﻿HOW 
  INSECTS 
  FLY 
  SNODGRASS 
  

  

  419 
  

  

  before 
  it. 
  The 
  rate 
  of 
  the 
  wing 
  movements 
  then 
  must 
  be 
  just 
  suffi- 
  

   cient 
  to 
  create 
  a 
  balance 
  with 
  the 
  pull 
  of 
  gravity. 
  A 
  drift 
  on 
  air 
  

   currents 
  must 
  be 
  counteracted 
  by 
  compensatory 
  changes 
  in 
  the 
  angle 
  

   of 
  the 
  wing 
  vibrations. 
  

  

  An 
  interesting 
  illustration 
  showing 
  the 
  course 
  taken 
  by 
  a 
  honeybee 
  

   or 
  by 
  a 
  drone 
  fly 
  approaching 
  a 
  group 
  of 
  flowers 
  is 
  given 
  by 
  Stell- 
  

   waag. 
  (Fig. 
  25.) 
  The 
  insect 
  arrives 
  head 
  on, 
  arrests 
  its 
  flight 
  and 
  

   swings 
  to 
  the 
  right 
  or 
  left 
  still 
  headed 
  toward 
  the 
  flowers; 
  next, 
  it 
  

   circles 
  about 
  in 
  ordinary 
  forward 
  flight, 
  making 
  a 
  closer 
  approach; 
  

   now, 
  perhaps, 
  it 
  hovers, 
  agam 
  zigzags 
  sideways, 
  and 
  finally 
  goes 
  direct 
  

   to 
  a 
  particular 
  blossom. 
  

  

  Considering 
  how 
  adept 
  are 
  insects 
  on 
  the 
  wing, 
  it 
  seems 
  certain 
  that 
  

   they 
  must 
  have 
  a 
  highly 
  developed 
  "sense" 
  of 
  equilibrium. 
  And 
  yet, 
  

   among 
  the 
  numerous 
  and 
  diverse 
  sense 
  organs 
  with 
  which 
  insects 
  are 
  

   known 
  to 
  be 
  equipped, 
  organs 
  to 
  v/hich 
  might 
  be 
  assigned 
  a 
  static 
  

   function, 
  or 
  the 
  control 
  of 
  balance, 
  have 
  been 
  found 
  in 
  very 
  few 
  cases, 
  

   and 
  principally 
  in 
  

   certain 
  small 
  forms 
  

   (Phylloxera) 
  with 
  

   limited 
  powers 
  of 
  

   flight. 
  Lacking 
  evi- 
  

   dence 
  of 
  the 
  exist- 
  

   ence 
  of 
  organs 
  of 
  

   equilibrium 
  gen- 
  

   erally 
  distributed 
  

   in 
  insects, 
  we 
  might 
  

   suppose 
  that 
  the 
  

   maintenance 
  of 
  bal- 
  

   ance 
  during 
  flight 
  is 
  

   an 
  automatic 
  reac- 
  

   tion 
  through 
  the 
  

   sense 
  of 
  sight. 
  The 
  writer 
  has 
  found, 
  however, 
  that 
  a 
  large 
  swallowtail 
  

   butterfly 
  {Papilio 
  polyxenes) 
  is 
  able 
  to 
  fly 
  well 
  after 
  having 
  its 
  eyes 
  

   thoroughly 
  blackened 
  with 
  a 
  mixture 
  of 
  glue 
  and 
  powdered 
  charcoal 
  

   until 
  it 
  no 
  longer 
  reacts 
  to 
  light 
  in 
  a 
  room. 
  (The 
  normal 
  butterfly 
  

   goes 
  at 
  once 
  to 
  a 
  window.) 
  An 
  individual 
  thus 
  blindfolded 
  fluttered 
  

   about 
  aimlessly 
  in 
  a 
  room 
  with 
  three 
  windows 
  on 
  one 
  side, 
  though 
  

   before, 
  when 
  liberated, 
  it 
  flew 
  directly 
  to 
  a 
  window. 
  Taken 
  out 
  of 
  

   doors 
  it 
  immediately 
  flew 
  upward 
  in 
  w^idening 
  circles, 
  finally 
  going 
  

   high 
  over 
  the 
  roof 
  of 
  a 
  two-story 
  house 
  and 
  disappearing 
  over 
  the 
  tops 
  

   of 
  trees 
  beyond. 
  Clearly 
  this 
  insect 
  did 
  not 
  require 
  the 
  use 
  of 
  its 
  

   eyes 
  to 
  keep 
  itself 
  in 
  the 
  proper 
  position 
  for 
  flying. 
  Another 
  individ- 
  

   ual 
  of 
  the 
  same 
  species 
  was 
  able 
  to 
  fly 
  in 
  the 
  normal 
  way 
  when 
  its 
  entire 
  

   head 
  was 
  cut 
  off, 
  though, 
  after 
  the 
  manner 
  of 
  insects 
  lacking 
  a 
  brain, 
  

   it 
  had 
  no 
  inclination 
  to 
  do 
  so, 
  except 
  when 
  artificially 
  stimulated. 
  

   When 
  thrown 
  into 
  the 
  air, 
  it 
  fell 
  straight 
  down, 
  but 
  the 
  sudden 
  con- 
  

   82328—30 
  28 
  

  

  Figure 
  25. 
  — 
  The 
  course 
  taken 
  by 
  a 
  honeybee 
  (.A) 
  and 
  a 
  drone 
  fly 
  (B) 
  

   approaching 
  a 
  flower. 
  (From 
  Stellwaag, 
  1916) 
  

  

  