The male worm is smaller, 40 mm (1.6 in) long and 100 μm (0.0039 in) wide, and features a ventrally curved tail.

It appears quite structureless in vivo, but histological staining makes its primitive gut, nerve ring, and muscles apparent.

The cause of this periodicity remains unknown, but the advantages of the microfilariae being in the peripheral blood during these hours may ensure the vector, the nighttime mosquito, will have a higher chance of transmitting them elsewhere.

[citation needed] The microfilariae are transferred into a vector, which are most commonly mosquito species of the genera Culex, Anopheles, Mansonia, and Aedes.

Inside the mosquito, the microfilariae mature into motile larvae called juveniles; these migrate to the labium after a period around 10 days.

The larvae develop into adult worms over the course of a year, and reach sexual maturity in the afferent lymphatic vessels.

Ancient Greek and Roman writers noted the similarities between the enlarged limbs and thickened, cracked skin of infected individuals to that of elephants, hence the name elephantiasis to describe the disease.

[citation needed] In 1862 in Paris, Jean-Nicolas Demarquay [fr] found what appeared to be nematode worms in the fluid aspirated from a hydrocele in a young man from Havana, Cuba.

Unaware of this observation, three years later in Bahia, Brazil, Otto Wucherer [pt] found these same worms but this time in urine from a woman with chyluria.

Some of Lewis's specimens were examined in the same year in England by George Busk who named them Filaria sanguinis hominis.

[11] In 1876 and 1877, Joseph Bancroft in Brisbane, Australia found adult worms in lymphatic abscesses in patients with larvae in the blood.

In 1899, Thomas Bancroft in Brisbane fed laboratory-reared mosquitoes on a patient with microfilaraemia, kept them for 16 days, then sent some specimens to George Low in London.

[13] Once it was introduced to the New World, this filarial worm disease persisted throughout the areas surrounding Charleston, South Carolina, until its sudden disappearance in the 1920s.