Robberflies are aptly named! A bit like a highway man they lie patiently in wait and strike when an unsuspecting insect passes by. They have long, spiny legs to grip their victim and sharp piercing mouth parts to kill and consume it. Those jaws can inflict a painful bite in self defence if you attempt to handle one but they are not human biting insects otherwise, unlike mosquitoes fr example.
This particular species is the slender-striped robberfly (Leptogaster cylindrica). It has a long thin body, hence the 'slender' which has bands or 'stripes' around it. Being a robber fly it is thus named as the slender-striped robberfly!
This species is found on grasslands and hedgerows from May until August and is widespread and not uncommon in southern England but they are seldom seen by casual observers.Leptogaster cylindrica: the slender-striped robberfly