One of the four ways that animals communicate is through chemical communication. They do this by using pheromones. A pheromone is a chemical secreted by an animal to trigger a specific reaction from other animals.
Invertebrates most commonly use pheromones; however, most animals produce them. Birds are the only animals where pheromones are not used. Pheromones can be used to attract a mate, as a means of defense, mark territories, or in the case of bees, co-ordinate large amounts of workers. Farmers are turning to pheromones as a more humane way of tackling pests on their crops.
These are just some of the ways that animals use chemical communication, and there are some more fascinating ways below.
What Are Pheromones?
Pheromones are either released into the air or are produced in bodily fluids such as sweat, urine, or saliva. Experts have concluded that insects may use as many as one hundred different pheromone combinations throughout their life. Certain chemicals elicit different responses depending on the concentration of each chemical and whether they are combined with other chemicals.
Unlike sound, pheromones do not fade over time or lose their effectiveness. Male moths have been known to follow pheromone trails for miles searching for the female producing the pheromones.
Aggregation and Reproduction
Aggregation refers to a large group of animals, either of the same sex or both sexes. Pheromones are most often used within large groups of animals.
Bee colonies use pheromones to coordinate their everyday life. The queen bee controls the behavior of her colony by releasing pheromones throughout the nest. The pheromones she produces have several functions.
Firstly, her pheromones keep order within the nest or hive as the pheromones alert the colony that their queen is healthy and can still lay eggs.
Secondly, the queen’s pheromones prevent other bees from laying eggs. Only the queen can fertilize eggs as she stores sperm in her spermatheca. Eggs she does not fertilize will develop into male drones. Eggs she does fertilize will become female worker bees. The role of the drone is simply to mate with a new queen, and they die shortly after.
Female workers keep the nest of the hive in good condition, feed the young, care for the queen, collect resources such as nectar and produce food for the colony. Without the queen’s pheromones, all worker bees would start laying eggs, but they would all be male drones, as only the queen can fertilize eggs. This would cause the eventual death of the colony as male drones are a drain on resources.
The queen’s pheromones also attract male drones when she takes her first and only flight from the nest. A new queen will mate with as many as 20 drones, collecting their sperm to fertilize all the eggs she may lay in her lifetime. Her pheromones draw males to her and inform them that she is receptive to mating.
Female mealworm beetles release sex pheromones to attract male beetles; however, once the first male finds and mates with her, he covers her in his pheromone, which dissuades other males from mating with her.
This tactic ensures that only the first male can pass on his DNA to the female. If he does not use his pheromone or does not use enough of it, other males will also mate with her.
While pheromones are most often attributed to insects, mammals also use them. Pigs and boars have one of the highest numbers of olfactory receptors of any species. They can detect scents in far lower concentrations than humans.
Pigs and boars use pheromones to signal their reproductive state. A female in oestrus will emit pheromones to attract males to mate with her. The male will produce a sex pheromone in his saliva, which is believed to trigger the female to adopt a more receptive body position so the male can mate with her.
Chemical Communication For Defence
Monarch butterflies are probably the most recognizable among western species. The bright orange coloration and large eye markings make them quite easy to spot. Unfortunately, this also makes them easy targets for predators.
So how is it that there are so many monarch butterflies? The answer is pheromones. To deter predators, monarch butterfly caterpillars only eat the leaves of milkweed plants. These plants emit pheromones that have a very bitter taste. When predators try to eat a monarch butterfly caterpillar, they will immediately spit them back out as the taste is overpowering.
This allows the caterpillar to complete their growth and metamorphosis to become an adult butterfly.
Some moth species also use this same technique. Females during the larval stage will feed on plants containing alkaloids that are poisonous to other animals. She keeps these alkaloids when she metamorphoses into an adult, and she also can pass the alkaloids to her eggs. This prevents them from being eaten by predators.
Bombardier beetles have by far the most dramatic use of pheromones for defense. Thomas Eisner, the father of chemical ecology, discovered that bombardier beetles have two chambers within their body. One chamber stores hydrogen peroxide, and the second store’s hydroquinone.
When a bombardier beetle feels threatened, they spray these chemicals from their rear. As the two chemicals combine, the resulting exothermic reaction creates an acid spray at boiling temperature, deters or even killing any potential predators.
European wood ants have a similar defensive strategy. Whenever a predator attempts to feed on the colony, the ants all begin to spray an acidic substance into the air. This substance stings like the prickles of a nettle bush, driving away from the predator. The acid produced by wood ants has such an acrid smell that even humans can detect it.
Most mammalian species use some form of pheromone to mark their territory. Males will travel the edges of their territory, spreading their pheromones onto tree trunks, logs, and rocks. This is done either by spraying urine or by rubbing the face onto certain surfaces.
Many cat owners will understand that an intact male cat will spray all over the house. He does this to mark the house as his territory to prevent other male cats from entering. Typically, having a cat neutered will reduce or stop a cat from spraying.
When you take your male dog for a walk, you probably notice that he usually urinates where other dogs have. Dogs use their urine to inform other dogs that they are in the area. When female dogs urinate, male dogs can detect whether the female is in oestrus and ready to mate.
Whenever you see your dog sniffing a urine patch and then quivering its lip, this indicates that your dog is receiving messages to his brain from the other dog’s urine. This includes things like age, gender, and reproductive state.
Some animals will spread their pheromones by scratching at tree trunks. This is seen in animals such as bears and wild cats.
While males use pheromones to mark their territory, females will follow these trails to find the territory owner. Females are also capable of recognizing different pheromones belonging to individual males and even remembering the location of each male’s pheromone marks.
In certain insect species, females will mark the location of their eggs with pheromones to stop other females from laying in the same location. This prevents resource competition between clutches once the eggs hatch.
Pheromones For Pest Control
In recent years, it has become increasingly popular within the farming industry to use insect pheromones to control pest insects rather than spray expensive and damaging insecticides. Spraying a crop area with pheromones makes it difficult for males to find females, so mating is drastically reduced.
This decreases the number of adult insects with the ability to reproduce and allows farmers to better protect their crops from pest species.
Since pheromones only control behavior and do not kill insects as pesticides do, they are considered a better approach from a welfare perspective.
Pheromones are also used in domestic homes and businesses to trap pest insects. Flypaper and boxes use pheromones to attract insects. When the insect lands on the paper, they stick to the tacky substance. Once the traps have caught all the insects in the home, the paper or box can then be disposed of.
This does not prevent other insects from entering the home, but it does provide an easy and clean way of catching and removing them. This is particularly helpful to people who cannot use insect spray due to respiratory conditions such as asthma.
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