Garlic and Cayenne Pepper spray
A homemade pepper spray can kill spider and dust mites quite effectively. Make use of 2 cups of chopped hot peppers, one tablespoon of cayenne peppers and 2 or 3 garlic heads, 3 teaspoons of liquid soap (dishwashing liquid) and make a puree of all these ingredients. Then mix this puree in 4 gallons of water taken in a bucket. Let the concoction sit in water for at least 24 hours. Strain the mixture into spray bottle and spray around your home and garden every month to create a bug-proof barrier.