﻿CHAPTER 
  V. 
  

  

  INFLUENCE 
  OF 
  METEOROLOGICAL 
  CONDITIONS 
  ON 
  THE 
  

   DEVELOPMENT 
  AND 
  MIGRATIONS 
  OF 
  LOCUSTS. 
  

  

  That 
  the 
  increase 
  and 
  diminution 
  of 
  insects 
  depend 
  very 
  largely 
  upon 
  

   meteorological 
  conditions 
  is 
  now 
  too 
  well 
  known 
  to 
  require 
  further 
  proof- 
  

   As 
  a 
  very 
  general 
  rule, 
  which 
  has 
  but 
  few 
  exceptions, 
  warm, 
  dry 
  years- 
  

   are 
  favorable 
  to 
  an 
  increase 
  of 
  insect 
  life, 
  while 
  cold, 
  wet 
  seasons 
  have 
  

   a 
  tendency 
  to 
  diminish 
  their 
  numbers. 
  Not 
  only 
  is 
  this 
  true, 
  but 
  the 
  

   development 
  is 
  to 
  a 
  large 
  degree 
  in 
  proportion 
  to 
  the 
  heat 
  and 
  dryness 
  ; 
  

   that 
  is 
  to 
  say, 
  when 
  the 
  season 
  is 
  unusually 
  hot 
  and 
  the 
  drought 
  ex- 
  

   cessive, 
  insects 
  abound 
  and 
  enormously 
  exceed 
  their 
  ordinary 
  numbers- 
  

   This 
  is 
  especially 
  noticeable 
  in 
  the 
  case 
  of 
  such 
  insects 
  as 
  the 
  true 
  

   locusts 
  and 
  other 
  Acridians, 
  the 
  chinch-bugs, 
  most 
  of 
  the 
  Aphides 
  and 
  

   many 
  Lepidoptera. 
  But 
  as 
  a 
  general 
  rule 
  the 
  maximum 
  development 
  

   of 
  a 
  species 
  requires 
  two 
  successive 
  favorable 
  years 
  ; 
  at 
  least, 
  such 
  is 
  the 
  

   case 
  with 
  the 
  locusts 
  and 
  chinch-bugs. 
  

  

  We 
  may 
  state, 
  therefore, 
  as 
  a 
  proposition 
  which 
  we 
  presume 
  will 
  be 
  

   admitted 
  as 
  correct, 
  that 
  the 
  development 
  and 
  movements 
  of 
  the 
  locusts 
  are 
  

   very 
  largely 
  influenced 
  by 
  meteorological 
  conditions. 
  The 
  extent 
  to 
  which 
  

   these 
  conditions 
  effect 
  their 
  development 
  and 
  govern 
  their 
  movements- 
  

   is 
  a 
  point 
  not 
  yet 
  fully 
  settled, 
  but 
  much 
  of 
  the 
  uncertainty 
  in 
  this- 
  

   respect 
  has 
  been 
  cleared 
  up 
  by 
  the 
  investigations 
  of 
  the 
  commission. 
  

  

  The 
  effect 
  of 
  wind, 
  heat, 
  cold, 
  and 
  moisture 
  upon 
  the 
  movements 
  of 
  

   the 
  locusts 
  is 
  so 
  marked 
  that 
  it 
  had 
  been 
  observed 
  before 
  the 
  days 
  

   of 
  Pliny 
  ; 
  even 
  the 
  writers 
  of 
  the 
  Old 
  Testament 
  show 
  by 
  their 
  state- 
  

   ments 
  that 
  they 
  were 
  aware 
  that 
  the 
  wind 
  is 
  necessary 
  to 
  aid 
  them 
  in 
  

   flight. 
  Moses 
  states, 
  202 
  "And 
  the 
  Lord 
  brought 
  an 
  east 
  wind 
  upon 
  the 
  

   land 
  all 
  that 
  day, 
  and 
  all 
  that 
  night 
  ; 
  and 
  when 
  it 
  was 
  morning, 
  the 
  east 
  

   wind 
  brought 
  the 
  locusts 
  ; 
  " 
  and 
  again 
  : 
  203 
  "And 
  the 
  Lord 
  turned 
  a 
  mighty 
  

   strong 
  west 
  wind, 
  which 
  took 
  away 
  the 
  locusts, 
  and 
  cast 
  them 
  into 
  the 
  

   Red 
  Sea," 
  

  

  Pliny, 
  as 
  heretofore 
  stated, 
  mentions 
  the 
  fact 
  that 
  certain 
  authors 
  con- 
  

   tend 
  that 
  they 
  coidd 
  not 
  fly 
  at 
  night 
  on 
  account 
  of 
  the 
  cold, 
  although 
  

   he 
  tries 
  to 
  disprove 
  this 
  by 
  the 
  hypothesis 
  that 
  they 
  cross 
  the 
  Mediter- 
  

   ranean 
  Sea 
  from 
  Africa 
  to 
  Italy 
  ; 
  yet 
  it 
  shows 
  that 
  these 
  writers 
  had 
  

   observed 
  the 
  effect 
  of 
  cold 
  upon 
  their 
  flights. 
  

  

  A. 
  Heat 
  and 
  dryness. 
  — 
  As 
  already 
  mentioned 
  in 
  this 
  chapter, 
  migra- 
  

   tory 
  locusts 
  are 
  found 
  only 
  in 
  regions 
  of 
  more 
  than 
  ordinary 
  dryness, 
  

   which 
  are 
  free 
  from 
  the 
  shade 
  and 
  moisture-retaining 
  influence 
  of 
  forests 
  ; 
  

   at 
  least 
  indicating, 
  if 
  not 
  proving, 
  that 
  the 
  migratory 
  instinct 
  is 
  caused 
  

   by, 
  or 
  in 
  some 
  way 
  depends 
  upon, 
  this 
  dry 
  condition 
  of 
  the 
  region 
  in- 
  

   habited. 
  

  

  202 
  Ex., 
  x, 
  13. 
  *» 
  Ex., 
  x, 
  19. 
  

  

  109 
  

  

  