Sleep tight, don’t let the bed bugs bite!

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:

1. Piercing-sucking mouthparts, long, forming a stylet.

   

   Mouthparts of the predator Arilus cristatus (Reduviidae). Picture property of John Flannery on Flicker (CC 2.0).

2. Paired odoriferous glands.
3. 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).

Pentatomidae. The proximal part of forewings is hardened, while the distal one is membranous. Picture property of Mick Talbot on Flickr (CC 2.0).

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.

Life cycle of heteropterans. Picture property of Encyclopedia Britannica, Inc. (link).

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.

Nezara viridula nymph (Pentatomidae), still wingless. Picture property of S. Rae on Flickr (CC 2.0)

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.

Leptoglossus occidentalis (Coreidae), with their wide tibiae that look like leaves. Picture property of Giancarlodessi (CC 3.0).

Myrmecoris gracilis (Miridae), a clear example of ant-mimicry or myrmecomorphy. Picture property of Michael F. Schönitzer (CC 4.0).

• 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.

Water striders (Gerris sp.). Picture property of Webrunner (CC 3.0)

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.

Notonecta sp. (Notonectidae). Picture property of Jane Burton/Bruce Coleman Ltd. (link).

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).

Cimex lectularius or bed bug nymph. Public domain.

Triatoma sp. (Triatominae). Picture property of Bramadi Arya (CC 4.0).

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.

Lethocerus sp. Picture property of Judy Gallagher on Flickr (CC 2.0).

• 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).

Animal mimicry: now you see me…

What do you see in the picture above? Maybe snakes… or maybe not? All animals try to enhance their survival rates, and one of the most effective ways to achieve this goal is by looking similar to some environmental elements, either by camouflaging or by imitating traits from other organisms. Mimicry is a complex and surprisingly phenomenon present in almost every animal taxa acting as an evolutionary driving force. Do you know what types of mimicry exist and which animals do perform each one? Are you ready to read more about this topic? If that’s the case, keep reading!

Mimicry vs camouflage (or crypsis)

The word mimicry (that derives from the Greek term mimetikos = “imitation”) was firstly being used to describe people who have the ability to imitate. From 1851 on, its use extended to other life forms.

Sometimes, the term mimicry is used as a synonym of “camouflage or crypsis”. Although these two words are sometimes confused and used equally, from a biological point of view they are well differentiated terms:

• Mimicry: the ability an organism develops to imitate one or more traits from another organism (with which it’s unrelated) so that it can obtain some benefit.

• Camouflage (or crypsis, from the Greek word kryptos = “hidden”): the ability an organism has to be unnoticed by its predators (or prays) by copying some environmental traits or by developing a disruptive coloration that allows it to hide.

Some authors consider that camouflage includes only to the ability an animal has for imitating morphological traits from some environmental elements, such as different natural surfaces, plants or even sessile animals (i.e. immobile animals) like corals and sponges (as you can see on the picture below). On the other hand, mimetic animals go further and try to imitate not only morphological traits, but physiological and behavioral, looking for a response from other animals.

Can you see the camouflaged seahorse? (Picture by Stephen Childs, CC).

To sum up: the main objective of mimetic animals is to trick the senses (e.g. sight, hearing, smell…) of the other organisms they live with, in order to induce them a specific behavior that gives mimetic animals a benefit in return.

Types of mimicry

There are different ways to classify the different types of mimicry, but I will show you two main groups of mimicry, in which we will see different subtypes: defensive mimicry and non-defensive mimicry.

Defensive mimicry

The defensive mimicry is specially performed by animals that have lots of predators, so their survival rates depend on avoiding their predators.

BATESIAN MIMICRY

Venomous and poisonous animals tend to develop flashy traits (especially flashy morphological traits, like coloration and menacing sounds) which alert other animals about their danger. This phenomenon is known as aposematism (when an animal has a flashy coloration we talk about aposematic coloration). In the Batesian mimicry, the mimetic organism (that is usually harmless and edible) copies the flashy traits of a venomous or poisonous organism present in its habitat in order to make predators think it’s a harmful species. Thus, the mimetic organism avoids being caught and eaten by predators.

Poisonous Coral Snake (on the left) and non-poisonous Scarlet King Snake or False Coral Snake (on the right). The second one imitates the aposematic coloration of the first one (Source: oakdome.com).

 

MÜLLERIAN MIMICRY

Sometimes, there are various poisonous or venomous species coexisting at the same time in the same habitat that are all being very hunted by predators (and sometimes by the same predator). In some of these cases, even when only one of these species has an aposematic trait to dispel predators, the rest of them try to mimic it and develop this trait (or traits). In contrast with de Batesian mimicry, in this model all species are harmful at some degree.

Try to think that all these species finally develop the same aposematic coloration: when predators prey on one of these species and are harmed in result, probably they won’t attack again any species that has the same coloration pattern. Thus, predation pressure will be distributed within the species matrix.

Different geographical forms of both Heliconius erato (top row) and Heliconius melpomene (bottom row). Heliconius melpomene is a widespread neotropical species well known for its geographic diversity in color pattern. Throughout its range, H. melpomene is co-mimetic with Heliconius erato (which is generally less abundant than H. erato). Both have a disgusting flavor when being eaten (source: heliconius.org).

 

MERTENSIAN MIMICRY

This is an unusual type of mimicry (only a few cases in snakes are known), and it occurs when a harmful species copies an aposematic trait (e.g. coloration) of a less dangerous organism. What could this mechanism be useful for?

In the picture above, we can see that predators that feed on a harmful organism die (e.g. because it’s poisonous), so that the information “this animal is poisonous and mortal, don’t eat it!” won’t be transmitted to the rest of the predator population nor the next generations of predators. Thus, this harmful prey will remain preyed by predators. On the other hand, predators that feed on a less harmful prey and stay alive will have the chance to transmit this information to the rest of the population, so that predators will stop feeding on this prey.

In light of this situation, what do the most harmful organisms do? they try to imitate the aposematic traits of less harmful organisms (like coloration or shape) so that predators that feed on these less harmful organisms and stay alive, learn that all organisms with the same traits are dangerous. So, the predation pressure will fall for all preys.

Non-defensive mimicry

One of the most important types of mimicry within the non-defensive mimicry is the Peckhammian mimicry.

AGRESSIVE OR PECKHAMIAN MIMICRY

Unlike defensive mimicry, in this case are predators (or parasites) the ones that develop the traits of a more or less harmless species (or even of a beneficial one) in order to be unnoticed by their preys or hostages.

Plagiotremus rhinorhynchos (on the right) is an aggressive mimetic species that imitates another fish known as Laborides dimidiatus or bluestreak cleaner wrasse. Plagiotremus rhinorhynchos (family Blenniidae) imitates youth specimens of Labroides dimidiatus (family Labridae) both morphologically and behaviorally. Many species of fishes enter corals in order to be cleaned from parasites by Labroides dimidiatus. Taking advantage of this situation, P. rhinorhynchos get close to these coral fishes by mimicking the bluestreak cleaner wrasse in order to feed on their tissues (Pictures: the left one by Karelj, CC  and the right one by JennyHuang, CC).

Aggressive mimicry can be confused with some camouflage or crypsis mechanisms, as sometimes these two terms can be overlapped or maybe show no evident differences. This is the case of some abyssal fish species which have one or more filaments of their dorsal fins transformed into lures (sometimes these lures are bioluminescent). These lures sometimes mimic the shape of the abyssal fish’s preys, so those preys feel strongly attracted by them. Some authors propose that preys could be the model organisms and that abyssal fishes would modified their dorsal fin through an evolutionary process.

Abyssal fish on a photogram from the film ‘Finding Nemo’ (© Pixar, 2003).

Abyssal fish…a way more real than the one showed above (with its luminescent lure) (Image source: http://www.bogleech.com/nature/).

A curious case: the automimicry

The automimicry (also known as intraspecific mimicry) is a special case of mimicry that takes place when an organism transforms some part of its body in order to seems like another part of its own body or even of the body of another member of its species (e.g. a male that mimics a trait from females). The objectives of this type of mimicry are to obtain some benefit from other organisms or maybe to be unnoticed by their predators or preys.

The northern pygmy owl (Glaucidium californicum) has two big dark spots behind its head which remind of two big eyes (picture by Michael Durham).

Mimicry makes animals to evolve!

Mimicry is one of the processes that makes animals to evolve faster (do you want to learn more about evolutionary processes? Enter this link!).

These changes may occur in a higher or lower speed. So, what about those animals that mimic other organisms? Mimetic animals are in constant selective pressure to look more like their models in order to go unnoticed and improve their survival, but at the same time imitated organisms (the models) are also under selection to sharp their ability to discern between models and imitators.

.            .             .

Thus, mimicry is an incredible evolutionary engine: a perpetual struggle between mimetic organisms and imitated ones in order to improve their respective survivals.

REFERENCES

• Bone Q., More R. Biology of fishes. 3a ed. Taylor & Francis.
• Campbell, N.A., Reece J. B. 2007. Biología. Ed. Médica Panamericana.
• Cheneya K.L., N. Justin M. 2009. Mimicry in coral reef fish: how accurate is this deception in terms of color and luminance?. Behavoural ecology, Oxford Journals. Vol 20. P. 459-468.
• Harper D. Online Etymology Dictionary.
• Kashyap H. V. 2001. Advanced Topics In Zoology. Ed. Orient Blackswan.
• Sarmiento O.F., Vera F., Juncosa E. J. 2000. Diccionario de ecología: paisajes, conservación y desarrollo sustentable para Latinoamérica. Ed. Abya Yala.

Main picture source: www.yedirenkhaber.com.