﻿70 
  REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  Cossacks 
  and 
  Tartars. 
  It 
  is 
  therefore 
  essentially 
  different 
  from 
  the 
  dis- 
  

   tricts 
  of 
  the 
  two 
  migratory 
  Calopteni, 
  agreeing 
  with 
  them 
  only 
  in 
  want 
  

   of 
  arboreal 
  vegetation 
  and 
  dryness. 
  

  

  The 
  region 
  which 
  forms 
  the 
  home 
  of 
  A. 
  peregrinum 
  is 
  essentially 
  dif- 
  

   ferent 
  from 
  either 
  of 
  the 
  others. 
  It 
  is 
  composed 
  of 
  the 
  arid 
  and 
  desert 
  

   plains 
  of 
  Northern 
  Africa 
  and 
  Arabia, 
  where 
  rain 
  but 
  seldom 
  falls 
  and 
  

   tropical 
  heat 
  reaches 
  its 
  maximum. 
  Although 
  the 
  term 
  desert 
  has 
  been 
  

   applied 
  to 
  this 
  region, 
  the 
  fact 
  must 
  be 
  borne 
  in 
  mind, 
  as 
  stated 
  by 
  

   Humboldt, 
  that 
  extensive 
  areas 
  in 
  the 
  midst 
  of 
  these 
  deserts 
  are 
  covered 
  

   with 
  at 
  least 
  a 
  scanty 
  vegetation, 
  often 
  sufficient 
  for 
  limited 
  pasturage. 
  

  

  It 
  is 
  therefore 
  apparent 
  that 
  locusts 
  avoid 
  the 
  heavily 
  forest-clad 
  areas 
  

   and 
  select 
  the 
  open 
  regions 
  as 
  their 
  abode. 
  It 
  is 
  also 
  evident 
  that 
  they 
  

   seek 
  the 
  drier 
  areas, 
  avoiding 
  the 
  moist 
  sections, 
  where 
  the 
  rain 
  precipi- 
  

   tation 
  is 
  abundant. 
  Some, 
  as 
  A. 
  peregrinum 
  and 
  A. 
  americanum* 
  require 
  

   also 
  the 
  fervent 
  heat 
  of 
  the 
  tropics 
  to 
  develop 
  them 
  in 
  migratory 
  swarms, 
  

   whilst 
  others, 
  as 
  C. 
  spretus, 
  although 
  delighting 
  in 
  the 
  warm 
  sunshine 
  of 
  

   summer 
  days, 
  will, 
  if 
  the 
  atmosphere 
  be 
  dry, 
  nourish 
  in 
  a 
  moderate 
  de- 
  

   gree 
  of 
  cold. 
  

  

  As 
  heretofore 
  stated, 
  it 
  is 
  much 
  more 
  difficult 
  to 
  draw 
  the 
  line 
  of 
  the 
  per- 
  

   manent 
  distribution 
  of 
  C. 
  spretus 
  than 
  that 
  which 
  marks 
  the 
  limits 
  of 
  its 
  

   migrations. 
  That 
  the 
  former 
  falls 
  without 
  (east 
  of) 
  the 
  mountain 
  range 
  

   as 
  far 
  south 
  as 
  Denver, 
  we 
  may 
  assume 
  pretty 
  well 
  settled 
  by 
  the 
  obser- 
  

   vations 
  of 
  the 
  commissioners 
  in 
  person, 
  each 
  having 
  gone 
  over 
  this 
  

   ground 
  in 
  a 
  different 
  season 
  from 
  the 
  others. 
  That 
  it 
  bends 
  westward 
  

   and 
  enters 
  the 
  mountains 
  a 
  short 
  distance 
  south 
  of 
  this 
  point, 
  we 
  think 
  

   may 
  be 
  safely 
  assumed 
  from 
  the 
  evidence 
  we 
  have 
  obtained. 
  Proceed- 
  

   ing 
  northward 
  from 
  Denver, 
  it 
  bends 
  eastward 
  as 
  we 
  advance, 
  embracing: 
  

   the 
  western 
  portion 
  of 
  Nebraska 
  and 
  a 
  large 
  part 
  of 
  Dakota, 
  and 
  extend- 
  

   ing 
  northward 
  from 
  thence 
  into 
  British 
  America, 
  following 
  approximately 
  

   the 
  103° 
  meridian 
  until 
  it 
  reaches 
  the 
  southern 
  limit 
  of 
  the 
  forests, 
  about 
  

   the 
  53d 
  parallel 
  of 
  latitude. 
  Thence 
  it 
  bends 
  westward, 
  as 
  given 
  in 
  map- 
  

   No. 
  1. 
  The 
  portion 
  of 
  the 
  plains 
  east 
  of 
  the 
  mountains 
  which 
  should 
  be 
  

   included 
  in 
  this 
  area 
  is 
  a 
  matter 
  of 
  considerable 
  uncertainty, 
  nor 
  is 
  the 
  

   line 
  one 
  that 
  can 
  be 
  rigidly 
  marked. 
  

  

  The 
  north 
  and 
  northwest 
  boundary 
  appears 
  to 
  be 
  somewhat 
  strictly 
  

   limited 
  by 
  the 
  forest 
  line, 
  though 
  our 
  data 
  in 
  reference 
  to 
  the 
  regions, 
  

   beyond 
  this 
  line 
  cannot 
  be 
  considered 
  as 
  conclusive. 
  

  

  The 
  western 
  boundary 
  is 
  yet 
  a 
  matter 
  of 
  uncertainty, 
  but 
  it 
  is 
  quite 
  

   probable, 
  from 
  all 
  the 
  facts 
  we 
  have 
  been 
  able 
  to 
  gather, 
  that 
  most 
  of 
  

   Idaho, 
  Wyoming, 
  and 
  the 
  northern 
  half 
  of 
  Utah 
  will 
  have 
  to 
  be 
  included,, 
  

   if 
  we 
  define 
  the 
  breeding- 
  grounds 
  in 
  the 
  sense 
  heretofore 
  explained. 
  

  

  This 
  region 
  may 
  be 
  briefly 
  characterized 
  as 
  follows 
  : 
  Starting 
  at 
  the 
  

   point 
  where 
  the 
  southern 
  boundary 
  of 
  Colorado 
  crosses 
  the 
  105th 
  me- 
  

   ridian, 
  the 
  main 
  or 
  eastern 
  range 
  of 
  the 
  Rocky 
  Mountains 
  runs 
  almost 
  

  

  * 
  Note.— 
  Although 
  I 
  have 
  throughout 
  spoken 
  of 
  A. 
  americanum 
  as 
  migratory 
  in 
  Central 
  America, 
  I< 
  

   "Would 
  not 
  he 
  surprised 
  if 
  the 
  species 
  found 
  migratory 
  there 
  should 
  prove 
  to 
  he 
  distinct. 
  

  

  