F1 
Farmers’ Bulletin 1150. 
G. 382.—Thread lungworms (Dic- 
tyocaulus filaria). Male at right; 
female at left. Highly magnified. 
(From Curtice, 1890.) 
THE THREAD LUNGWORM.”” 
Location—The thread lungworm ~ 
is found in the air passages, bronchi 
and bronchioles of the lungs. 
Appearance.— These are rather 
long worms, easily observed. They 
are white and the intestine shows as 
a dark hair line throughout the 
length of the worm (fig. 32). The 
male is 3 to 8 cm. (from more than 1 
inch to more than 3 inches) long. 
The female is 5 to 10 cm. (2 to 4 
inches) long, with a straight, conical 
tail. The eggs contain an embryo 
when they leave the body of the 
mother worm. 
Life history—The eggs deposited 
by the female hatch in the lung of the 
host animal, probably in the course 
of 24 hours, and are expelled in 
coughing, or swallowed and passed 
in the feces. The newly hatched 
larva has a rounded head and a rather 
blunt tail. It molts twice in the 
course of the next few days, the time 
varying with temperature and mois- 
ture, and, under ordinary circum- 
stances, is infective within 10 days. 
This larva then climbs up grass 
blades, when they are wet and the 
weather is warm, as does the larva of — 
the stomach worm and thread-necked 
worm, and here it is taken in by graz- 
ing sheep and makes its way to the 
lungs. In the course of a month the 
sheep begin to show symptoms of 
lungworm, and in about five weeks 
embryos appear in the manure. 
Distribution.— These worms are 
widely distributed over the world 
and are comparatively common in the 
United States, especially in the South 
and where there is plenty of moisture 
and warmth. 
22 Dictyocaulus filaria. Synonym, Strongylus filaria, 
