BioEd Online

This experiment examines how ants work together to search a new space. An ant colony must continually monitor its environment to find food, water, and nest sites and to detect threats such as encroachment by ants from another colony. Because ant colonies work without central control, monitoring, foraging, and defense must be done collectively. The colony’s goal is to have ants everywhere, and at all times, so that if something happens, or if food becomes available, a member of the colony will be there to find it and alert the nest. Of course, no colony can do this perfectly. This experiment seeks to answer questions about how colonies adjust their searching strategies in changing conditions.

The investigation examines the search patterns of individual Tetramorium caespitum (pavement) ants at two different population densities, and within the microgravity environment of the ISS and under normal Earth gravity. Pavement ants are common throughout much of the northern and central United States  and also are found in Europe and many other parts of the world.

The following key questions will be investigated:

• When a group of ants is searching a new space, does the shape of an ant’s path depend on the number of ants per unit area?
• Are ants’ searching behaviors and patterns different in a microgravity environment than in Earth’s normal gravity?

Eight habitats, each containing approximately 100 ants, were sent to the ISS on January 7, 2014. The Ants in Space flight habitat is a shallow rectangular box with a clear top through which to view the ants. The box is just a few millimeters deep but provides ample room for ants to move about freely. For ease of handling, the habitats were mounted on plates in sets of four (total of two plates, each with four habitats). Matching habitats containing similar numbers of ants were set up on Earth for observation as controls. During transport to the ISS, the ants were kept in the small “nest” areas of each habitat. The nests contained plaster of paris infused with a nutrient solution to provide food and water.

The ant habitats were loaded and secured on the ISS, and the experiments were conducted on two different days. Each day, four habitats were set up in front of an HD video camera. The astronaut conducting the experiment lowered the barrier on each habitat between the nest area and Forage Area 1 (approximately one-half of the total area of the habitat). This allowed the ants to explore Forage Area 1, and their movements were recorded on video for 25 minutes. After 25 minutes, the astronaut lowered the barrier to Forage Area 2, allowing ants to explore the entire habitat. The astronaut then set the video camera to record ant movements in this “condition” for approximately 30 more minutes.

Video of the ants was transmitted back to NASA on Earth and is available here on BioEd Online (www.bioedonline.org). Investigators are using a software program specifically designed to track the movement patterns and interaction rates of the “space” ants. When available, their findings will be provided here, enabling students and other investigators to make direct comparisons of the flight ants with their own Earth-based ants living in habitats they constructed. Instructions for building ant habitats with similar dimensions to those used on the ISS can be found here.

Experiment results could provide insights into how ants regulate their social interactions under normal (Earth) gravity conditions and whether these interactions are dependent on gravity. Also, very little is known about how ants control or modify path shape, and the investigation could provide clues about conditions under which ants forage in a random pattern or on a straighter path. Finally, the results could shed light on how ants coordinate their behaviors. It may even have applications for other systems that rely on distributed algorithms, such as robots deployed for search and rescue operations.

For more information on expandable search networks, such as those used by ants, see Dr. Deborah Gordon’s website at Stanford University (http://www.stanford.edu/~dmgordon).