Invertebrates
Vampire Moth
Calyptra thalictri · also called vampire moth
The vampire moth looks like a hundred other drab grey-brown moths, but the males of a few species have a startling habit — they land on a large mammal, drill through the skin with a barbed, hook-tipped tongue, and drink blood for up to 20 minutes. Females never do it, and the caterpillars just eat plants.
Overview
Vampire moths live in forests of central and eastern Europe and temperate Asia, expanding northward. About 4–5 cm wingspan and plainly patterned, the caterpillars eat meadow-rue, and adults feed on fruit juice — with males of this species also taking blood.
A tongue built to drill
Its proboscis is stiff, hook-tipped, and barbed, evolved for sawing into tough fruit skins — and just as able to puncture mammal skin.
A gift, not a meal
Only males drink blood, so the leading idea is that salt from the blood is passed to the female during mating as a nuptial gift for her eggs.
Status
The vampire moth is Not Evaluated, not threatened, and expanding its range northward as the climate warms.
Vampire Moth: common questions
Do vampire moths really drink blood?
Yes, but only the males of a few species, and the behaviour is uncommon and was first documented under controlled conditions. Researchers studying Calyptra thalictri found that male moths would land on a person's skin, work the tip of the proboscis back and forth to drill through the outer layers, and then feed on the blood that welled up, in some cases for 15 to 20 minutes at a stretch. Similar blood-feeding has been recorded in a small number of other Calyptra species. The bite is described as a sharp, persistent pricking sensation, and while it is startling and can be briefly painful, the moths are not known to transmit disease and take only a tiny amount of blood.
Why do only male vampire moths feed on blood?
The fact that only males of Calyptra thalictri have been observed taking blood, while females stick to fruit juice, points away from blood being a simple food source and toward a reproductive function. The leading hypothesis is that the male incorporates salt, sodium in particular, and other nutrients from the blood into the sperm package, or spermatophore, that he transfers to the female during mating. She then uses those resources when producing eggs, so the blood meal effectively becomes a nuptial gift that improves the male's reproductive success. This kind of male provisioning through unusual feeding is documented in several other insect groups.
How did a fruit-eating moth start drinking blood?
The vampire moths belong to a group whose members normally feed by piercing the skins of ripe and unripe fruit with a stiff, barbed, hook-tipped proboscis and pumping up the juice inside, a habit that already makes them minor agricultural pests. That mouthpart is essentially a tool for punching through a tough outer surface and drawing out liquid, and mammal skin presents a very similar mechanical problem. Researchers think the shift to occasional blood-feeding required only a modest change in behaviour rather than any new anatomy, since the moth was already equipped with the necessary drilling and pumping apparatus.
Is the vampire moth dangerous or spreading?
It poses no real danger to people. The blood meals are tiny, the moths are not disease vectors as far as is known, and encounters are rare, since blood-feeding is an occasional behaviour of a small number of individuals rather than a routine part of the species' life. The vampire moth is, however, expanding its geographic range, having been recorded well north of its historic distribution in Europe in recent decades, including in Finland, a shift consistent with the northward range expansions seen in many insects as the climate warms.