SO BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE 
DESTRUCTION BY BIRDS AND MAMMALS 
Birds undoubtedly destroy many larve as they drop to the ground 
after emerging from the backs of cattle. The pupz also are subject 
to attack, since they often remain exposed on the surface of the 
soil or only slightly covered. Several instances were observed 
in New York in which robins (Planesticus migratorius) devoured 
larvee of H. bovis with avidity. In one case a larva under observa- 
tion as it burrowed into the soil was seen by a robin sitting on a 
fence. The robin flew down, picked up the larva, and escaped with 
it before the bird could be frightened away. ‘This larva was almost 
covered by the soil as it burrowed in. Species of the larger ground 
birds undoubtedly destroy many larve. Henry Polson of Mountain- 
view, Wyo., makes the following statement: “ Sometimes magpies 
pick holes in the backs of the cattle, trying to get the grubs out, 
causing sores.” In rather extensive observations made by one of 
the writers in areas where magpies (Pica pica hudsonia) abound, 
this action has not been seen, hence it is thought to be rare. 
Many larve which emerge from cattle in the barnyards where 
poultry range are destroyed by fowls. Chickens have been observed 
to devour greedily considerable numbers of mature larve when fed 
to them. 
It is probable that small rodents destroy. many larve and pupe. 
Stegmann (94) states that the pupe on the ground are destroyed 
by moles. 
INSECT ENEMIES 
No predacious insects have been observed to attack the larve or 
pups of Hypoderma in the United States, and it is thought that 
they are not an important factor in control. 
No parasites have been found in nature, but very few pupe have 
been recovered after exposure in fields. The writers have reared a 
considerable number of specimens of Vasonia brevicornis Ashm. from 
pup kept in screen cages in an outdoor insectary, in more or less 
close association with parasitized pupe of muscoid flies. 
A, Gansser, of the Warble Committee of Switzerland, states in a 
letter that he thinks that a hymenopterous parasite which has not 
been determined is an important factor in control in that region. 
FUNGOUS GROWTHS 
The writers have observed the growth of molds on and in the 
puparia of Hypoderma, and there is some reason to believe that the 
insects may be attacked in some cases. Lucet (63) expresses the 
opinion that in France certian fungi destroy the pupe. 
EFFECT OF SUBMERGENCE ON LARVZ AND PUPZ 
In 1921 a considerable number of extracted larve of H. lineatum 
were submerged in water for periods ranging from 3 to 23 hours. 
These periods apparently had very little effect on the larve; at least 
the percentage found dead at the end of three days was not greater 
than in the untreated groups. During 1922 five mature larve were 
submerged from 114 to 19 hours. The larva submerged the shortest 
period produced an adult in normal time, but the four submerged 
