July, 1892. 
THE NATURALIST IN LA PLATA. 
153 
in preventing accidental injuries to them from a few crepus¬ 
cular bats and goatsuckers. And to believe even this we 
should first have to assume that bats and goatsuckers are 
differently constituted from all other creatures; for in other 
animals—insects, birds, and mammalians—the appearance of 
fire by night seems to confuse and frighten, but it certainly 
cannot be said to warn , in the sense in which that word is 
used when we speak of the brilliant colours of some butter¬ 
flies, or even of the gestures of some venomous snakes, and 
of the sounds they emit. 
“ Thus we can see that, while the old theory of Kirby and 
Spence had some facts to support it, the one nowin vogue is 
purely fanciful. Until some better suggestion is made, it 
would, perhaps, be as well to consider the luminous organ as 
having ‘ no very close and direct relation to present habits 
of life.’ About their present habits, however, especially 
their crepuscular habits, there is yet much to learn. One 
thing I have observed in them has always seemed very strange 
to me. Occasionally an individual insect is seen shining 
with a very large and steady light, or with a light which very 
gradually decreases and increases in power, and at such times 
it is less active than at others, remaining for long intervals 
motionless on the leaves, or moving with a very slow flight. 
In South America a firefly displaying this abnormal splendour 
is said to be dying, and it is easy to imagine how such 
a notion originated. The belief is, however, erroneous, for 
sometimes, on very rare occasions, all the insects in one place 
are simultaneously affected in the same way, and at such times 
they mass themselves together in myriads, as if for migration, 
or for some other great purpose. Mr. Bigg-Wither, in South 
Brazil, and D’Albertis, in New Guinea, noticed these firefly 
gatherings; I also once had the rare good fortune to witness a 
phenomenon of the kind on a very grand scale. Biding on the 
pampas one dark evening an hour after sunset, and passing 
from high ground overgrown with giant thistles to a low plain 
covered with long grass, bordering a stream of water, I found 
it all ablaze with myriads of fireflies. I noticed that all 
the insects gave out an exceptionally large, brilliant light, 
which shone almost steadily. The long grass was thickly 
studded with them, while they literally swarmed in the air, all 
moving up the valley with a singularly slow and languid 
flight. When I galloped down into this river of phosphorescent 
fire, my horse plunged and snorted with alarm. I succeeded 
at length in quieting him, and then rode slowly through, 
compelled to keep my mouth and eyes closed, so thickly 
did the insects rain on to my face. The air was laden 
with the sickening phosphorous smell they emit, but when 
