The beetles are an insect group part of the Coleoptera order. This order contains more species than any other order, constituting almost 25% of all known animal life-forms, with about 400,000 species of beetles, and more being discovered frequently. This makes the beetle group a very diverse one. They can be found in all types of habitats, with the exception of the polar one and have multiple effects on the ecosystem, due to theirs interaction with their plant and fungi food source, the invertebrates they sometimes eat, or the animal or plant debris break down they cause. Some beetles are considered agricultural pests, while others are quite useful and act like important controls of other agricultural pests.
Description and distribution of beetles
Most beetle species are characterized by a hard exoskeleton and hard forewings. The exoskeleton is formed by multiple plates separated by thin sutures, which act as an armored defense, while still offering the insect flexibility. As with all other insects, the anatomy of the beetle is divided into three main sections: the head, the thorax and the abdomen.
The head contains the mouthparts which are projected forward, are quite thick and vary in size depending on the specie. They are similar to the grasshopper’s mandibles, that move horizontally to grasp, cut or crush food. These differ in size depending not only on the specie, but also of the gender. The eyes are compound and display remarkable adaptability. There are species with divided eyes or even ocelli, which are small, simple eyes, placed further back on their head. The antennae of the beetles are mainly used for smell, but also help the insect feel the surrounding environment physically. They vary greatly in form from male to female, and especially in the whole Coleoptera order.
The thorax is the body part from which all three pairs of legs and both pairs of wings arise, and the abdomen is everything that comes posterior to the thorax, made up of a series of rings, each with a hole for breathing and respiration.
As beetles mostly communicate through pheromones, different glands specialize for different pheromones produces for finding mates. A notable number of species have also developed special glands to produce chemicals for deterring predators. These defensive glands located at the end of the abdomen, release a variety of substances through an explosive ejection, meant to keep predators away.
When it comes to their diversity, it must be noted that beetles are the largest order of insects, with their 400,000 species spread all over the world. Around 500 families and subfamilies can be recognized, however the entire beetle fauna in not equally well known in all parts of the world, as their diversity is estimated differently in places like Australia or North America. Coleoptera are found in nearly all natural habitats, including freshwater and marine habitats, everywhere vegetative foliage is found, from trees and their bark to flowers, leaves, and underground near roots, and even inside plants in galls, in every plant tissue, including dead or decaying ones.
Breeding and dietary information
Beetles, as most other insects, go through a four stage metamorphosis process: the egg, the larvae, the pupa and the adult. The larvae are called grubs and the pupa is called the chrysalis. In some species, the pupa may be enclosed in a cocoon constructed by the larva towards the end of its final instar.
When it comes to mating, beetles can display a very detailed behaviour, which has as its basis a communication through pheromones. Different species use different types of chemicals for their pheromones, as they communicate and locate their mate through them. they can also use biosynthesized light or even a mating call, in the case of fireflies. Before mating, both male and female present different types of behaviour, as they vibrate the objects they are on, or the mate climbs onto the back of the female and strokes his antennae on her head. It is also known that many male beetles are very territorial, defending their patches from intruding males. When conflicts arise, the strongest and fittest will remain victorious.
After mating, a single female can lay up to several thousand eggs in one lifetime. They are usually laid according to the substrate on which the larvae will feed after hatching. They are laid in clumps on leaves, buried in the surrounding medium or be individually attached on plants. Not all species provide the same amount of parental care, as some beetles construct complex underground structures to supply shelter and food for their young ones, while others just bite sections of leaves to curl them inwards, and lay the eggs there.
When the eggs hatch and the larvae emerge, they tend to feed voraciously. Some feed on plants, while others feed within their food source. Same as the adults, the larvae of many species are also predatory, and can be distinguished by their dark heads and chewing mouthparts. They are highly mobile and resemble hardened worms. This stage is the longest for the beetle, being possible to last even several years. All beetle larvae go through several instars, which are the developmental stages between each moult. In many species, the larvae simply increase in size with each successive instar as more food is consumed.
When its time for their next stage, the beetle larva pupate, and from these pupae, fully transformed, sexually mature adults emerge. Depending on the specie, they have different lifespans, that can range from weeks to years.
As they variety of species is so great, beetles are able to take advantage of a great diversity of food sources they can find available in their world wide habitat. Some beetles are omnivores, having a diet based on animals and plants as well, while others are specialized in a single plant, feeding only on that specific one. Some species, such as the ground beetle and the rove beetle are primarily carnivorous, having a diet based on snails and earthworms. Many species also feed on decaying organic matter, ranging from dung, to dead animals.
Beetles as pests
As around 75% of all the beetle species are having a diet based on plants, both as larva and as adults, they can be highly considered pests. On the other hand, some species can also be beneficial to crops, mainly by controlling populations of other pests. The best known type of beneficial beetle is the ladybug, as is feeds on scale insects and mealy bugs, on aphid colonies and also small caterpillars. Ground beetles are common predators of many different insects and other arthropods, including fly eggs, caterpillars, wireworms, and others. Dung beetles have also successfully reduced populations of flies and parasitic worms that normally breed in cattle dung. They play an important role in agriculture, as they not only combat pests, but also, burying and consuming dung, they improve nutrient recycling and soil structure.
However, as pests, beetles can be dangerous to crops and annoying to humans. In both the larval and adult stages, beetles live in or on plants, wood, fungi, and a variety of stored products, including cereals, tobacco, and dried fruits. Species such as the boll weevil which feeds on cotton buds and flowers, can easily spread throughout the country and affect a lot of cotton crops. In the 1920s it created a lot of damage, remaining the most destructive cotton pest in America. Many other species, such as the bark beetle, elm leaf beetle and Asian long-horned beetle, can cause a lot of damage to plants such as elm trees, as the bark beetle can also carry the Dutch elm disease, as they move from infected breeding sites to feed on healthy elm trees. This has lead to the devastation of elm trees, especially in Europe and North America.
As a pest for crops, the Colorado potato beetle is one of the worst, as it has also developed an immunity to pesticides. Crops are being continuously destroyed, while the beetle has begun to develop resistance to all the pesticides used against it. They can also affect tomato, eggplant and capsicum, not only potatoes.
Inside the house, beetles can also cause damage, by attacking the wooden buildings, or the furniture you have inside your house. The the death watch beetle is a wood-boring beetle that attacks hardwoods such as oak and chestnut and begins its influence at the time of construction. The carpet beetle is drawn to fibers, so to protect your clothing, you will need to keep your clothes off the floor, store un-used clothing in plastic bags or containers and dry clean clothing before storing it. They can be found in found in attics, wool carpets, tapestries and wall-to-wall carpeting, but they can also eat dead insects, furs, hides, feathers, horns, hair, silk and bones.
Some beetles also act as parasites, living both as a larva and as an adult, feeding on epidermal tissue and possibly on skin secretions and wound exudates, on several animals. There are also beetles that infests honey bee hives, with the larva digging a tunnel through the comb, towards the stored honey and pollen, thus damaging the comb and the honey in the process. Larvae defecate in honey and the honey becomes discoloured from the faeces, which causes fermentation and a frothiness in the honey; the honey develops a characteristic odor of decaying oranges. Damage and fermentation cause honey to run out of combs, destroying large amounts of it both in hives and sometimes also in honey extracting rooms.
Beetles can also help pollinate some types of flowers, which are usually large, greenish or off-white in color, and heavily scented. These species are mostly found in South Africa, but also southern California as well.
When it comes to their relationship with humans, it is known that around 44 species are known to be used as food, usually eaten in the larval stage, with the most common species being the mealworm, and the larvae of the darkling beetle and the rhinoceros beetle.
Depending on the type of species you encounter, you will need to know if it is a beneficial type of beetle, or you have your hands full with an infestation which can become quite a nuisance. For more details on how to prevent such infestations, visit our related article about “Preventing beetle infestations“, where you will find methods of prevention and ways in which you can protect your crops from these pests. However, if the infestation has already occurred, try to determine the type of beetle you are dealing with, and then, based on the advice and extermination steps shown in our article about “How to get rid of a beetle infestation”, win back your crops, yard or home, and then make sure you always apply preventive measures, as prevention is the best way of getting rid of any type of pests.