9) LEAFLET 152, U. S. DEPARTMENT OF AGRICULTURE 
Stages of Development 
All fleas pass through four stages, the adult, the egg, the larva, or 
maggot, and the pupa, or resting stage. The adults are found on 
animals or hopping about on the ground. The eggs are laid by the 
| females while on the host and drop 
to the ground and hatch in a few 
days into legless larvae or maggots 
(fig. 4). In 2 weeks or more the 
larvae become full-grown in the dust 
or sand and then spin tiny cocoons, 
in which they change to adult fleas 
in the course of 1 or more weeks. 
Fleas often breed in tremendous 
numbers in basements or outbuild- 
ings where dogs, cats, or hogs are 
\ kept. Even when dogs, cats, and 
ex A other hosts are taken away, the flea 
ySN maggots proceed with their develop- 
~\ ment, and the resulting adults may 
live for several weeks without food. 
This accounts for the frequency 
with which people find their homes overrun with fleas when they return 
from a summer vacation. 
FIGURE 2.—Human flea (female), greatly enlarged. 
Control of Fleas on Animals 
Dogs and cats can be kept practically free of fleas by occasionally 
applying derris powder next to the skin along the back and neck 
and on top of the head. If animals have free run, this treatment 
must be repeated every 2 weeks. A level 
teaspoonful is enough to kill every flea on a 
large dog. For smaller animals the amount 
should be reduced according to the size of the 
animal. Most derris powders are effective. 
Their insect-killing value depends largely on 
the amount of rotenone they contain. They 
should have at least 0.5 percent of rotenone. 
Much of the derris powder now on the market 
contains 4 or 5 percent of rotenone. This 
may be diluted with taicum powder so as to 
bring the rotenone content down to 1 percent. aes ae ge 
Derriskillsslowly ; donotexpecttoseethefleas create onlareed Saas 
drop off deadimmediately after an application. 
If derris is not at hand, fresh finely ground pyrethrum powder 
(insect powder) may be used as a dust. Pyrethrum powder should 
contain not less than 0.9 percent of pyrethrins; these are the insecti- 
cidal principles of pryethrum. 
Neither derris nor pyrethrum is considered poisonous to domestic 
animals, although cats are sometimes thrown off their feed by licking 
the material from the coat. 
In areas where the human flea abounds, in addition to treating the 
dogs and cats as outlined above, hogs should be kept from barns and 
