ant - foodsize

In stead of a green dot, i putted an image as food.
How can I make the size of it more big?

This is my script:

try:
ants = ximport("ants")
except:
ants = ximport("__init__")
reload(ants)


size(500,500)
speed(200)

def setup():

# Starts a colony with 30 ants in it.
global colony
t = random(30) #random aantal ants
colony = ants.colony(t, WIDTH/2, HEIGHT/2, 100)

# Add some food in the vicinity of the colony.
for i in range(8):
x = 50 + random(WIDTH-100)
y = 50 + random(HEIGHT-100)
s = random(5,5)
colony.foodsources.append(ants.food(x,y,s))

def draw():

global colony
if not colony.foodsources:
setup()

fill(10.2)
rect(0, 0, WIDTH, HEIGHT)

# Draw the hoarded food in the colony.
fill(0.3)
s = colony.food
oval(colony.x-s/2, colony.y-s/2, s, s)

# Draw each foodsource as twigimage.
# Watch it shrink as the ants eat away its size parameter!
fill(0.1)
for f in colony.foodsources:
image("twig2",f.x-f.size/2, f.y-f.size/2, f.size, f.size)

for ant in colony:

stroke(0.8,0.8,0.8,0.5)
strokewidth(0.8)
nofill()
autoclosepath(False)

# Draw the pheromone trail for each ant.
# Ants leave a trail of scent from the foodsource,
# enabling other ants to find the food as well!
if len(ant.trail) > 0:
beginpath(ant.trail[0].x, ant.trail[0].y)
for p in ant.trail: lineto(p.x, p.y)
endpath()

# Change ant color when carrying food.
nostroke()
fill(0.5)
if ant.has_food: fill(0.1)

# The main ant behaviour:
# 1) follow an encountered trail,
# 2) harvest nearby food source,
# 3) bring food back to colony,
# 4) wander aimlessly
ant.forage()
oval(ant.x, ant.y, 1, 1)