﻿THE 
  SPRING 
  CANKER 
  WORM: 
  DISTRIIBUTION. 
  175 
  

  

  species 
  is 
  tlieelin, 
  and, 
  accordlDg 
  to 
  Mr. 
  JoLn 
  Sears, 
  of 
  Danvers, 
  Mass., 
  

   the 
  black 
  ash 
  [Fraxinus 
  samhucifoUa], 
  both 
  in 
  deep 
  woods 
  and 
  in 
  the 
  

   open 
  meadow, 
  as 
  he 
  has 
  found 
  the 
  females 
  ascending 
  the 
  trees 
  ; 
  but 
  it 
  

   is 
  usually 
  more 
  destructive 
  to 
  the 
  apple, 
  and 
  at 
  times 
  to 
  the 
  cherry. 
  

  

  It 
  is 
  no 
  proof, 
  however, 
  that 
  the 
  black 
  ash 
  is 
  a 
  food-plant, 
  above 
  all 
  

   the 
  native 
  food-plant, 
  that 
  the 
  females 
  ascend 
  the 
  trees, 
  for 
  they 
  will 
  

   ascend 
  sticks, 
  fences, 
  or 
  any 
  other 
  object 
  ui)on 
  which 
  they 
  can 
  climb. 
  

  

  Ai^ple-trees 
  seem 
  to 
  be 
  their 
  principal 
  food-plant; 
  for 
  though, 
  in 
  Mis- 
  

   souri, 
  we 
  have 
  found 
  the 
  worms 
  on 
  plum 
  and 
  elm, 
  we 
  have 
  never 
  known 
  

   them 
  there 
  to 
  do 
  as 
  great 
  injury 
  to 
  these 
  trees 
  as 
  to 
  apple. 
  

  

  MODES 
  OF 
  DISTRIBUTION. 
  

  

  Although 
  the 
  females 
  are 
  wingless, 
  and 
  can, 
  in 
  consequence, 
  only 
  crawl 
  

   from 
  place 
  to 
  place, 
  the 
  insect 
  is 
  able 
  to 
  spread 
  rapidly, 
  in 
  localities 
  

   where 
  it 
  appears 
  in 
  numbers, 
  for 
  the 
  larvae 
  can 
  pass 
  from 
  tree 
  to 
  tree 
  

   without 
  much 
  difficulty. 
  When 
  full 
  grown 
  or 
  nearly 
  so, 
  and 
  dropping 
  

   by 
  their 
  silken 
  threads 
  to 
  the 
  ground, 
  the 
  suspended 
  worms 
  are 
  caught 
  

   up 
  l;)y 
  the 
  winds 
  and 
  wafted 
  to 
  other 
  trees, 
  many 
  of 
  them 
  swinging 
  off 
  

   upon 
  their 
  threads 
  to 
  considerable 
  distances. 
  "While 
  hanging 
  from 
  

   limbs 
  above 
  the 
  traveled 
  roads, 
  moreover, 
  they 
  are 
  often 
  swept 
  off 
  by 
  

   passing 
  carriages, 
  and 
  are 
  thus 
  conveyed 
  to 
  other 
  places. 
  

  

  Le 
  Baron 
  says, 
  in 
  his 
  second 
  Illinois 
  report 
  (p. 
  108) 
  : 
  

  

  I 
  saw 
  some 
  to-day 
  [May 
  24, 
  1871] 
  floating 
  30 
  feet 
  from 
  the 
  tree. 
  As 
  the 
  web 
  by 
  

   which 
  they 
  are 
  suspended 
  is 
  scarcely 
  visible, 
  the 
  worms 
  often 
  have 
  the 
  appearance 
  

   of 
  flying 
  in 
  the 
  air. 
  At 
  the 
  same 
  time 
  I 
  could 
  find 
  very 
  few 
  worms 
  on 
  the 
  trunk, 
  

   showing 
  that 
  their 
  normal 
  way 
  of 
  migrating 
  is 
  not 
  by 
  crawling 
  down 
  the 
  tree, 
  but 
  

   by 
  floating 
  off 
  on 
  threads. 
  

  

  The 
  observations 
  of 
  Mr. 
  Howell 
  only 
  confirm 
  the 
  previous 
  statements 
  

   as 
  to 
  the 
  manner 
  in 
  which 
  these 
  pests 
  are 
  diffused 
  over 
  large 
  tracts 
  of 
  

   country, 
  particularly 
  in 
  the 
  West, 
  when 
  high 
  winds 
  prevail. 
  He 
  says 
  : 
  

  

  Caught 
  up 
  by 
  the 
  gales 
  while 
  suspended 
  upon 
  their 
  gossamer 
  web, 
  I 
  have 
  seen 
  mul- 
  

   titudes 
  carried 
  far 
  away, 
  flying, 
  thus 
  supported, 
  for 
  long 
  distances. 
  

  

  ENEMIES. 
  

  

  Like 
  most 
  of 
  our 
  noxious 
  insects. 
  Canker 
  Worms 
  are 
  subject 
  to 
  the 
  

   attacks 
  of 
  cannibal 
  and 
  parasitic 
  insects. 
  They 
  are 
  also 
  devoured 
  by 
  

   very 
  many 
  different 
  birds, 
  some 
  of 
  which 
  for 
  a 
  time 
  subsist 
  almost 
  wholly 
  

   upon 
  these 
  pests. 
  Hogs 
  are 
  very 
  efficient 
  in 
  rooting 
  up 
  and 
  devouring 
  

   the 
  chrysalids 
  during 
  the 
  summer 
  months. 
  

  

  Notlirus 
  ovivoruSj 
  Pack. 
  (Fig. 
  2), 
  devours 
  the 
  eggs, 
  probably 
  of 
  the 
  

   Fall 
  species. 
  

  

  The 
  most 
  common 
  parasite 
  which 
  we 
  found 
  in 
  Missouri 
  infesting 
  the 
  

   larva 
  of 
  the 
  Spring 
  Canker 
  Worm 
  is 
  a 
  small, 
  four-winged 
  fly 
  (Micro- 
  

   gaster 
  paleacritce 
  Eiley).^^ 
  After 
  issuing 
  from 
  its 
  victim 
  the 
  Microgaster 
  

   larva 
  spins 
  its 
  pale, 
  greenish-white 
  cocoon 
  alone, 
  and 
  not 
  in 
  company. 
  

  

  «> 
  Notes 
  on 
  N. 
  A. 
  Microgastera. 
  Trans. 
  Acad. 
  Sci., 
  Saint 
  Louis, 
  vol. 
  4, 
  p. 
  311. 
  

  

  