﻿HOW 
  INSECTS 
  FLY 
  

  

  By 
  R. 
  E. 
  Snodqrass 
  

   Bureau 
  of 
  Entomology, 
  United 
  States 
  Department 
  of 
  Agriculture 
  

  

  A 
  particular 
  interest 
  attaches 
  to 
  the 
  study 
  of 
  the 
  wings 
  of 
  insects, 
  

   because, 
  in 
  some 
  respects, 
  they 
  act 
  more 
  after 
  the 
  manner 
  of 
  human 
  

   inventions 
  for 
  aerial 
  locomotion 
  than 
  do 
  the 
  wings 
  of 
  any 
  other 
  flying 
  

   creature. 
  Though 
  man 
  has 
  never 
  been 
  successful 
  in 
  equipping 
  him- 
  

   self 
  with 
  wings, 
  and 
  has 
  largely 
  given 
  up 
  the 
  hope 
  of 
  acquiring 
  them, 
  

   he 
  has 
  succeeded 
  in 
  making 
  machines 
  that 
  will 
  fly; 
  and, 
  whether 
  his 
  

   craft 
  is 
  lighter 
  than 
  air 
  or 
  heavier 
  than 
  air, 
  its 
  driving 
  mechanism 
  is 
  

   a 
  set 
  of 
  rotating 
  blades, 
  the 
  nearest 
  counterparts 
  of 
  which 
  in 
  the 
  

   animal 
  world 
  are 
  the 
  rapidly 
  whirring 
  wings 
  of 
  certain 
  insects. 
  

  

  It 
  is 
  impossible, 
  however, 
  to 
  draw 
  any 
  close 
  comparison 
  between 
  

   the 
  structure 
  of 
  man-made 
  machines 
  and 
  that 
  of 
  animal 
  mechanisms. 
  

   There 
  are 
  fundamental 
  principles 
  of 
  physics, 
  or 
  of 
  mechanics, 
  or, 
  

   rather 
  there 
  are 
  fundamental 
  truths 
  of 
  nature, 
  which 
  physicists 
  have 
  

   discovered 
  and 
  mechanics 
  make 
  use 
  of, 
  that 
  give 
  the 
  possibility 
  of 
  

   locomotion 
  both 
  to 
  animals 
  and 
  to 
  machines; 
  but 
  the 
  means 
  by 
  

   which 
  these 
  principles 
  have 
  been 
  employed 
  may 
  differ 
  widely. 
  Man's 
  

   chief 
  idea 
  for 
  producing 
  motion, 
  by 
  other 
  means 
  than 
  his 
  own 
  or 
  

   another 
  creature's 
  muscles, 
  is 
  to 
  make 
  something 
  turn 
  around. 
  The 
  

   windmill, 
  the 
  water 
  wheel, 
  the 
  engine 
  wheel, 
  the 
  propeller, 
  all 
  depend 
  

   for 
  their 
  effect 
  on 
  continuous 
  rotary 
  movement 
  of 
  one 
  part 
  on 
  another. 
  

   The 
  animal, 
  by 
  the 
  very 
  nature 
  of 
  its 
  structure, 
  is 
  debarred 
  from 
  the 
  

   use 
  of 
  separate 
  elements 
  in 
  its 
  motor 
  devices, 
  the 
  parts 
  of 
  its 
  body 
  are 
  

   continuous 
  and 
  can 
  be 
  merely 
  flexible 
  on 
  one 
  another; 
  at 
  best, 
  there- 
  

   fore, 
  they 
  can 
  attain 
  only 
  a 
  partial 
  rotary 
  movement. 
  The 
  source 
  

   of 
  intrinsic 
  movement 
  in 
  animals 
  is 
  always 
  a 
  contractile 
  tissue, 
  in 
  

   most 
  cases 
  a 
  muscle. 
  But 
  a 
  muscle 
  pulls 
  in 
  only 
  one 
  direction; 
  it 
  

   does 
  not 
  expand 
  except 
  as 
  it 
  is 
  opposed 
  by 
  some 
  other 
  force 
  acting 
  in 
  

   the 
  opposite 
  direction. 
  Hence, 
  muscles 
  usually 
  occur 
  in 
  antagonistic 
  

   pairs. 
  In 
  insects, 
  however, 
  the 
  counteraction 
  against 
  muscle 
  contrac- 
  

   tion 
  is 
  often 
  produced 
  by 
  elasticit}'^ 
  in 
  the 
  skeletal 
  element 
  to 
  which 
  

   the 
  muscle 
  is 
  attached. 
  The 
  mechanical 
  principle 
  employed 
  in 
  nearly 
  

   all 
  animal 
  mechanisms, 
  therefore, 
  is 
  that 
  of 
  the 
  lever 
  without 
  other 
  

   elaborations. 
  Hydraulics, 
  however, 
  plays 
  an 
  important 
  part 
  in 
  the 
  

   movements 
  of 
  the 
  alimentary 
  canal, 
  and 
  in 
  the 
  locomotion 
  of 
  soft- 
  

   bodied 
  animals. 
  

  

  382 
  

  

  