The aquatic insects are a group of organisms of the Arthropoda Phyllum and the class Insecta which have morphological adaptations to live in aquatic environments. These adaptations can be to be present in the aquatic environment only in the first stages of life or throughout its life cycle.
Insects are the most diverse animal group in terms of number of species, morphological, ethological (behavioral) and physiological variety. More than 1 million described species are known capable of consuming a great variety of foods and being part of the food of an incredible variety of organisms.
The enormous diversity of these animals has led them to colonize almost all environments known to man. Most of these can fly, others, although they have wings, are adapted to live on the ground or on other substrates, and some present adaptations such that they allow them to swim, hunt and develop on and under the water.
Insects are arthropods, that is, they are triblastic organisms (they have three embryonic layers: ectoderm, mesoderm and endoderm), coelomates, protostomes (during development the blastopore develops the mouth), with segmented bodies and with a mainly chitinous exoskeleton.
They present a varied differentiation of the body (tagmosis). They have sclerites, that is, hardened plates that are part of the exoskeleton.
It presents metamorphosis, which depending on the group can be complete (holometabola) or incomplete (hemimetabola). Some species may have direct development, that is, the individual does not go through larval stages and when the egg hatches, the juvenile individual will have some similarity to an adult organism.
In order to grow, arthropods need to shed the old shell (exoskeleton) and replace it with a new, larger one. This process of shell change is called ecdysis or molting.
These are general characteristics of arthropods, however, insects have other characteristics that separate them from the rest of arthropods, and aquatic ones have other than the differences from other terrestrial forms.
In general, insects present a tagmosis of the head, thorax and abdomen. On the head they have a pair of antennae, compound eyes (some may have ocelli) and developed oral structures (1 pair of mandibles, 1 pair of maxillae and 1 pair of palps).
They are mainly winged organisms. They have three pairs of legs (6 in total). Most are terrestrial and some forms are aquatic or at least some part of their development is carried out in an aquatic environment.
Adaptations of insects to the aquatic environment
Evolutionarily, it is thought that the insects went from the terrestrial to the aquatic environment. These organisms (about 30 thousand species) found in freshwater ponds, rivers and lakes a potentially exploitable environment and practically without competition, a situation that did not occur in the marine environment.
In this last environment they had to compete with groups such as crustaceans . That is why they have not thrived at sea. Now, the adaptations that allowed insects to be successful in aquatic environments are the following:
– Legs modified for swimming (rowing forms for example).
– Mushrooms (hair-like structures) swimming on the legs.
– Flattened abdomen that facilitates swimming.
– Legs and / or abdomen modified to hold on to substrates.
– Suction cups that allow them to be attached to the substrate.
– Hydrodynamic body shapes.
– Use of silk for the construction of underwater shelters.
– Complex life cycles, where at least the larval stage develops in water.
– Some species have hemoglobin in the circulatory system (hemolymph) that allows it to store oxygen.
– Some have highly developed respiratory structures such as gills.
– Certain organisms use air bubbles to dive and others have structures similar to a snorkel.
The insects belong to the phyllum Athropoda, subphyllum Hexapoda (known as six legs), and class Insecta. The class is divided into two subclasses; Apterygota (wingless insects) and Pterygota (winged insects). Of this large taxonomic group, more than 1 million species have been described and it is thought that many species still need to be described.
The two subclasses of insects are currently composed of 20 orders, of which 13 have species that inhabit partially or permanently in aquatic environments. These orders are:
– Coleoptera (beetles).
– Hemiptera (bed bugs, aphids and cicadas).
– Odonata (dragonfly in English, damselflies, dragonflies).
– Ephemeroptera (ephemeral, also called damselflies).
– Plecoptera (stone flies or stone flies).
– Megaloptera (, alder osca, dobson fly).
– Trychoptera (caddisflies in English)
– Diptera (flies, horseflies, mosquitoes)
– Neuroptera (lacewing, lacewing)
– Hymenoptera (ants, bees, bumblebees, cigarillos, ants, bachacos, wasps)
– Lepidoptera (butterflies, moths)
– Mecoptera (scorpion flies)
– Blattodea (cockroaches)
Aquatic insects are distributed mainly in fresh water bodies such as ponds, lakes, rivers, small temporary ponds and phytotelmatas (vegetable water containers, such as tree trunks and leaves); very few have been successful in marine and estuarine environments.
They are common in waters rich in oxygen, mainly free of contaminants. They tolerate living in waters with different pH variations. They can live at temperatures below 40 ° Celsius
Some live in environments with currents such as streams, streams or rivers, and others in stagnant or slow moving waters. There are pelagic, benthic and neustonic species:
Pelagic species inhabit the water column as planktonic organisms (in the case of the larvae of some Diptera) or nektonic organisms, that is, they are able to actively swim and overcome currents.
They are organisms that are associated with the fund. Benthic aquatic insects live associated with muddy, rocky and sandy bottoms. They are often seen digging through the substrate, taking refuge under rocks, or inhabiting and feeding on the stems and roots of aquatic plants.
They are organisms that make up the pleuston. The necton is divided into hiponeuston, living in the aqueous interface, and epineuston, living in the air interface, i.e. in the water film. Some families of Hemiptera (bed bugs) walk on the surface of the water (skating insects).
While some ecologists consider them terrestrial or semi-aquatic, other researchers consider them aquatic insects.
All animals require an efficient respiratory system, which allows them to carry out the oxygen-carbon dioxide gas exchange. In insects this function is fulfilled by the tracheal system.
The tracheal system is made up of an extensive network of thin and highly branched tubes or tubules, which are distributed throughout the body of the insect.
The tracheal trunks are another structure of this system that is connected to the outside through the spiracles (external orifices generally paired and that function as an opening and closing valve), which is where the air enters and distributes it to the whole body through the tubule network.
The tracheal system is characteristic of terrestrial insects, however in aquatic insects there are an interesting variety of structures that serve these organisms to carry out gas exchange:
Some insect larvae can obtain oxygen from water by diffusing it through the thin walls of the body.
The nymphs of certain Plecoptera present a system of tracheal gills as expansions of the body wall. In Odonata nymphs (damselflies or dragonflies) these gills are found in the rectum and are called rectal gills.
Most aquatic insects breathe atmospheric air, so they must come up to breathe every so often.
There are species that have appendages that serve as snorkels, others have incorporated respiratory pigments in their circulatory system that allow them to endure more under water, and some manage to submerge using air bubbles like scuba divers.
Like terrestrial insects, aquatic insects feed herbivorous (plants and vegetables) and carnivorous (other animals).
From this and from the ecological point of view, the types of feeding are very varied, so it is worth saying that aquatic insects are organisms that have representatives that feed on plankton (planctophages), detritus (detritivores), carnivores and parasites.
Examples of species
Diptera insect known as mosquito or mosquito, its eggs and larvae have an aquatic phase. They are a species with high medical importance, since they are vectors of diseases such as Zika, yellow fever, dengue, among others.
It is a species of beetle in the Curculionidae family. Their larvae live associated with aquatic grasses from which they obtain oxygen and food. As adults they are pests of rice fields.
It is known that the adult organisms of this species can be submerged for up to 50 hours, thanks to the fact that they take advantage of the air contained in the folds of their wings, through the spiracles of the abdomen.
It is a water cockroach of the order Hemiptera. Their eggs are laid on the surface of the water or on plants and / or objects. They are called giant aquatic insects. They are important predators of the freshwater bodies of Southeast Asia and Australia. It is considered a delicacy of Asian cuisine.
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