In many cases the biting habits of blackflies (Diptera: Simuliidae) are associated with transmission of pathogens such as the protozoan Leucocytozoon spp. to birds and Onchocerca spp. to mammals, including Onchocerca volvulus the causative agent of human onchocerciasis or 'River blindness' (Brattig et al., 2021). Even if they do not transmit pathogens the extent of blackfly biting can be an intolerable nuisance to people and livestock. But on the other hand, they are also an important link in the trophic chain of environments associated with rivers and streams, where they form part of the diet of other macroinvertebrates, as well as of various species of both aquatic and terrestrial vertebrates. In addition to transmitting Onchocerca spp. to cattle, several species of Simuliidae are known to cause other veterinary problems in the UK such as 'sweet itch' which affects horses and cattle, as well as being biting nuisances to people, sometimes causing intense itching and allergic reactions. A means of monitoring and perhaps controlling them arose in 2017, when it was noticed that numerous adult females of Simulium spp. were caught in Mosquito Magnet traps (Fig. 1) set in various parts of the UK primarily to catch adult female mosquitoes (Cheke et al., 2018). During 2018 and 2019 additional samples of blackflies were obtained from such mosquito traps at numerous sites including some deployed by entomologists working for the UK Health Security Agency (then known as Public Health England) (López-Peña et al., 2021). Amongst the catches were many S. equinum, known to be responsible for 'sweet-itch', so it was important to determine where they were breeding in relation to the trap catches. So, in 2020 we surveyed rivers near many of the catching sites and we also checked a selection of other aquatic habitats in southern England to study the ecology of immature stages of the blackflies, results of which were reported by López-Peña et al. (2022). During that study, photographs of larvae and pupae were taken, some of which are presented here in a short review of aspects of the biology of the various species of blackfly that are of veterinary or public health importance, with comments on their parasites and predators. These sections are preceded by a list of the known British species, together with geographical distribution maps of many of them supplied by the National Biodiversity Network Atlas (NBN, 2023).