Backyard Biology

Nature stories from my backyard and beyond

Nature Activities

Breaking Trail

May 7, 2010

Follow an ant for a while and it might look like the ant is wandering aimlessly. Chances are you are watching a scout ant and she is searching for food. When she leaves the nest, she will wander around in a random path until she finds a food source. After having fed, she heads back to the nest in a more or less straight path to alert her nestmates of this food source. Unlike honeybees who instruct their nestmates where the food source is by a waggle dance, the ants will leave a trail for their sisters to follow.
As the scout returns to the nest, she will lay down a chemical - or pheromone - trail on the ground. Other ants at the nest will follow this trail to the food source. After feeding, they will return to the nest along the trail, adding their own pheromones to the trail. This will keep the trail fresh. Otherwise the pheromones would soon evaporate and the trail will disappear. The ants will continue to add to the trail as long as the food supply lasts. Once the food source is gone, the ants no longer resupply the pheromones and the trail soon disappears.

A simple experiment can demonstrate how the ants will follow this trail and can become confused when the trail is interrupted or altered.

Setting up the experiment
Locate an ant nest. It can be an underground nest in a crack in the sidewalk, a mound nest in your back yard or even a nest you have located inside your
house.

bait on bricks image

Place an index card about 5-10 inches away from the nest. Secure the card to the substrate – either taping it onto the sidewalk or staking it to the ground using toothpicks.

Place a little food in the center of the card. You can experiment with different foods, either trying them one at a time or putting a number of different foods on the card to see which the ants prefer. Some good choices are peanut butter and honey.

Wait for a scout ant to find and fill up on the food.ant eating honey image

Now watch to see if the ant makes a “beeline” back to the nest. If you have a magnifying glass, you might watch the ant closely to see if you can see it’s rear end dragging along the ground, releasing the pheromone to make the trail.

Next you should see ants emerging from the nest and follow the trail back to the food source.

bait on card imageLet a number of ants follow the trail, each adding their pheromone to the trail until it is well established.

 

 

 

Experiments

  1. Run your finger across the trail, wiping away the pheromones and breaking the trail. What effect does that have on the ants. How do the ants find the trail again?
  2. As an ant is on the card eating the food, rotate the card 90 and see which direction the ant takes back to the nest. Does she follow the trail or head back in the correct direction?