermint tea) in a teapot full of boiling water. Leave to steep for about 15 minutes and strain into a spray bottle. Spray lightly over your pet's beddin
g to keep fleas at bay.
After wasp nests or beehives have been removed, spray the area with this mint tea to prevent the insects from returning and building a new home.
Weevils (pantry moths) 
Place 12 dried bay leaves in one cup of boiling water. Leave to steep for about 15 minutes and strain into a spray bo
ttle. Use this spray to clean down the shelves in your pantry.
Afterwards, placing one dried bay leaf every 60cm along the pantry shelves will break the weevils' breeding cycle and eradicate the problem over time.
Flies and Mosquitoes
M
ix one teaspoon of lavender oil with one litre of water in a spray bottle. Lightly spray the solution onto a cloth and wipe the cloth over all doorjambs and window frames to keep flies and mosquitoes out of the house.
This can also be used as a personal insecticide — just spray it lightly over the skin.
Slugs, Snails, Slaters, Centipedes, Millipedes and Mice
Mix one teaspoon of Vicks Vapo Rub with one litre of boiling water in a spray bottle. Lightly spray around doors, windows and drains to keep all these critters out.
Wardrobe Moths
Simply place a small bowl of cedar chips in your wardrobe to keep moths away. Silverfish If silverfish are present in your carpet, place one whole clove at 1m intervals along the skirting boards. If they are in your wardrobe, a couple of cloves on each shelf will do the trick.
Spiders
Stuff the head of a soft kitchen broom down the leg of a pair of pantihose and tie the excess leg material around the broom handle.
Wipe just two drops of lemon oil across the head of the broom and start sweeping away 
those cobwebs.
This treatment lasts for several months; you'll be able to tell when the effects of the lemon oil are wearing off because you'll notice new cobwebs appearing around the house.
Images from Microsoft Office and Wikipedia.