Foraging for food is an essential premise of a Bug’s Life – the ants have to collect enough food to feed the grasshoppers and get food for themselves. The movie got some parts of this process right – ants do often travel in a line to get from a food source to their nest – but the process is much more impressive than just following the leader.
To harvest food, ants use a combination of several different sensory systems – smell, sight, and touch.
Ants have four to five times more odor receptors than most other insects. It is unclear whether all 400 ant genes for different olfactory receptors are actually expressed but this allows ants to distinguish several different scents. For comparison, humans have 1000 genes for different olfactory receptors (proteins to detect chemicals) but only 350 to 400 of them are actually found in cells. Ants use these odor receptors to sense the presence of food up to several meters away depending on the species, but more importantly, they use these odor receptors to detect pheromones.
Pheromones are chemicals secreted by ants (and several other insects and animals) for a variety of purposes. Whereas many mammals secrete pheromones to mark their territory, ants secrete pheromones to mark a trail towards food (as well as to recognize each other, attract mates, and signal alarms such as when an ant dies). Other ants will detect these chemicals with their own antennae and follow the trail towards food and back towards their nest.
Detecting pheromones is important for the emergent process of how ants form lines – it isn’t because they are watching other ants with their eyes or because they are programmed to follow each other. Ants can more easily detect pheromones along trails that have the strongest pheromone scent. Ants who travel on shorter trail between the nest and food can make more trips in an hour than ants traveling along longer trails, which means the shorter trails will have more pheromones deposited due to the path being more heavily traveled.
This is kind of like how humans try to find information online. If a page is particularly useful, it will get more page visits. With more visits to a page, a website’s ranking in Google searches increases which makes it easier for additional people to find the information they need – this shortens the path from search to result because this is the path that other people have traveled.
How do ants get back home?
In addition to leaving pheromone paths, ants use sight and touch to get back home as well. These senses come in handy especially when an ant has traveled a far distance and their pheromone scent has dissipated and is more difficult to detect. When an ant is searching for a new food source, they store images of their path so that they can identify landmarks on their return journey.
Ants also know where their home is based on the sun’s position. Researchers were able to help ants that were traveling backwards, pulling a cookie crumb that was too big to carry moving forwards, find their way back home by adjusting where light was coming from. This suggests that ants have an understanding of their general position in their surroundings.
Additionally, ants are believed to be able to count their steps and keep track of changes in direction on their path when searching for food. Researchers have tried several ways of disrupting this ability with little success, which has promising applications for programming robots to navigate dangerous areas.
Furthermore, there is research that suggests that ants may be able to detect magnetic fields and vibrations because placing magnets near nests serves as an identifier for ants: they sometimes search for their nest based on this cue.
Can ants sense when it is going to rain?
The ants in the colony in a Bug’s Life had to collect enough food before the rainy season. This and the frequent observation that ants leave their nests around the time of rainstorms suggests that ants have some way of knowing when it is going to rain, but is this based in any scientific fact?
Currently, there is no definitive evidence that ants can detect changes in the weather, but they have other interesting behaviors. Most ant species actively forage at times of day and seasons specific to their species. Most of these behaviors are due to ants’ abilities to detect temperature and atmospheric moisture changes. Because ants do not have blood but instead free floating fluid called hemolymph, they have to regulate their body temperature based on external factors. Small changes in moisture affect ants’ abilities to bend their joints, so they might remember that this correlates with rainstorms.
According to Dr. Kirsti Abbott, ants may be able to detect changes in air pressure through their breathing mechanism – holes in their exoskeleton called spiracles. Because drops in air pressure frequently precede rainstorms, ants may learn this association as well.