Thus we can see that, while the old theory of Kirby and Spence had some
facts to support it, the one now in 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. Riding 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