﻿376 
  W. 
  F. 
  FISKE. 
  

  

  IV 
  (a). 
  The 
  "Following 
  Swarm" 
  of 
  Glossina 
  palpalis. 
  

  

  Many 
  observations, 
  but 
  few 
  detailed 
  experiments 
  were 
  made 
  upon 
  the 
  curious 
  

   habit 
  of 
  Glossina 
  palpalis 
  of 
  approaching 
  and 
  scrutinising 
  strange 
  objects. 
  It 
  was 
  

   noted 
  that 
  there 
  is 
  ordinarily 
  little 
  discernible 
  difference 
  in 
  this 
  behaviour 
  toward 
  

   inanimate 
  and 
  animate 
  obj 
  ects 
  other 
  than 
  their 
  favoured 
  hosts. 
  When 
  the 
  percentage 
  

   of 
  females 
  amongst 
  active 
  flies 
  is 
  low, 
  man 
  is 
  almost 
  immune 
  to 
  attack, 
  but 
  his 
  person 
  

   is 
  none 
  the 
  less, 
  and 
  equally 
  with 
  any 
  other 
  similarly 
  conspicuous 
  object, 
  strangely 
  

   attractive 
  both 
  to 
  the 
  food-hunting 
  flies 
  of 
  both 
  sexes, 
  and 
  to 
  the 
  relatively 
  inactive 
  

   males. 
  It 
  is 
  on 
  this 
  account 
  that 
  the 
  males 
  are 
  so 
  easily 
  caught, 
  whether 
  or 
  not 
  

   they 
  are 
  seeking 
  food. 
  

  

  Of 
  all 
  objects, 
  apart 
  from 
  their 
  favoured 
  hosts, 
  the 
  most 
  curiously 
  attractive 
  

   to 
  flies 
  is, 
  perhaps, 
  an 
  open 
  dark-coloured 
  umbrella, 
  and 
  in 
  the 
  catching 
  experiments 
  

   and 
  fly 
  survey 
  work 
  the 
  fly 
  boys 
  were 
  each 
  provided 
  with 
  one. 
  When 
  displayed 
  

   at 
  any 
  point 
  in 
  or 
  near 
  the 
  course 
  followed 
  by 
  food-hunting 
  flies, 
  or 
  the 
  relatively 
  

   inactive 
  males, 
  it 
  becomes 
  so 
  conspicuous 
  an 
  object 
  as 
  to 
  attract 
  to 
  it 
  virtually 
  

   all 
  flies 
  which 
  perceive 
  it. 
  They 
  crawl 
  over 
  it, 
  especially 
  its 
  underside, 
  inspecting 
  

   it 
  curiously 
  until 
  curiosity 
  is 
  satiated 
  — 
  or 
  for, 
  perhaps, 
  one 
  to 
  five 
  minutes 
  — 
  -when 
  they 
  

   pass 
  on. 
  And 
  this 
  is 
  equally 
  true 
  of 
  both 
  idle 
  males 
  and 
  food- 
  hunting 
  individuals 
  

   of 
  both 
  sexes. 
  Despite 
  the 
  extraordinary 
  attraction 
  of 
  the 
  obj 
  ect 
  there 
  is 
  no 
  tendency 
  

   on 
  the 
  part 
  of 
  any 
  flies 
  to 
  linger 
  more 
  than 
  the 
  few 
  minutes 
  required 
  for 
  its 
  inspection, 
  

   so 
  that 
  a 
  swarm 
  will 
  never 
  collect. 
  If 
  the 
  density 
  of 
  the 
  stream 
  of 
  passing 
  flies 
  is 
  

   20 
  or 
  30 
  per 
  hour, 
  there 
  will 
  be 
  from 
  one 
  to 
  four 
  or 
  five 
  flies 
  resting 
  on 
  the 
  attractive 
  

   object 
  at 
  all 
  times, 
  but 
  the 
  same 
  flies 
  do 
  not 
  remain 
  for 
  long. 
  

  

  As 
  above 
  stated, 
  the 
  behaviour 
  of 
  the 
  flies 
  toward 
  man 
  is, 
  ordinarily 
  — 
  i.e., 
  when 
  

   the 
  man 
  is 
  alert, 
  food 
  is 
  plentiful 
  and 
  the 
  female 
  percentage 
  low 
  — 
  indistinguishable 
  

   from 
  their 
  behaviour 
  toward 
  his 
  coat 
  thrown 
  over 
  a 
  bush 
  or 
  his 
  umbrella 
  openly 
  

   displayed. 
  It 
  is 
  not 
  necessary 
  to 
  think 
  about 
  the 
  flies 
  or 
  to 
  ward 
  them 
  off: 
  ; 
  

   occasionally 
  one 
  will 
  bite, 
  but 
  the 
  number 
  doing 
  so 
  is 
  so 
  small 
  that 
  it 
  is 
  not 
  worth 
  

   thinking 
  about. 
  Man 
  is 
  attractive 
  to 
  flies, 
  but 
  does 
  not 
  hold 
  them 
  after 
  their 
  curiosity 
  

   is 
  satisfied. 
  The 
  same 
  is 
  true 
  of 
  goats, 
  sheep, 
  and 
  many 
  other 
  animals. 
  

  

  But 
  with 
  certain 
  animals 
  under 
  certain 
  conditions 
  the 
  behaviour 
  of 
  the 
  flies 
  is 
  

   conspicuously 
  different. 
  When 
  a 
  crocodile 
  or 
  Varanus 
  is 
  basking 
  in 
  half 
  open 
  

   sunlight, 
  the 
  flies 
  attracted 
  to 
  them 
  are 
  apt 
  not 
  to 
  pass 
  on, 
  after 
  cursory 
  examination, 
  

   but 
  to 
  linger 
  indefinitely. 
  The 
  result 
  is 
  the 
  gradual 
  accumulation 
  of 
  an 
  accompanying 
  

   or 
  " 
  following 
  " 
  swarm, 
  which 
  may 
  grow 
  to 
  number 
  several 
  times 
  more 
  flies 
  than 
  a 
  

   boy 
  stationed 
  at 
  the 
  same 
  spot 
  would 
  be 
  able 
  to 
  catch 
  in 
  an 
  hour's 
  time, 
  and 
  which 
  

   may 
  certainly 
  represent 
  (sometimes) 
  the 
  accumulation 
  of 
  the 
  majority 
  of 
  flies 
  passing 
  

   the 
  spot 
  during 
  several 
  hours' 
  time. 
  Similar 
  swarms 
  may 
  collect 
  upon 
  or 
  near 
  a 
  

   foraging 
  Varanus, 
  as 
  it 
  wanders 
  slowly 
  through 
  the 
  woodland, 
  or 
  a 
  grazing 
  situtunga, 
  

   and 
  may 
  then 
  follow 
  the 
  animal 
  out 
  of 
  woodland 
  into 
  open 
  grassy 
  spaces, 
  where 
  the 
  

   flies 
  would 
  not 
  go 
  of 
  themselves. 
  

  

  Mention 
  of 
  these 
  conspicuous 
  swarms 
  of 
  flies 
  in 
  connection 
  with 
  Varanus, 
  crocodile, 
  

   tortoise, 
  hippopotamus 
  and 
  situtunga 
  is 
  made 
  in 
  Sect. 
  VI 
  (e). 
  A 
  few 
  additional 
  

   notes 
  excerpted 
  from 
  my 
  field 
  books 
  follow. 
  

  

  