﻿rnOCEEDINGS 
  OF 
  THE 
  FOTTRTH 
  ENTOMOLOGICAL 
  MEETING 
  285 
  

  

  at 
  rest, 
  but 
  the 
  objection 
  is 
  nevertheless 
  only 
  an 
  apparent 
  one, 
  since 
  

   the 
  extreme 
  rapidity 
  of 
  the 
  movements 
  must 
  make 
  the 
  capture 
  of 
  the 
  

   fly 
  a 
  matter 
  of 
  very 
  considerable 
  difficulty 
  for 
  any 
  foe. 
  When 
  the 
  

   insect 
  is 
  on 
  the 
  wing 
  it 
  looks 
  as 
  though 
  it 
  would 
  offer 
  a 
  distinctly 
  easier 
  

   mark 
  than 
  when 
  it 
  is 
  darting 
  back 
  and 
  forth 
  upon 
  a 
  leaf. 
  

  

  These 
  curious 
  habits 
  are 
  not 
  altogether 
  isolated. 
  We 
  find 
  a 
  type 
  

   of 
  motion 
  among 
  Phoridce 
  not 
  dissimilar 
  from 
  that 
  of 
  PlaUj^pezidce, 
  though 
  

   less 
  definite. 
  Among 
  Tipulids, 
  Dicranomyia 
  saltans, 
  Dol., 
  common 
  

   at 
  Calcutta 
  and 
  recognisable 
  by 
  its 
  snow-white 
  tarsi, 
  waves 
  its 
  body 
  

   gently 
  up 
  and 
  down 
  as 
  though 
  it 
  were 
  being 
  swayed 
  by 
  a 
  current 
  of 
  

   air. 
  A 
  gentle 
  up-and-down 
  motion 
  in 
  walking, 
  a 
  sort 
  of 
  " 
  rolling 
  " 
  

   gait, 
  is 
  very 
  often 
  seen 
  in 
  predaceous 
  Rhynchota 
  and 
  Orthoptera, 
  parti- 
  

   cularly 
  in 
  the 
  slender-legged 
  Emesidse 
  and 
  in 
  the 
  Mantidae. 
  The 
  move- 
  

   ments 
  are 
  generally 
  slow 
  and 
  smooth, 
  not 
  jerky 
  or 
  abrupt, 
  and 
  the 
  

   effect 
  of 
  them 
  is 
  very 
  un-insectlike. 
  It 
  is 
  probable 
  that 
  the 
  impression 
  

   of 
  inanimateness, 
  which 
  this 
  sort 
  of 
  motion 
  certainly 
  gives 
  us, 
  is 
  also 
  

   of 
  value 
  to 
  the 
  insect 
  in 
  enabling 
  it 
  to 
  approach 
  its 
  prey. 
  In 
  the 
  case 
  

   of 
  Emesidse 
  the 
  likeness 
  of 
  some 
  species 
  of 
  these 
  predaceous 
  Rhynchota 
  

   to 
  small 
  Tipulidge 
  is 
  very 
  distinct, 
  particularly 
  in 
  the 
  field, 
  and 
  it 
  is 
  

   interesting 
  to 
  find 
  tendencies 
  to 
  a 
  similar 
  type 
  of 
  motion 
  in 
  both 
  groups. 
  

   The 
  case 
  might 
  possibly 
  be 
  regarded 
  as 
  one 
  of 
  convergence, 
  but 
  certainly 
  

   not 
  of 
  mimicry, 
  unless 
  we 
  are 
  prepared 
  to 
  assume 
  that 
  the 
  insects 
  preyed 
  

   upon 
  by 
  Emesidae 
  mistake 
  them 
  for 
  the 
  Tipulidfe 
  which 
  they 
  know 
  to 
  

   be 
  harmless. 
  Emesids 
  are 
  considerably 
  less 
  abundant 
  than 
  Tipulids. 
  

  

  The 
  device 
  of 
  securing 
  a 
  degree 
  of 
  invisibility 
  by 
  means 
  of 
  rapid 
  

   motion 
  is 
  familiar 
  in 
  those 
  spiders 
  which 
  when 
  alarmed 
  cause 
  their 
  

   webs 
  and 
  bodies 
  to 
  quiver 
  so 
  rapidly 
  that 
  we 
  only 
  perceive 
  the 
  insect 
  

   as 
  a 
  sort 
  of 
  blurred 
  spot 
  in 
  the 
  middle 
  of 
  the 
  web. 
  I 
  cannot 
  recall 
  any 
  

   other 
  example 
  of 
  this 
  vibratory 
  type 
  of 
  movement 
  being 
  described 
  as 
  

   a 
  defensive 
  measure, 
  and 
  it 
  may 
  therefore 
  be 
  of 
  interest 
  to 
  mention 
  

   the 
  case 
  of 
  two 
  Tipulidse 
  which 
  I 
  noticed 
  in 
  July 
  of 
  this 
  year 
  (1913). 
  

   These 
  show 
  two 
  varieties 
  of 
  movement 
  which 
  are 
  in 
  my 
  opinion 
  to 
  be 
  

   interpreted 
  as 
  defensive. 
  As 
  in 
  the 
  case 
  of 
  the 
  Platypezid, 
  these 
  move- 
  

   ments 
  were 
  exhibited 
  apparently 
  in 
  response 
  to 
  the 
  movement 
  of 
  com- 
  

   paratively 
  large 
  objects 
  in 
  the 
  insect's 
  vicinity, 
  but 
  no 
  definite 
  measure- 
  

   ments 
  were 
  made. 
  I 
  simply 
  noted 
  that 
  when 
  I 
  remained 
  motionless 
  

   at 
  some 
  little 
  distance, 
  the 
  insects 
  sat 
  still, 
  whereas 
  when 
  I 
  got 
  near 
  

   them 
  or 
  after 
  approaching 
  with 
  caution, 
  waved 
  my 
  hand 
  a 
  foot 
  or 
  two 
  

   away 
  from 
  them, 
  they 
  began 
  their 
  movements, 
  generally 
  quieting 
  down 
  

   again 
  within 
  two 
  or 
  three 
  minutes 
  after 
  I 
  had 
  again 
  retired 
  to 
  a 
  little 
  

   distance. 
  The 
  movements 
  differed 
  curiously 
  in 
  the 
  two 
  species. 
  In 
  

   the 
  first 
  one 
  observed 
  (both 
  were 
  sitting 
  on 
  a 
  tree-trunk), 
  it 
  consisted 
  

  

  