Animals communicate using a complex language of chemical signals that governs many aspects of their lives. These messages, which can travel through air and water or be deposited on surfaces, are a fundamental way organisms interact with each other and their environment. The effectiveness of chemical signals lies in their ability to convey information over long distances and to linger long after the sender has departed, shaping social structures and survival strategies.
Types of Chemical Signals Used by Animals
The vocabulary of chemical communication is composed of various signals, categorized by whether they are used for communication within a species or between different species. The most well-known are pheromones, which are chemical substances that trigger a response in other individuals of the same species. This form of intraspecific communication ensures that the message is understood only by its intended audience.
Pheromones can be grouped by the responses they elicit. Releaser pheromones trigger an immediate behavioral change, such as sex attractants used by moths, alarm signals released by ants, or trail markers that guide colony members to food. Primer pheromones cause slower, long-term physiological changes, such as a pheromone from a queen bee that suppresses the reproductive development of worker bees.
Animals also use allelochemicals to interact with members of different species. These interspecific signals are classified based on who benefits. Kairomones benefit the receiver but are disadvantageous to the sender, such as the scent of prey that a predator uses to locate it. Allomones benefit the sender, like a skunk’s defensive spray. Synomones are mutually beneficial, such as floral scents that attract pollinators.
How Animals Produce and Perceive Chemical Cues
The ability to send and receive chemical messages relies on specialized biological systems. Animals produce these signals in a variety of ways, often through dedicated exocrine glands that release substances to the exterior of the body. These glands can be located on the face, hooves, or near the anus in many mammals and are used to mark territories or signal social status. In insects, pheromones may be produced by glands on the abdomen, legs, or wings.
Signals can be released into the environment by being carried on the air, dissolved in water, or deposited directly onto a surface. Many mammals use urine or feces as a medium for their chemical messages, creating scent posts that delineate their territory. This marking communicates the owner’s identity, sex, and reproductive status to any other animal that encounters it.
Perception of these chemical cues is equally specialized. In insects, chemoreceptors are located on the antennae, feet, or mouthparts, allowing them to “smell” airborne molecules or “taste” chemicals. Vertebrates primarily rely on an olfactory system, where airborne molecules are detected in the nasal cavity. Many vertebrates also possess a vomeronasal organ (VNO), specialized for detecting less volatile cues, such as those involved in reproduction. The flehmen response seen in animals like cats and horses helps draw these signals into the VNO for analysis.
Insect Pheromone Examples
Insects provide clear examples of chemical communication, relying on pheromones to coordinate their lives. Ants are masters of chemical trails, using pheromones to guide nestmates with precision. When a foraging ant finds food, it lays down a trail of pheromones on its way back to the nest. Other ants detect this trail and follow it to the food, reinforcing the scent on their return trip.
Female moths release a species-specific sex pheromone that can be detected by males from miles away. The male moth’s antennae are exquisitely sensitive, allowing him to fly upwind along the concentration gradient to locate the female. This system is so effective that synthetic pheromones are used in traps to monitor and control pest populations.
Honeybees utilize a complex chemical language to maintain social order. The queen bee produces a “queen mandibular pheromone” that is distributed among the workers. This pheromone inhibits the ovarian development of worker bees, prevents them from raising new queens, and acts as a sex attractant during her mating flights. Honeybees also use alarm pheromones; when a bee stings, it releases chemicals that alert other bees to the threat and can provoke a coordinated attack.
Mammal Pheromone Examples
Mammals have a sophisticated chemical vocabulary centered on marking territory and communicating social and reproductive status. Canids, such as wolves and coyotes, use urine to create “scent posts” that convey the sex, health, and social status of the individual. Domestic dogs retain this behavior, using scent to gather information about other dogs in their neighborhood.
Rodents live in a world dominated by scent, and their urine contains a complex cocktail of chemicals that signals individual identity, dominance, and reproductive readiness. These pheromones can have profound physiological effects. For instance, chemicals in a dominant male’s urine can accelerate puberty in young females or terminate the pregnancies of females mated with a rival.
Many large mammals use chemical signals to coordinate reproduction. Female crabs and mule deer release chemical cues in their urine to signal their readiness to mate. Male mule deer can identify their own mothers by the specific scent produced by glands on their legs. Some animals, like antelope, deposit feces in specific locations to create visual and chemical markers of their territory.
Allelochemicals in Interspecies Communication
Allelochemicals mediate relationships between different species, such as those between predator and prey or plants and pollinators. These signals are classified based on which organism benefits from the communication.
Kairomones
Kairomones benefit the receiver at the expense of the sender. For instance, a predator uses the scent of a prey animal to locate it. Some parasitic insects also detect the sex pheromones of their host species, using the signal to find a suitable place to lay their eggs.
Allomones
Allomones benefit the sender. Many plants produce repellent compounds to deter herbivores, while a skunk’s defensive spray repels threats. Some orchids even produce allomones that mimic the sex pheromones of female wasps, tricking males into pollinating the flower.
Synomones
Synomones are mutually beneficial to both parties. A common example is the floral scents released by plants to attract pollinators. The plant achieves pollination, and the insect is rewarded with nectar, a vital food source.