40 
HALF HOURS WITH INSECTS. [Packard. 
Fig. 30. 
they belong, such as the mealy bug of our hot-houses or 
Cochineal insect of tropical countries and the Aleurodes, in 
which the sexual differences are less marked, and then com¬ 
paring them with the aphides on 
the one hand, and on the other 
the Psylla, a member of another 
family closely allied, we are en¬ 
abled to see that the changes 
in form have been undoubtedly 
induced by differences in habits, 
the kind of surface to which the 
scales are attached, the species 
of tree to which they belong, as 
well as to the different degree 
of mobility of the female ; for the 
more she is fixed and immov¬ 
able, the more active and lively 
is the male, just as in Stylops 
or bee-parasite, the female 
(Fig. 30) is remarkably different from the agile, volant male 
(Fig. 31). We may see in the aphis, where the two sexes 
are alike, that in their 
courtships the male 
finds its active partner 
in the ordinary move¬ 
ments of life, while 
since the female scale 
insect is immovable, 
its winged partner 
needs to be far more 
restless and swift in 
its movements than 
the male aphis; so 
that its chances of encountering its mate in the course of 
its travels, and thus providing for the continuance of the 
8 
Female Stylops 
Fig. 31. 
Male Stylops. 
