The Vampire Moth: this moth can pierce through the skin on a piece of fruit and suck the juices from within, and it has been known to use the same tactic to feed on human blood
Moths of the genus Calyptra are commonly known as vampire moths, thanks to their bizarre feeding habits. They are obligate fruit-piercers, meaning that they primarily feed on fruit, using a specialized proboscis to pierce through the skin and then extracting the fluids from within, but at least 10 species of Calyptra moth (out of 18 in total) also use that technique to feed on the blood of living vertebrates, including humans.
Above: close-ups of two moths from the genus Calyptra
Vampire moths have also been known to feed on the blood of cattle, pigs, deer, water buffalos, antelope, and elephants, among other things.
In order to extract the blood from its host, the moth presses its proboscis against the animal's skin and then oscillates its head back and forth until it penetrates the surface. Then, according to this article:
As blood from the host animal wells up, it opens hooks on the sides of the proboscis to anchor it firmly. The proboscis has two parts that alternate between anchoring and drilling through host tissue using an “antiparalell” movement.
A bite from a Calyptra moth is red and sore, but is believed to pose no danger to human beings.
Above: the tip of a vampire moth's proboscis, showing the hooks that assist in piercing the skin of both ripened fruit and living mammals
Calyptra is a widely distributed genus that can be found on most continents, but blood-feeding behavior (also known as hematophagy) only seems to occur in populations that inhabit certain parts of Southeast Asia and Northern or Eastern Russia.
Some of these moths feed on blood only when they're located in certain parts of their geographical range, and then exclusively feed on fruit throughout the rest of their environment. Researchers speculate that those habits might be connected to differences in elevation, precipitation, or some other macroclimate conditions.
Above: Calyptra minuticornis
Hematophagy occurs almost exclusively among the adult males of this genus. The biological purpose is unclear, but many scientists believe that it allows the males to supplement their sodium intake as they prepare to transfer nutrients to the females during reproduction.
Above: another Calyptra moth
Vampire moths are also excellent leaf mimics; their wing-pattern, color, and resting position all strongly resemble the appearance of a dry, curled-up leaf, which allows them to blend in with their environment.
Acts & Facts: Rogue Moths Didn't Start Out that Way
Purdue University: Investigations of the Vampire Moth Genus Calyptra (PDF)
Journal of Vector Ecology: Blood, Sweat, and Tears: a Review of the Hematophagous, Sudophagous, and Lachryphagous Lepidoptera
Medical and Veterinary Entomology: Wound-Feeding and Skin-Piercing Moths (PDF)
Entomological Society of America: Geographic Distribution and Differential Feeding Behaviors of Calyptra thalictri
Entomology Today: Vampire Moths Suck the Blood of Vertebrates, Including Humans
Nikon Small World: Photo of Calyptra thalictri Proboscis
The Daily Garden: Vampire Moths
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