1894,] Unusual Flights of the Crouse Locust. 483 
UNUSUAL FLIGHTS OF THE GROUSE LOCUST 
(TETTIGIDEA LATERALIS SAY,) IN NORTH 
EASTERN ILLINOIS. 
By Joseru L. Hancock. 
At certain times, seemingly without premonitory indica- 
tions, some insects suddenly change their habitat; although 
closely allied forms inhabiting the same locality under simi- 
lar general influences, show no disposition to do so. That 
there are predisposing conditions which are the ruling causes 
of these specific migrations is plainly evinced by careful 
study. Before confining our remarks to a single species 
Tettigidea lateralis Say, “ The Grouse Locust” as an illustration 
in point, a sketchy recapitulation of the phenomena of migra- 
tion in the family Acrididæ, of which the above is a member, 
may be given to some advantage. The various forms of 
grasshoppers, constituting this large family, are not as a rule 
migratory ; as a matter of fact, somewhere near a dozen only 
are given to making sudden sweeping changes, by flight over 
a large territory foreign to their hatching grounds. In two 
species, whose anatomical differences are but very slight, one 
may be truly migratory while the other is not, as seen for 
example, in Melanoplus spretus and Melanoplus femurrubrum. 
The confusion arising from an indefinite interpretation of 
migration in its truest sense, as distinguished from the shorter 
“local flights” as appled to insects, is often perplexing. Let 
us attempt to set at rest, as far as possible, such misconception 
of terms. 
Individuals of a species which effeet a more or less regular 
periodical change in their habitat, are truly migratory. 
Migrations may be primary, consisting of local flights; such as 
movements by insects hatched in temporary regions to which 
they confine themselves to passing to and fro, from point to 
point, or secondary, asthe repeated periodical changes of resi- 
- dence covering foreign fields, which virtually establishes a 
‘Nomadic habit. We have hinted that there are predetermining 
