Lurking in the forests of Transylvania flies a strange and unsettling species of otherwise unremarkable moth, Calyptra thalictrii. Belonging to the widespread group of moths, the Noctuiidae, this species until recently lived as an adult on the juices sucked from fruit, like the other members of its genus. However, at some point it changed its diet, and now is known to feed on blood, even that of humans.
To be fair, there are other species of moth which also feed on blood, although feeding from the tears or sweat of mammals is far more common in lepidoptera – even in our own butterfly house the Glasswings will often land on people to feed on their sweat (this is especially true if they have been eating chips – they are attracted by the salt). The Asian Vampire Moth Calyptra eustrigata, even attacks elephants!
It is good to know that the vampire moth rarely attacks humans, and as far as is known only males have been observed feeding on blood. The reason for this difference between males and females is unclear, but in many species of butterfly and moth the males accumulate compounds from their food to be used as pheromones in courtship, so possibly something similar is happening here.
The caterpillar of the vampire moth feeds on meadow rue, Thalictrum, which is a very widespread European plant. I have not been able to find out anything about the flight season, which may vary with the location, but the related Calyptra canadensis from North America (including Canada) flies from July onwards and probably overwinters as an egg.
Until recently, vampire moths were restricted to south east Europe and further east, as far as Japan, but whether they feed on blood throughout their range is unclear. What is clear is that they have been spreading north and west in recent years, and have now reached Sweden and Finland. Given their distribution, I suspect the UK may not have the right climate (too wet) for a breeding population to establish itself here, but stranger things have happened. So if a moth suddenly starts paying attention to you – watch out!