It seems, from what I’ve just been reading on the NatureSpot website, that I was very lucky to catch these Scorpion flies in flagrante delicto:

Mating usually occurs at night. It can be a dangerous time for the male, if he is not careful the female might decide to kill him! To avoid this he presents her with a gift of a drop of saliva which, it seems, in the world of scorpion flies, is the equivalent of a bunch of roses or a box of chocolates.