Nature's Night Lights. 169 
standing this fact, and assuming that we have here 
the whole reason of the existence of the light- 
emitting power, a study of the firefly’s habits com- 
pels us to believe that the insect would be just as 
well off without the power as with it. Probably it 
experiences some pleasure in emitting flashes of 
light during its evening pastimes, but this could 
scarcely be considered an advantage in its struggle 
for existence, and it certainly does not account for 
the possession of the faculty. 
About the habits of Pyrophorus, the large tropical 
firefly which has the seat of its luminosity on the 
upper surface of the thorax, nothing definite appears 
to be known; but it has been said that this instinct 
is altogether nocturnal. The Pyrophorus is only 
found in the sub-tropical portion of the Argentine 
country, and I have never met with it. With the 
widely-separated Cratomorphus, and the tortoise- 
shaped Aspisoma, whick emit the light from the 
abdomen, I am familiar; one species of Crato- 
morphus—a long slender insect with yellow wing- 
cases marked with two parallel black lines—is “the 
firefly’ known to every one and excessively abun- 
dant in the southern countries of La Plata. This 
insect is strictly diurnal in its habits—as much so, 
in fact, as diurnal butterflies. They are seen flying 
about, wooing their mates, and feeding on composite 
and umbelliferous flowers at all hours of the day, 
and are as active as wasps during the full glare of 
noon. Birds do not feed on them, owing to the 
disagreeable odour, resembling that of phosphorus, 
which they emit, and probably because they are 
found to be uneatable; but their insect enemies are 
