Why Do Insects Communicate With Pheromones?
In the insect world, chemical substances called "pheromones" are the dominant means of communication instead of vocal language. Pheromones are a collective term for volatile chemical substances that transmit information between members of the same species. They are secreted from glands on an insect's body surface, dispersed into the air, and detected by olfactory receptors located on the antennae of the receiving insect. Compared to human olfaction, insects' chemical senses are remarkably acute, with some species capable of responding to pheromones at the level of just a few molecules.
There are two main reasons why pheromone communication evolved in insects. First, many insects have more developed chemical senses than vision or hearing, allowing them to function in dark environments such as at night, in dense forests, or underground. Second, chemical signals are persistent and remain in space even after the sender has departed, enabling information transmission across time intervals. Due to these characteristics, pheromones have evolved as a cornerstone of reproduction, defense, and social behavior.
Sex Pheromones: The Chemical Language of Successful Reproduction
Sex pheromones are the most extensively studied pheromones and play a role in attracting individuals of the opposite sex to promote mating. In many insects, females secrete and males detect these pheromones, though in some species the reverse occurs. The "bombykol" secreted by female silkworm moths (Bombyx mori) can be detected by males from several kilometers away even at concentrations below 100 ng, making it a well-known example symbolizing the high sensitivity of sex pheromone detection.
The concept of sex pheromones can also be applied to the care of beetles and stag beetles. As mature females begin feeding after emergence (post-emergence feeding), the amount of sex pheromone they secrete increases, making males more active. When performing pairing in captivity, it is important to confirm that the female has undergone sufficient post-emergence development and feeding.
If males and females are placed together before the female begins post-emergence feeding, males may court but females will merely flee, resulting in cases where mating does not occur.
Aggregation Pheromones: Gathering and Securing Food Resources
Aggregation pheromones have the function of gathering individuals of the same species in a specific location. It is believed that when beetles and stag beetles that feed on tree sap gather at oozing tree sap sites, aggregation pheromones secreted by earlier arrivals are partially attracting them.
This mechanism is also well-developed in social insects such as honeybees and ants, where workers recruit nestmates through recruitment accompanied by aggregation pheromones when they discover food sources. The tendency of crickets to congregate in specific corners of a rearing cage may also be influenced by aggregation pheromones.
By understanding this behavior, placing multiple hiding places (such as egg trays) that crickets prefer within the cage can distribute and reduce cannibalism caused by overcrowding.
Alarm Pheromones: Instant Signals Conveying Danger
Alarm pheromones are released by individuals sensing danger and trigger defensive behaviors such as fleeing or attacking in other members of the same species. While well-known in ant and honeybee colonies, they are also observed in solitary insects.
In captive management, these alarm pheromones provide practical hints. For example, when a cricket rearing cage is suddenly opened or exposed to bright light, all the crickets may thrash about at once; this is a combined behavior resulting from alarm pheromone release and direct stimulation. Feeding and cleaning should be done with slow, deliberate movements and without startling the insects, which helps prevent escapes and reduce individual stress.
Territorial Pheromones: Space Monopoly and Competition
The intense fighting between males of stag beetles and beetles in a cage is suggested to involve territorial pheromones and competitive signals. In particular, Japanese giant stag beetles and flatheaded stag beetles are extremely aggressive toward males of their own species, and when multiple males are housed together in the same cage, injuries such as broken mandibles and missing legs frequently occur.
While this involves not only pheromones but also visual and tactile stimuli, empirical experience shows that attacks intensify particularly when a new individual is introduced to a cage where chemical traces of the previous inhabitant remain. When changing cages, completely replacing the used substrate to reset pheromone traces makes it easier to introduce new individuals. Additionally, if males chase females after pairing, separation is the standard approach. Female beetles in an egg-laying setup tend to focus better on egg-laying in an environment without male pheromones.
Practical Applications for Pet Care
Applying insights from pheromone biology to captive care leads to the following practical advice.
Timing Management for Pairing: The peak of sex pheromone secretion is thought to occur 2–4 weeks after females begin post-emergence feeding. Performing pairing during this period increases mating success rates.
Strict Individual Housing: Keeping same-species males in separate cages prevents not only fighting but also eliminates chemical and behavioral stress related to territorial disputes. Stress impacts individual lifespan.
Cage Cleaning and Residue Reset: When moving females after egg-laying is complete or introducing new males, completely replacing the old substrate and removing pheromone traces from previous inhabitants ensures smooth transitions.
Environmental Stability: To avoid triggering alarm pheromones, feeding and observation should be done quietly and lighting changes kept to a minimum. In particular, nocturnal beetles and stag beetles are active at night, so ideally observations should be done under dim lighting for short periods.
At br-choku, you can purchase healthy adult and larval insects from breeders knowledgeable about such ecology. Starting care with an understanding of how pheromones and instinctive behaviors work leads to higher breeding success rates and reduced individual loss from fighting and stress.
