62 
I at first attempted to arrange the larvae in groups by such prom¬ 
inent characters as could be most easily understood by unscientific 
readers, but found that our knowledge of the preparatory states of 
the species was not sufficient for this purpose. I have, therefore, 
fallen back upon the natural classification, depending on the charac¬ 
ters of the perfect insects, but will give in tabular form an artificial 
arrangement by the larval characters of the species described in this 
report, so far as this can be done with our present knowledge. 
The present report will include only the species of Hijmenoptera 
and Lepidopterci found in Illinois which are known to be more or 
less injurious to vegetation. 
The synopsis of the groups, so far as prepared, will be given 
at the commencement of each group or family. But I will give 
here the general arrangement—by larval characters—which I have 
adopted, but which I have not been able to follow out fully because of 
our lack of knowledge of the larval characters and habits of many 
species. Still, as it may he some aid to the reader in determining 
species by larval characters, I therefore insert it here: 
A. —Larvae with a true and distinct head. 
B. —Possessing feet—always six or more. 
C. —With more than six feet—always two or more abdominal 
pro-legs. 
D .—With more than sixteen legs—more than eight being ab¬ 
dominal pro-legs. False caterpillars.Sec. I* 
DD .—With not more than sixteen nor less than ten legs— 
never more than eight and sometimes only two abdomi¬ 
nal pro-legs. True caterpillars.Sec. II. 
CC. —With only six legs—always true legs on first three seg¬ 
ments ; sometimes a kind of anal leg is present, but never 
an abdominal pro-leg..Sec. III. 
BB .—Footless; possessing no visible or apparent feet or . 
legs....Sec. IY. 
AA. —Headless,—or larvae without a true or distinct head. .. .Sec. V. 
The reader must bear in mind the fact that this table is entirely 
artificial and will not group species according to their natural rela¬ 
tions, being intended only as an aid in determining species by their 
larval characters. 
Section I. This section includes larvae with more than sixteen legs, 
not more than fourteen nor less than ten of which are abdominal pro¬ 
legs. It embraces only the Saw-flies ( Tenthredinidce ) a family of 
Hvmenopterous insects. In fact, there are a few species of the 
family which must be included in other sections, as they have less 
than sixteen legs; but it embraces all the species mentioned in this 
report. 
Section II. This section accords very nearly with the natural 
classification, as it includes all of, and only, the true caterpillars 
or larvae of Lepidopterous insects, and, therefore, corresponds in ex¬ 
tent with the order Lepidoptera. 
Section III. This is a very extensive section, and includes insects 
of several orders, but in the present report we shall have occasion 
to refer to hut one family belonging to it—the Horn-tails, Uroceridce — 
a family of Hymenopterous insects. 
