Use of Cottony Secretions 177 
attending the honey-glands of the bull’s-horn acacia along 
with the ants, so at Santo Domingo another wasp, belonging 
to quite a different genus (Nectarina), attended some of the 
clusters of frog-hoppers, and for the possession of others a 
constant skirmishing was going on. The wasp stroked the 
young hoppers, and sipped up the honey when it was exuded, 
just like the ants. When an ant came up to a cluster of leaf- 
hoppers attended by a wasp, the latter would not attempt to 
grapple with its rival on the leaf, but would fly off and hover 
over the ant; then when its little foe was well exposed, it 
would dart at it and strike it to the ground. The action was 
so quick that I could not determine whether it struck with 
its fore-feet or its jaws, but I think it was with the feet. I 
often saw a wasp trying to clear a leaf from ants that were 
already in full possession of a cluster of leaf-hoppers. It 
would sometimes have to strike three or four times at an ant 
before it made it quit its hold and fall. At other times one 
ant after the other would be struck off with great celerity 
and ease, and I fancied that some wasps were much cleverer 
than others. In those cases where it succeeded in clearing 
the leaf, it was never left long in peace. Fresh relays of ants 
were continually arriving, and generally tired the wasp out. 
It would never wait for an ant to get near it, doubtless know- 
ing well that if its little rival once fastened on its leg, it would 
be a difficult matter to get rid of it again. If a wasp first 
obtained possession, it was able to keep it; for the first ants 
that came up were only pioneers, and by knocking these off 
it prevented them from returning and scenting the trail to 
communicate the intelligence to others. 
Before leaving this subject, I may remark that just as in 
plants some glands secrete honey that attracts insects, others 
a resinous liquid that repels them, so the secretions of 
different genera of the homopterous division of the Hemiptera 
are curiously modified for strikingly different useful purposes. 
We have seen that by many species of plant-lice, scale- 
insects, and leaf-hoppers, a honey-like fluid is secreted that 
attracts ants to attend upon them. Other species of aphides 
(Eriosoma) that have no honey-tubes, and many of the 
Coccidze, secrete a white, flocculent, waxy cotton, under 
which they lie concealed. In many of the Homoptera, this 
secretion only amounts to a white powder covering the body, 
