The different panorpa species apparently are practically impossible to separate in the field. But males can be identified by their genitalia, more specific the pattern of the hypovalves, showing as two lines on the underside of the genitalia that the male luckily always holds in a folded position, so that they can be seen from above if good photos are obtained. This site gives an idea about what to look for: http://www.wbrc.org.uk/WORCRECD/37/Averill_Mike--1_Identification_of_Scorpion_Flies.html.