138 LETTERS ON ENTOMOLOGY. 
LETTER XIII. 
MY DEAR HARRIET, 
It is not day alone which presents 
to our view the wonders and beauties of creation ; 
there are many insects which adorn the dark 
robe of night with their diamond lustre ; and in 
hot countries, where evening is the season of 
activity or pleasure, they are as useful as they 
are beautiful. I allude to those insects which 
are furnished with a luminous secretion, incapa- 
ble of burning, though affording a very vivid 
light. The glow-worm, which is a connnon and 
beautiful example, resembles a caterpillar, but 
is, in reality, the perfect female of a winged 
beetle, which in many instances, particularly in 
Lampyris splendidula and L. hemiptera, is adorned 
with two or four luminous spots, which are seen 
when flying, though not always, as they have 
the power of withdrawing them from sight. 
The females also have the same faculty, which 
is necessary for their safety, and probably ac- 
counts for their not being always found in places 
where they usually abound. The light proceeds 
