Have you ever felt uncomfortable when hearing this expression or feared to find your bed infested with bed bugs? Yes, bed bugs exist. However, good news is that not all insects known as ‘bugs’ sting nor live inside our bed sheets.
What bugs really are? Are all of them harmful? Where can we find them? Find out their diversity through this post, and give up thinking that bugs are dangerous!
Which insects are called ‘bugs’?
When talking about ‘bugs’, people are unconscious about the true diversity of these organisms. Bugs, and more exactly true bugs, belong to the Heteroptera suborder, which includes more than 40,000 species worldwide; in fact, they are the largest group of insects with simple metamorphosis. Their most ancient fossil, Paraknightia magnífica, which was found in Australia, has been dated from the late Permian (260-251 MA).
The Heteroptera belong to the Hemiptera order, inside which we can find other suborders which were formerly classified as a single suborder (‘Homoptera’). Some of the suborders once classified as ‘Homoptera’ include some well-known organisms, such as cicadas (Cicadidae) and aphids (Aphididae).
How can we recognize them?
Heteropterans appear in different forms and sizes. The tiniest specimens belong to the Anthocoridae, Microphysidae, Ceratocombidae, Dipsocoridae, Aepophilidae and Leptopodidae families, which are barely visible to the naked eye. Among the largest members there are some species of the Belostomatidae family, such as Lethocerus indicus (6.5-8 cm length). Despite this, they appear as a monophyletic group according to molecular data.
They show at least three synapomorphies:
- Piercing-sucking mouthparts, long, forming a stylet.
Mouthparts of the predator Arilus cristatus (Reduviidae). Picture property of John Flannery on Flicker (CC 2.0). - Paired odoriferous glands.
- Four-segmented antennae.
Furthermore, they have forewings (formally known as hemelytra) with both membranous and hardened portions, which gives its name to the group (Heteroptera, from the Ancient Greek ‘hetero’, different; ‘-pteron’, wings).
Ecology
Life cycle
Heteropterans undergo a simple metamorphosis, so youths or nymphs and adults almost show no differences and cohabit in the same habitat. After hatching, nymphs molt several times until reaching the last nymphal molt, known as imaginal molt, through which they reach adulthood.
Adults differ from nymphs on having wings, a new disposition of odoriferous glands openings, a different number of tarsal (legs) and antennal segments, ocelli, ornaments (spines and glandular hairs), sexual traits on the terminal abdominal segments and sometimes a different coloration, besides a bigger size and a way harder tegument.
Communication and defense
Specimens of the same species emit volatile pheromones produced by their odoriferous glands as a way of communication. So, they can expel aggregation pheromones and sexual pheromones to gather in a point or to find a mate, respectively. In some species, it has also been documented the emission of sounds produced by stridulation, that is, producing sounds by rubbing together certain body parts.
Heteropterans develop passive and active defense mechanisms:
- Among passive mechanisms, we can highlight the own body shapes (e. g., smooth and rounded structures which difficult their capture by predators), the inactivity as a way to go unnoticed by other organisms, and the crypsis or mimicry. Some examples of crypsis or mimicry are 1) color mimesis (homocromy) 2) shape mimesis (homotopy), through which they imitate structures of their environment, either plants or animals (e. g. ant-mimicry or myrmecomorphy) and 3) disruptive mimesis, that is, their outlines get blurred with the environment, so it gets difficult for predators to find them.
- Some active mechanisms are 1) escaping, 2) biting, 3) the detachment of some appendices to confuse predators and 4) the emission of stink or irritating substances by their odoriferous glands, which in most of cases they acquire from plants they feed on. Others emit stridulating sounds.
Life forms and diversity
Even though most people know something about heteropterans due to the famous bed bugs, feeding on blood is far from being the only life form among true bugs.
- Terrestrial
Most heteropterans inhabit terrestrial environments, either on plants or on the ground as phytophagous (they feed on vegetal fluids) or predators of other insects. There are also some terrestrial heteropterans that feed on roots or on fungi that develop under tree bark. Some examples of terrestrial phytophagous families are Pentatomidae and Coreidae. Among predators, which use their stylet to inoculate proteolytic agents inside their preys to dissolve their content and then suck it, there are a lot of members from Reduviidae family.
- Aquatic and semiaquatic
Aquatic and semiaquatic forms have special adaptations to live in water, like hydrofuge hairpiles which repel the water. Most of them live in lakes and rivers, either on their surface (semiaquatic) or submerged.
Semiaquatic species usually have long legs and long antennae, which together with the hydrofuge hairpiles let them to stand on water. Water striders (Gerridae), which are very abundant in Europe, are a clear example of this life form.
Aquatic species usually have a pair of legs adapted to swim. A good example of this are the members of the family Notonectidae or backswimmers, which have the hind legs fringed for swimming.
Despite living in water, aquatic heteropterans need surface air to breath, so they go out of water periodically. They present different strategies to absorb oxygen, such as swallowing air that goes directly to the respiratory or tracheal system through a siphon (Nepidae) or capturing air bubbles with their hydrofuge hairpiles (Nepidae). Other simply get covered of a tiny air layer using their hydrofuge hairpiles.
- Hematophagous
Finally, there are heteropterans that feed on blood and live as bird and mammal parasites. This is the case of the Cimicidae family (e. g. Cimex lectularius, the bed bug) and some groups of Reduviidae, such as the members of the subfamily Triatominae, which are also known for being vectors of the Chagas disease in the center and south of America (being Triatoma infestans its main vector).
Scientific interest
- They help to regulate some wood and crop pests, having an important role in integratative pest management. This is the case of some predator heteropterans from the Reduviidae, Anthocoridae, Miridae, Nabidae and Geocoridae families. However, some phytophagous heteropterans can act as pests too.
- They have been an interesting scientific model for the study of insect physiology.
- They are an important element on human diet in some countries, being Pentatomidae one of the most consumed families. Some aquatic heteropterans, such as Lethocerus sp. (Belostomatidae) are very appreciated as food in some Asiatic countries, like Vietnam and Thailand.
- Some of them are disease vectors or a cause of discomfort. The most classic example is the bed bug (Cimex lectularius), which has become a frequent pest in temperate regions; some Cimidae are also a threat for free range chickens and other farm birds. In America, Triatominae are vectors of different diseases, being the most famous the Chagas disease (transmitted by a protozoan, Trypanosoma cruzi).
. . .
All organisms on Earth are necessary for some reason: you only need to investigate about them. Even the true bugs!
References
- Goula M., Mata L. 2015. Orden Hemiptera: Suborden Heteroptera. Revista IDE@ – SEA, 53: 1–30.
- https://www.britannica.com/animal/heteropteran
- Schuh R. T., Slater J. A. 1995. True Bugs of the World (Hemiptera:Heteroptera): Classification and Natural History. Cornell University Press.
Main picture property of Pavel Kirillov on Flickr, with license Creative Commons 2.0. (link).
All you need is Biology 