Midges are tiny swarming insects that are common in the Scottish Highlands during the summer months. They are normally active at low light so are typically seen around sunset. Bites from midges do not transmit disease but can make life almost unbearable. Citriodiol® based repellents will help stop midges from biting but not from swarming around you. Covering skin with clothing will also help prevent being bitten as midges can't bite through material, and light clothing is preferable to dark. They can get under clothes so you could avoid them with more protective methods such as anti-midge hats, midge body suits and midge netting (smaller than mosquito nets) to cover tent entrances.
It is advisable to note the periods and conditions when midges are most active, and avoid being outside during these times. Calm, still windless summer evenings are when midges will be most active. They struggle in windy conditions and tend to stop flying. It is also important to try to avoid wet, boggy areas which are common breeding sites for midges. As midges are less common at heights (above 700m), try to get to higher ground.