Title: Hematophagy
Content:   Hematophagy (sometimes spelled haematophagy or hematophagia) is the practice by certain animals of feeding on blood (from the Greek words αἷμα haima "blood" and φαγεῖν phagein "to eat"). Since blood is a fluid tissue rich in nutritious proteins and lipids that can be taken without great effort, hematophagy is a preferred form of feeding for many small animals, such as worms and arthropods. Some intestinal nematodes, such as Ancylostomatids, feed on blood extracted from the capillaries of the gut, and about 75 percent of all species of leeches (e.g., Hirudo medicinalis), a free-living worm, are hematophagous. Some fish, such as lampreys and candirus, and mammals, especially the vampire bats, and birds, such as the vampire finches, hood mockingbirds, the Tristan thrush, and oxpeckers also practise hematophagy.
Title: Hemiptera
Content:  A few hemipterans are haematophagic (often described as "parasites" ), feeding on the blood of larger animals. These include bedbugs and the triatomine kissing bugs of the assassin bug family Reduviidae, which can transmit the dangerous Chagas disease. The first known hemipteran to feed in this way on vertebrates was the extinct assassin bug Triatoma dominicana found fossilized in amber and dating back about twenty million years. Faecal pellets fossilised beside it show that it transmitted a disease-causing Trypanosoma and the amber included hairs of the likely host, a bat.
Title: Hemichromis lifalili
Content:  These fishes mainly feeds on worms, crustaceans, insects, small fish, but also on vegetable matter.
Title: Hematophagy
Content:  instance, that they pre-inject—and anesthesia and capillary dilation have evolved in some hematophagous species. Scientists have developed anticoagulant medicines from studying substances in the saliva of several hematophagous species, such as leeches (hirudin). Hematophagy is classified as either obligatory or facultative. Obligatory hematophagous animals cannot survive on any other food. Examples include Rhodnius prolixus, a South American assassin bug, and Cimex lectularius, the human bed bug. Facultative hematophages, meanwhile, acquire at least some portion of their nutrition from non-blood sources in at least one of the sexually mature forms. Examples of this include many mosquito species, such as Aedes aegypti, whose both males and females feed on pollen and fruit juice for survival, but the females require a blood meal to produce its eggs. 
Title: Larval hemolymph feeding
Content:  haemolymph. are exclusively dependent on the hemolymph of their own larvae as a nutrient, even when prey feeding is possible. On the other hand, the foundresses suppress larval hemolymph feeding (LHF) when prey is available, allowing them to rear the first workers more swiftly. The nondestructive form of cannibalism can be regarded as a nutritive adaptation related to: (1) the lack of social food transfer in this species, and (2) its specialized predation on large sporadic prey (centipedes). LHF similar to that in Amblyopone was found in Proceratium and another type of LHF, with a larval specialized exudatory organ, in Leptanilla.
Title: Hermosita
Content:  Both species of Hermosita feed on the hydroid Solanderia; a characteristic shared with the Pleurolidiidae.
Title: Larval hemolymph feeding
Content:  Larval hemolymph feeding is a behaviour trait found in the queens of some species of ant. This is found mainly in the ants of the subfamily Amblyoponinae and give them the other name of Dracula ant. In colonies of the Amblyopone silvestrii the queens feed on the hemolymph (or insect blood, also spelt haemolymph) of their larvae when food is not available. This is said to be a precursor to trophallaxis in other ant families. The larvae themselves are not killed by this process. This behaviour is also seen in Proceratium and in Leptanilla the larvae have special organs that exude 
Title: Hemibdella soleae
Content:  H. soleae is an ectoparasite of flatfish such as the common sole (Solea solea). Like other marine leeches, it feeds on its host's blood, but unlike most freshwater species, it does not drop off the fish after it has fed, instead remaining attached by its anterior sucker. In the juvenile leech, the remnants of each blood meal is visible through the transparent skin as a small red ball inside. In the northern part of its range, the common sole is the main host, but further south, other fish are also parasitized; these include the Senegalese sole (Solea senegalensis), the wedge sole (Dicologlossa cuneata), the bastard sole (Microchirus azevia), the Klein's sole (Synapturichthys kleinii), the sand sole (Pegusa lascaris) and the Portuguese sole (Dagetichthys 
Title: Helogenes
Content:  Helogenes species feed on allochthonous insects. The only species for which details of the ecology are known is H. marmoratus (refer to article for that species).
Title: Lutzomyia longipalpis
Content:  Although the feeding of blood is important for the maturation of oocytes, too many blood meals can also negatively impact the lifespan of females. Lutzomyia Longipalpis, like most other blood-sucking organisms, ingest large amounts of blood in a single meal. A female sandfly consumes between three and ten times its body weight in one feeding. Blood is rich in proteins, consisting mainly of hemoglobin (Hb), which accounts for approximately 60% of the blood protein content. The digestion of hemoglobin results in the release of high levels of the prosthetic group heme. Heme acts as a toxic molecule that can generate oxygen-reactive species and bypass membranes due to its high permeability. Elevated levels of heme in female L. longipalpis are suspected to be the cause of increased mortality for females that have ingested multiple blood meals.

Question: which of the following helmiths feeds on blood?
Answer: Necator americanus.
Ancylostoma duodenale.