﻿446 
  W. 
  F. 
  FISKE. 
  

  

  Nothing 
  but 
  " 
  insularity 
  " 
  could 
  be 
  attributed 
  as 
  the 
  determining 
  factor 
  in 
  the 
  

   case 
  of 
  spider. 
  Its 
  great 
  abundance 
  is 
  partly 
  due 
  to 
  the 
  incredible 
  numbers 
  of 
  

   " 
  lake 
  flies 
  ' 
  : 
  (Chironomus, 
  mainly) 
  which 
  breed 
  in 
  the 
  lake 
  and 
  frequently 
  rise 
  

   from 
  it 
  in 
  such 
  swarms 
  as 
  to 
  appear 
  like 
  the 
  smoke 
  of 
  a 
  large 
  steamer 
  on 
  the 
  horizon. 
  

   Swarms 
  of 
  them 
  that 
  must 
  number 
  thousands 
  of 
  millions 
  gather 
  and 
  sweep 
  on 
  shore, 
  

   where, 
  if 
  there 
  chances 
  to 
  be 
  a 
  generation 
  of 
  newly 
  hatched 
  spiders 
  coming 
  on, 
  they 
  

   provide 
  an 
  abundance 
  of 
  food 
  at 
  a 
  critical 
  time. 
  Possibly 
  there 
  is 
  some 
  correlation 
  

   between 
  the 
  incidence 
  of 
  lake 
  fly 
  and 
  of 
  spider, 
  which 
  works 
  out 
  to 
  the 
  disadvantage 
  

   of 
  Glossina 
  in 
  the 
  end. 
  

  

  There 
  is 
  less 
  mystery 
  in 
  the 
  case 
  of 
  the 
  dragonfly. 
  The 
  particular 
  species 
  before 
  

   mentioned 
  feeds 
  as 
  nymphs 
  in 
  shallow, 
  rush-grown 
  water, 
  more 
  particularly 
  where 
  

   there 
  is 
  sand 
  and 
  pebbly 
  bottom. 
  The 
  existence 
  of 
  such 
  shallows 
  off 
  shore 
  is 
  detri- 
  

   mental 
  to 
  tsetse 
  on 
  shore. 
  

  

  The 
  Bembex 
  breeds 
  in 
  fine, 
  dry 
  sand, 
  of 
  a 
  sort 
  that 
  it 
  can 
  burrow 
  into 
  without 
  

   its 
  galleries 
  collapsing. 
  It 
  is 
  very 
  irregularly 
  distributed, 
  because 
  this 
  type 
  of 
  soil 
  

   is 
  not 
  at 
  all 
  common. 
  The 
  type 
  is 
  mildly 
  detrimental 
  to 
  tsetse 
  where 
  it 
  occurs. 
  

  

  Absence 
  of 
  rock, 
  both 
  on 
  shore 
  and 
  in 
  the 
  shallows 
  off 
  shore, 
  is 
  a 
  more 
  potent 
  

   factor 
  in 
  its 
  inimical 
  effect 
  on 
  tsetse, 
  for 
  Varanus 
  is 
  a 
  rock-dweller 
  on 
  land, 
  and 
  its 
  

   most 
  favoured 
  food 
  is 
  the 
  crabs 
  and 
  molluscs 
  — 
  especially 
  the 
  crabs 
  — 
  which 
  are 
  only 
  

   found 
  in 
  rocky 
  shallows. 
  There 
  are 
  long 
  reaches 
  of 
  sandy 
  shore 
  south 
  of 
  Dumo 
  

   village, 
  in 
  Buddu, 
  which 
  are 
  virtually 
  free 
  from 
  fly 
  because 
  of 
  absence 
  of 
  food 
  ; 
  only 
  

   crocodile 
  occurs, 
  and 
  only 
  at 
  a 
  few 
  points 
  where 
  buck 
  comes 
  down 
  to 
  the 
  water 
  are 
  

   flies 
  and 
  crocodiles 
  likely 
  to 
  meet. 
  

  

  No 
  trace 
  of 
  Varanus 
  was 
  seen 
  along 
  these 
  reaches. 
  Had 
  it 
  occurred 
  (i.e., 
  if 
  there 
  

   had 
  been 
  food 
  for 
  it, 
  and 
  a 
  rock-bound 
  bottom), 
  its 
  inland 
  wanderings 
  across 
  the 
  

   natural 
  clearing 
  that 
  bordered 
  the 
  shore 
  would 
  have 
  brought 
  it 
  into 
  contact 
  with 
  

   shelter 
  and 
  breeding 
  places, 
  and 
  conditions 
  of 
  life 
  would 
  have 
  been 
  excellent 
  for 
  tsetse. 
  

  

  IX 
  (/). 
  Leopard 
  as 
  a 
  Deprivative 
  Enemy 
  of 
  Glossina 
  palpalis. 
  

  

  Through 
  a 
  combination 
  of 
  partly 
  fortuitous 
  circumstances 
  it 
  is 
  possible 
  to 
  measure 
  

   or 
  estimate, 
  roughly, 
  the 
  effect 
  of 
  the 
  presence 
  and 
  activities 
  of 
  leopards 
  in 
  restricting 
  

   the 
  range 
  and 
  density 
  of 
  Glossina 
  palpalis. 
  It 
  is 
  plainly 
  a 
  more 
  efficacious 
  deprivative 
  

   enemy 
  than 
  spider 
  is 
  a 
  destructive 
  enemy 
  of 
  the 
  insect. 
  The 
  data 
  follow, 
  item 
  

   by 
  item. 
  

  

  (1). 
  On 
  the 
  Sesse 
  Islands 
  there 
  are 
  no 
  leopards 
  or 
  other 
  large 
  beasts 
  of 
  prey. 
  

   Following 
  elimination 
  of 
  the 
  human 
  factor 
  situtunga 
  increased 
  at 
  a 
  rapid 
  rate 
  on 
  

   every 
  island 
  where 
  it 
  occurred, 
  and 
  spread 
  from 
  the 
  marshes 
  to 
  the 
  hills 
  and 
  

   abandoned 
  plantations. 
  As 
  a 
  result 
  the 
  range 
  of 
  fly 
  inland 
  increased 
  from 
  a 
  low 
  

   average 
  of 
  perhaps 
  300 
  yards 
  — 
  not 
  counting 
  stragglers 
  — 
  to 
  one 
  that 
  is 
  at 
  least 
  5 
  times 
  

   greater 
  wherever 
  shelter 
  is 
  good 
  and 
  continuous 
  for 
  this 
  distance 
  inland. 
  

  

  (2). 
  On 
  the 
  two 
  sudd-bound 
  islands 
  of 
  Bunjako 
  and 
  Binga 
  leopard 
  occurred, 
  

   and 
  also 
  situtunga. 
  There 
  was 
  no 
  increase 
  of 
  the 
  latter, 
  nor 
  could 
  evidence 
  be 
  found 
  

   on 
  Bunjako, 
  which 
  is 
  densely 
  fly-infested 
  along 
  its 
  shore, 
  of 
  more 
  than 
  ordinary 
  

   extension 
  of 
  infestation 
  inland. 
  

  

  