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Dragonfly extendable labium – The mask

Dragonfly mask

A common feature of the nymphs of order Odonata is the extendable lower lip (the mask), which is in idle state composed under the head. The mask consists of two connected parts. It ends with thorns, which are used to grab the prey. Aeshnidae nymphs have very well developed eyesight, allowing them to chase moving animals. When hunting the mask is extended by contraction of muscles and body fluids against the prey, thereby greatly increasing the reach. The speed of such a thrust can be up to 25 milliseconds and the nymph is able to vanquish a prey larger than itself.

Dragonfly nymphs - mealtime

 

Darner dragonfly nymph (Aeshnidae), feeding on mayfly nymph

Odonata – Libellulidae and Cordulegastridae nymphs

The way of life and stealthy movements of the nymphs of dragonflies sharply contrast with the aerobatic flight of adults. Partially buried in sediments or hidden in aquatic vegetation patiently lurk for their prey. Covered with a layer of algae and aquatic sediments are in idle state almost invisible. Extendable spoon-shaped mask is a perfect tool for hunting small aquatic animals. Parts of the mask during extension spread out and grab the prey, which is then tightened back and crushed by strong mandibles.

Spiketail dragonfly nymph (Cordulegastridae)

Cordulegastridae is the family of dragonflies with typical bottom-living nymphs. Using their legs and side to side movements are able to burrow themselves quickly into the sand or mud. All Anisopteran nymphs breathe underwater using gills inside the abdomen. The water is pumped in and out of the rectum. They use sit and wait hunting strategy and can stay hidden while reaching oxygenated water only with the apex of abdomen above the sand.

 

Páskovcovití patří mezi vážky, jejichž larvy obývají písčité nebo bahnité dno, kde se pomocí nohou a pohybů těla mohou rychle ukrýt. Všechny larvy z podřádu Anisoptera (různokřídlice) dýchají pomocí tracheálních žaber rozvětvených ve střevech. Kyslík se do nich dostává nasáváním a vypuzováním vody konečníkem. Většinu života tráví nehybně a vyčkávají, až se kořist přiblíží na dosah.

Emerald dragonfly emerging

Dragonfly hatching

There are three stages of the dragonfly life cycle, the egg, the nymph, and the adult dragonfly. Most of the life cycle of a dragonfly is lived out in the nymph stage. Once the nymph is fully grown, it will complete the metamorphosis into a dragonfly by crawling out of the water up the stem of a plant. Firmly adhere to the shore or stems of plants and emerge in the adult. The skin that the nymph left behind is called the exuvia and it can be found still stuck to the stem for a long time after the dragonfly has left it. Adult dragonflies only live about two months while hunting for food, looking for a mate and laying the eggs and the life cycle of the dragonfly begins all over again.

Mayfly nymphs, (Ephemeroptera)

Lifespan of adult mayflies ranged from several hours to two days. Depends on the species and ambient temperature plays a role too. The adult lifespan is so short there is no need for the insect to feed and therefore the adult does not possess functional mouthparts and digestive tract. Consequently, the majority of their life is lived out in the nymph stage and serve as important food source for fish. The way of life of the nymphs is highly diverse. They eat mostly plant food, especially algae and detritus – small particles of organic matter in various stages of decomposition. Most of the nymphs of mayflies have three caudal filaments, gills on the sides of the abdomen and each leg equipped with the single tarsal claw. Nymphs are adapted to specific aquatic environment and thus we can distinguish several basic types according to body shape.

Order: Ephemeroptera (Mayflies), Family: Heptageniidae (Flathead Mayflies, clingers)

Nymphs with a substantially flattened body, legs spread to the sides and eyes on the back of the head are perfectly adapted to live under the rocks. (This is known behavior of fish turning stones to find the nymphs.) Due to the shape of the body and strong legs ending in claws are able to maintain and move in fast flowing waters, when searching for food. Heptageniid nymphs are clinging scrapers that feed on algae attached to the surface of stones, wood and aquatic plants.

 

Order: Ephemeroptera (Mayflies), Family: Baetidae (Minnow Mayflies, swimmers)

Nymphs of tightening streamlined body shape are very skilled swimmers, hence the name Minnow mayflies. They have a rounded head bearing a pair of long antennae, rapidly oscillating plate-like gills on the sides of the abdomen and three long hairy filaments. By synchronizing the movements of these body parts can quickly escape the predators. They feed on plant matter and organic debris.

 

Order: Ephemeroptera (Mayflies), Family: Ephemeridae (Common burrowing Mayflies)

Burrowing nymphs with a long cylindrical body are found in the soft silt or sand at the bottom. Upturned mandibular tusks near the mouthparts and strong front legs help when burrowing. Ephemerid nymphs create a current of water through the U-shaped burrows by moving their branched gills. This current brings oxygenated water and detritus which they feed on.

Mayfly emerging

Mayfly hatching

 

When is the mayfly nymph fully grows, rises to the surface. As the one of its first tough tests awaiting is to overcome the surface tension of water. In the moment of contact with air nymphal cuticle bursts and for straightening the wings helps in swimming as a raft. In this case, it is not a mature adult, but a winged nymphal stage. It usually takes only a few minutes, after which the so-called subimago molts again and takes off as an adult, imago. The nymphs of some species of mayflies are evolving for several years to gave the basis for future generations within a very short time. In the same way as we would like to settle up all the adult matters in the last month of our human life.

Case-building Caddisfly larvae

Trichoptera

Caddisfly larvae live on the bottom of both still and running waters. Cases, which they drag along with them, protect a soft abdomen. Different materials are used for the construction of protective cases. The used construction material is usually characteristic for specific species. It can be sand of different grain size, needles, stalks of plants, but also the shells of aquatic snails – to the misfortune of their opportune residents.

Caddisfly larvae - underwater architects

 

 

Net-spinning Caddisfly larvae

Trichoptera

Caddisfly larvae of some species build their homes tightly fastened to the stones. This shelter is often equipped with a trapping net into which larvae capture organic debris and small animals drifting in stream. The same as in case of the larvae making portable shelters, these structures are connected by silk fibers excreted from salivary glands near the mandibles of the larvae.

Water scorpion – Nepa cinerea

Water scorpion (Nepa cinerea)

Near the banks and in the sediments of still water lives one of the largest water scorpions – Nepa cinerea. It is not an efficient swimmer. Mostly walking slowly along the bottom or waiting for a prey. Its hunting tactic is imitating a parts of aquatic vegetation. When the unsuspecting victim occurs nearby, quickly captivates it by the front pair of raptorial legs, in the same way like mantis. It feeds on small aquatic animals and insects stuck on the water surface.

 

Water scorpions (Ranatra linearis, Nepa cinerea)

A common feature of Heteroptera is indented stinging organ, which is used to suck their prey.

The front pair of raptorial legs is used to grab and immobilize the prey. From the grip resembling a closing mechanism of the clasp-knife is very difficult to escape.

Since Water scorpion breathes atmospheric oxygen, has some time to climb to the surface. Pops out of the water only a breathing tube on the end of the abdomen and draws the new air supply.





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