Both spikes and loose nets can be installed over nest sites to prevent the bird from returning, but nets are not a humane option since birds and other wildlife can get tangled in them. 

Spikes are a humane alternative that deter nesting without harming the birds. In small areas, like vents, a very fine mesh net can be installed to prevent the bird from returning. These nets don't generally pose a risk to the birds.

No, mothballs do not keep bats away. Not only are mothballs completely ineffective when repelling or removing bats, but using them could be illegal, depending on where you live. Remember, bats are federally protected, and it's illegal to use chemicals during the removal process, and mothballs tend to fall into this category.

Certain strong smells may help repel bats, though this is not a foolproof method and is best used in conjunction with other deterrence strategies. Scents like peppermint oil, eucalyptus, cinnamon, cloves, and mint are often suggested as natural remedies. To create a spray, you can mix two cups of warm water with half a cup of sugar and a few drops of your preferred essential oil. Apply this mixture using a spray bottle to possible entry points and throughout the affected area, such as an attic. While this home remedy is popular, evidence supporting its effectiveness is limited.

A treatment from a pest control service can last anywhere from 3 to 6 months, depending on the type of treatment, what pest it’s treating, and what environment you live in. This is why pest control service companies often offer packages where they come out multiple times a year to apply treatment to the outside or inside of your home.