natsel

breed [predators predator]
breed [bugs bug]
bugs-own [bigness]

to setup
  ca
  create-bugs 30
  ask bugs [setxy random-xcor random-ycor
    set heading 0
    set color white
    set size 1
    set shape Type-of-organism]
ask n-of 5 bugs with [color = white] [set color red]
ask n-of 5 bugs with [color = white][set color blue]
ask n-of 5 bugs with [color = white] [set color green]
ask n-of 5 bugs with [color = white] [set color violet]
ask n-of 5 bugs with [color = white] [set color yellow]
ask n-of 5 bugs with [color = white] [set color brown]
 set-size
   
  create-predators 1 [
    set shape "bird"
    set color yellow
    set size 3
    set heading 315  ]
  reset-ticks
end 

to set-size
  ask bugs [set bigness random 10]
  ask bugs [set size bigness] 
end 

to reproduce
  ask bugs [
    if random 100 > 25 [
      hatch 1 [setxy random-xcor random-ycor
        set heading 0
        ifelse random 10 > 5 
        [set size size + .5 ]
        [set size size - .5]]]]
end 

to move-predator
  ask predators [
    setxy mouse-xcor mouse-ycor
    set hidden? not mouse-inside?
  ]
end 

to go
tick 
  check-caught
  move-predator
  ask bugs [if size <= .05[die]]
  if count bugs < 10 [user-message (word "There are " count bugs " bugs. Hit Halt and Reproduce before continuing")]
end   

to check-caught
  if not mouse-down? or not mouse-inside? [ stop ]
  let prey [bugs in-radius (size / 3 )] of one-of predators
  ;; no prey here? oh well
  if not any? prey [ stop ]
  ;; eat only one of the bugs at the mouse location
  ask one-of prey [
    die
  ]
end