54 The Essex Naturalist Pipistrelle Pipistrellus pipistrellus (Schreber, 1774) The commonest species in Essex, this, our smallest bat, forms summer roosts in modern houses and is widespread throughout the County. It can be easily observed feeding in gardens, parks, along hedgerows and by rivers and is the bat most frequently observed during bat walks. Recent research has shown that there are two species of Pipistrelle, separately identifiable on the bat detector at