349 
No. 150.] 
this species, have enabled me fully to trace out this point in its 
transformations, and to show that it is not till near the close of its 
flax seed period of existence that the Hessian fly puts on its pupa 
form. In penning the note just alluded to, I had overlooked a pas¬ 
sage in Mr. Herrick’s last paper, from which it is obvious that he 
has seen the real pupa of the Hessian fly, although he still speaks 
of its pupa stale as commencing when the worm becomes a flax-seed. 
Inaccuracies of this kind, which to the general reader appear so tri¬ 
vial as scarcely to require correcting, are liable to lead to important 
errors. Of this, we have a striking illustration in this very instance. 
Mr. Westwood, on opening the flax seeds contained in the wheat 
straw from Germany, came upon the larva,” where, according to 
all the accounts of the Hessian fly he ought to have found the pupa; 
he therefore at once draws the important inference, that the Ger¬ 
man insect cannot be the Hessian fly of America. Indeed it is sur¬ 
prising, that so plain a fact as this, that it is a worm and not a pupa 
which is enveloped in the flax seed case of our insect, has been so 
wholly overlooked by every one who has hitherto written upon this 
subject. 
The Pupa. When formed. —On the access of the first warm days 
of spring, as soon as the weather becomes sufficiently genial for 
some of our earliest plants to put forth their blossoms, the larva of the 
Hessian fly is rapidly stimulated to maturity. The present year, 
so early as the 21st of April, most of the insects were found to have 
taken on their pupa form. As this season was more forward than 
usual, this may prove to be an earlier date than is common for this 
occurrence ; a more accurate criterion by which to indicate it defi¬ 
nitely, is no doubt by a reference to the progress which vegetation 
has made at this time. We may therefore state, that in all parts of 
our country, the Hessian fly will probably be found in its fully form¬ 
ed pupa state, about a week after the liverwort, ( Ilepatica triloba,) 
the trailing arbutus ( Epigcea repens ), and the red or swamp maple 
{Acer rubrum ,) first appear in bloom, and simultaneously with the 
flowering of the dry strawberry {Comaropsis fragarioides), the com¬ 
mon five-finger {Potentilla canadensis) , the hill-side violet ( Viola 
ovata), &c. It continues in this state about ten or twelve days, and 
then sends out the winged fly. 
