The photograph shows men of the 15th battalion Highland Light Infantry. Despite the name, most recruits came from Glasgow. The 15th were famous as "the dandy boys in Green", all drivers and conductors of Glasgow's "shoogly trams". The rush of recruits caused a severe shortage of army uniforms so the "dandy boys" simply wore their green Glasgow trams uniforms!
This source highlights key factors which caused the rush of voluntary recruitment in Scotland between July and October of 1914. Why did so many volunteer?
Patriotism and Pride: Many volunteered because of their pride in Scotland and Britain. They were proud of and determined to defend the British Empire. Pride in their local communities was important too especially for the Glasgow Tramcar boys and other "Pals" battalions - all recruited from the same communities, the same Scout and BB companies and even the same families.
Escape: The Tramcar boys had a good employer in Glasgow City Corporation (Council) but many workers did not. Volunteering for the army was an escape from the grind of boring, low paid jobs and unemployment. Scotland had a very high rate of volunteer recruitment for this reason. When conscription was introduced in 1916, many Scots workers were NOT forced to join the army since their jobs, e.g. engineering / munitions, were often considered of vital national importance. Despite this fact, voluntary recruitment remained high in Scotland.
Proving yourself worthy: The "warrior race" myth had a powerful effect on young minds especially if they were subjected to pressure from employers (some landowners offered to keep jobs open for volunteers for when they returned), girl friends (some women gave white feathers to young men who were not in uniform) and relentless pressure from the media ...
Finally, many Catholic Scots (mostly first or second generation Irish immigrants) saw military service as a good way of proving their loyalty and defending fellow Catholics in Belgium and France.