﻿I 
  

  

  642 
  EEPORT 
  UNITED 
  STATES 
  GEOLOGICAL 
  SURVEY. 
  

  

  the 
  exceptional 
  years 
  when 
  the 
  locust 
  migrates 
  are 
  periods 
  of 
  unusnal 
  

   heat 
  and 
  dryness, 
  conditions 
  uuusnally 
  favorable 
  tof 
  the 
  excessive 
  in- 
  

   crease 
  of 
  insect 
  life. 
  As 
  may 
  be 
  seen 
  in 
  the 
  accounts 
  of 
  the 
  eastern 
  

   locust, 
  the 
  grass 
  army-svorm, 
  the 
  grain-aphis, 
  the 
  chinch-bag, 
  and 
  other 
  

   less 
  destructive 
  insects, 
  when 
  the 
  early 
  part 
  of 
  the 
  season, 
  the 
  spring 
  

   and 
  early 
  weeks 
  of 
  summer, 
  are 
  warm 
  and 
  dry, 
  without 
  sudden 
  changes 
  

   of 
  temperature, 
  insects 
  abound 
  and 
  enormously 
  exceed 
  their 
  ordinary 
  

   numbers. 
  When 
  two 
  such 
  seasons 
  occur, 
  one 
  after 
  the 
  other, 
  the 
  con- 
  

   ditions 
  become 
  still 
  more 
  favorable 
  for 
  the 
  undue 
  development 
  of 
  in- 
  

   sect 
  life. 
  Now 
  it 
  is 
  well 
  known 
  that 
  in 
  the 
  Eastern 
  States 
  the 
  summers 
  

   of 
  1800 
  and 
  1874, 
  preceding 
  the 
  appearance 
  of 
  the 
  army- 
  worm 
  and 
  

   grain-aphis, 
  were 
  unusually 
  warm 
  and 
  dry, 
  and 
  favorable 
  not 
  only 
  for 
  

   the 
  hatching 
  of 
  the 
  eggs 
  laid 
  the 
  year 
  previous, 
  but 
  for 
  the 
  growth 
  and 
  

   development 
  of 
  the 
  larvae 
  or 
  young. 
  Look 
  now 
  at 
  the 
  conditions 
  for 
  

   the 
  development 
  of 
  locust 
  life 
  on 
  the 
  hot 
  and 
  dry 
  plains, 
  chiefly 
  of 
  Da- 
  

   kota, 
  Montana, 
  Wyoming, 
  and 
  Idaho. 
  We 
  have 
  no 
  extended 
  meteoro- 
  

   logical 
  records 
  from 
  these 
  regions 
  at 
  hand, 
  but 
  it 
  is 
  more 
  than 
  probable 
  

   that 
  the 
  years 
  preceding 
  the 
  migrations 
  of 
  the 
  locusts 
  were 
  exception- 
  

   ally 
  warm 
  and 
  dry, 
  when 
  the 
  soil 
  was 
  parched 
  with 
  long 
  sustained 
  

   droughts, 
  as 
  we 
  know 
  that 
  the 
  corresponding 
  species 
  east 
  of 
  the 
  Missis- 
  

   sippi 
  liiver 
  abounds 
  during 
  dry 
  summers 
  follosving 
  dry 
  and 
  warm 
  springs. 
  

  

  Given, 
  then, 
  the 
  exceptional 
  years 
  of 
  drought 
  and 
  heat 
  and 
  the 
  great 
  

   extent 
  of 
  territory, 
  and 
  we 
  have 
  as 
  the 
  result 
  vast 
  numbers 
  of 
  young 
  

   hatched 
  out. 
  The 
  year 
  previous 
  having 
  perhaps 
  been 
  warm 
  and 
  dry, 
  

   the 
  locusts 
  would 
  abound, 
  and 
  more 
  eggs 
  than 
  usual 
  would 
  be 
  laid. 
  

   These 
  would 
  with 
  remarkably 
  few 
  exceptious 
  hatch, 
  and 
  the 
  young 
  soon 
  

   consume 
  the 
  buifalo 
  grass 
  and 
  other 
  herbage, 
  and 
  move 
  about 
  from 
  one 
  

   region 
  to 
  another, 
  following 
  often 
  a 
  determinate 
  course 
  in 
  search- 
  of 
  

   food. 
  In 
  this 
  way 
  large 
  broods 
  may 
  migrate 
  a 
  long 
  distance, 
  from 
  per- 
  

   haps 
  twenty 
  to 
  fitty 
  miles. 
  In 
  about 
  six 
  or 
  seven 
  weeks 
  they 
  acquire 
  

   wings. 
  Experience 
  shows 
  that 
  the 
  western 
  locust 
  as 
  soon 
  as 
  it 
  is 
  fledged 
  

   rises 
  up 
  high 
  in 
  the 
  air, 
  sometimes 
  a 
  thousand 
  feet 
  or 
  much 
  higher. 
  

   They 
  have 
  been 
  i:-een 
  to 
  settle 
  at 
  night 
  on 
  the 
  ground, 
  eat 
  during 
  this 
  

   time, 
  and 
  toward 
  noon 
  of 
  the 
  next 
  day 
  fill 
  the 
  air 
  again 
  with 
  their 
  

   glistening 
  wings. 
  As 
  more 
  and 
  more 
  become 
  fledged, 
  the 
  vast 
  swarm 
  

   exhausts 
  the 
  supply 
  of 
  food, 
  and 
  when 
  the 
  hosts 
  are 
  finally 
  marshaled, 
  

   new 
  swarms 
  joining 
  perhaps 
  the 
  original 
  one, 
  the 
  whole 
  swarm, 
  possibly 
  

   hundreds 
  of 
  miles 
  in 
  extent, 
  begins 
  to 
  fly 
  off, 
  borne 
  by 
  the 
  prevailing 
  i 
  

   westerly 
  and 
  northwesterly 
  winds, 
  in 
  a 
  generally 
  easterly 
  and 
  south- 
  : 
  

   easterly 
  course. 
  i 
  

  

  (2.) 
  The 
  secondary 
  cause 
  of 
  the 
  migration 
  is 
  the 
  desire 
  for 
  food, 
  and 
  j 
  

   possibly 
  the 
  reproductive 
  instinct 
  The 
  fact 
  that 
  in 
  their 
  migrations 
  the 
  : 
  

   locusts 
  often 
  seem 
  to 
  select 
  cultivated 
  tracts, 
  rapidly 
  cross 
  the 
  treeless, 
  j 
  

   barren 
  plains, 
  and 
  linger 
  and 
  die 
  on 
  the 
  prairies 
  and 
  western 
  edge 
  of 
  j 
  

   the 
  fertile 
  valleys 
  of 
  the 
  Missouri 
  and 
  Mississippi, 
  indicates 
  that 
  the 
  im- 
  ) 
  

   pelling 
  force 
  is 
  due 
  primarily 
  to 
  the 
  want 
  of 
  food, 
  and 
  that 
  the 
  guiding 
  ) 
  

   force 
  is 
  the 
  direction 
  of 
  the 
  prevailing 
  winds, 
  for 
  they 
  have 
  no 
  leaders, 
  7 
  

   and 
  we 
  do 
  not 
  believe 
  in 
  the 
  existence 
  of 
  a 
  " 
  migratory 
  instiuct" 
  in 
  the 
  

   locust 
  any 
  more 
  than 
  in 
  the 
  grass 
  army-worm, 
  or 
  the 
  cotton 
  army-worm, 
  

   which 
  it' 
  is 
  sufficiently 
  evident 
  migrate 
  from 
  field 
  to 
  field, 
  simply 
  in 
  , 
  

   search 
  of 
  more 
  abundant 
  food.* 
  Meanwhile 
  the 
  reproductive 
  system 
  of 
  

  

  *The 
  siuiplt) 
  fact 
  that 
  tbo 
  more 
  extensive 
  migrations 
  of 
  the 
  locust 
  both 
  in 
  the 
  New 
  

   and 
  Old 
  World 
  are 
  periodical, 
  long 
  intervals 
  existing 
  between 
  them, 
  suggests 
  that 
  the 
  * 
  

   development 
  of 
  a 
  migratory 
  instinct 
  would 
  be 
  impossible. 
  If 
  once 
  partially 
  implanted, 
  1) 
  

   the 
  long 
  succession 
  of 
  non-migratory 
  years 
  would 
  etfectually 
  break 
  up 
  the 
  germs 
  of 
  

   8uch 
  an 
  instinct. 
  It 
  may 
  be 
  quite 
  different 
  with 
  birds, 
  which 
  perlorm 
  their 
  annual 
  

   migrations 
  for 
  years 
  and 
  perhaps 
  centuries 
  without 
  fail. 
  

  

  