824 
ANNUAL REPORT OP NEW YORK 
HESSIAN FLY. FLAX-SEED STATE. PUPA. 
this pressure, and if they received no more important molesta¬ 
tion than this, would not he apt to perish as they do. 
After the worm or active larva has fully completed its growth 
a slight diminution in the dimensions of the inner soft parts of 
its body commences, in which the tougher outer skin does not 
participate, but retains its full size. The result of this contrac¬ 
tion is, that the worm gradually cleaves from its outer skin. 
Examined with a magnifying glass when this change has recently 
commenced, a slight translucent space is observable at the head 
end, and a larger and more obvious one at the pointed or tail 
end, plainly indicating that the enclosed worm does not entirely 
fill its outer skin. This contraction continues, until the worm 
becomes entirely separated from its outer skin, and lies within it 
like the finger within a glove. The outer skin at the same time 
changes in color. From its original whiteness and transparency, 
it now becomes opake, brown, and finally of a bay or chestnut 
color. Though much less flat than a flax seed, its resemblance 
in color, size and form, to that familiar object, is so striking as 
at once to be remarked by every one. The figures A, i and j, of 
plate 3 give dorsal, ventral and lateral views of this flax-seed 
state of the insect. 
When the warm days of early spring arrive, and the weather 
becomes sufficiently mild for some of our earliest plants to put 
forth their blossoms, the larva of the Hessian fly is by the genial 
warmth rapidly stimulated to maturity. In the year 1846, most 
of these insects wore found changed from their larva to their pupa 
state, so early as the 21st of April. But as the season then was 
more forward than usual at that date, this was probably earlier 
than the change commonly occurs in the middle and northern 
parts of New York. A more accurate criterion by which to 
indicate the time when this change occurs, no doubt, is the pro¬ 
gress which vegetation has then made. 1 may therefore state 
that, in all parts of our country, the Hessian fly will be found in 
its fully formed pupa state, about a week after the liverwort 
(Hepatica triloba), the trailing arbutus (Epigcea repens), and the 
red or swamp maple (Acer rubrum) first begin to be seen in 
bloom in our woods. The insect remains in this stage of its 
life about ten or twelve days, and then gives out the winged fly. 
When the insect has reached its pupa state, the flax seed shell 
in which it lies inclosed has become quite brittle, breaking 
