The aquatic shrew, a mouse in the pond

It comes out at sunset, scurries along the banks wriggling its long snout, dives into the pond to fish for small larvae. Discreet, the Crossope passes unnoticed.

The shrews, a large family

If we know the common shrew, small but great ally of the gardener, its semi-aquatic cousin, the Crossope, remains unknown. Frequent host of rivers, watercress beds, ponds and ditches, Neomys fodiens belongs to the same family, the Soricidae. It shows the same pointed, mobile snout, with long whiskers; its coat is rather grayish to black, with a well marked white belly. Of beautiful size, it measures up to 10 cm, without forgetting the tail, that is 8 cm more! This makes it the largest of the dozen shrews present in France.

An insatiable insectivore

The aquatic shrew comes out at sunset and is active all night long, looking for preys, mainly small invertebrates. On the menu: underwater, aquatic insect larvae, crustaceans, fry; on land, beetles, snails, worms, and even amphibians and small mammals. If its sight is weak, its sense of smell and hearing are excellent. Reinforced by mobile vibrissae, real underwater detectors. Its preys thus located, it seizes them with its small red and pointed teeth, poisons them by the toxic juices of its salivary glands. This is an efficient strategy, allowing this small mammal with high energy expenditure to be fed in abundance.

An accomplished swimmer

Water is its element, the aquatic shrew never goes too far from it. If it trots on the banks, it regularly dives with ease, swims between two waters, circulates on the bottom, goes up and floats like a cork.

It is nicknamed the "frame shrew". Its hind feet are lined with stiff hairs, reinforcing its support. Its tail is also equipped with two rows of the same hairs, and plays a powerful propelling role. Its coat is perfectly water repellent, and to complete the equipment, its auditory holes are obturable. An accomplished swimmer that will dig its burrow on the banks to house its young.

Many young

From April onwards, Crossopes are concerned about their offspring. Males and females meet each other, sometimes a little harshly. Through a small hole of 2 cm in diameter, the female will enter her carefully dug burrow. She will line it with plants rolled into a ball to accommodate 6 young on average. Her gestation will have lasted 2 weeks, 3 at the most. The reproduction will take place until September, the peak of the births being in May-June. The young will become adults after a few months and will reproduce in general the second year.

They will live at best 2 years. Mortality in the aquatic shrew is important, in the young as well as in the adults, especially during the breeding season.

Light traces

Discreet, nocturnal or crepuscular, the Crossope is difficult to see. Minute traces let us guess its passage. The fine and humid mud of the banks will be marked with light prints, with five fingers, without webbing. The posterior foot will measure hardly 1 to 1,5 cm, the anterior one will be even smaller. The droppings are almost invisible: 5 mm long, for 2 mm of diameter. Tiny droppings can be seen... Occasionally some remains of meals are observed, shells of snails, cases of caddisfly larvae, or better a larder supplied with preys half consumed. Other indication of presence, small acute nocturnal cries...

Small discreet mammal, the aquatic shrew plays an essential role in the aquatic ecosystems. But the degradation of its habitats is beginning to impact its populations, on the IUCN lists it is classified as a species of minor concern on the whole French territory, but in some departments the species is becoming almost threatened, vulnerable, even endangered.

The dragonfly, a useful insect in the garden

The dragonfly is an insect easily identifiable because of its large size, its translucent wings and its large faceted eyes. A carnivorous predator, the dragonfly is a useful insect in the garden.

The dragonfly is an animal that enjoys a good reputation among gardeners, and rightly so! This animal is indeed a formidable predator both when it is a larva and as an adult. Insect of the order Odonata, the dragonfly can be either of the suborder Zygoptera or of the suborder Anisoptera. The difference between the two suborders lies mainly in the shape of the eyes and the posture of the wings at rest (folded above the body in the zygoptera, or horizontal in the anisoptera).

Whatever the sub-order, the dragonfly is easily recognized by its large size (up to 110 mm wingspan). In adulthood, it has an elongated body with two pairs of wings generally transparent. It always lives near water (river, pond, basin...) for two essential reasons.

The first is that it lays its eggs in an aquatic environment. The second is that water attracts insects in number and it is thus there that it finds the best hunting ground. She enjoys flies and mosquitoes, which she hunts in full flight using a particularly well-honed technique. Its large faceted eyes allow it to count on a very piercing sight. The dragonfly in full hunting can easily make of the hover before melting on its prey. Fertilization in dragonflies is indirect.

The male will inject his spermatozoa in a special bag located on the abdomen of the female. The spermatozoa are thus stored without being fertilized. Fertilization is orchestrated by the female at the most opportune moment, generally during the month of May. Depending on the species, the female can lay up to 600 eggs. The eggs are deposited in the water where they will hatch releasing a prolarva. This one will know several stages of transformation.

The successive moults can last several months to several years depending on the species. During all its stay in water, the larva is a voracious predator. It eats in priority mud worms. The ultimate transformation is carried out out of water.

Unlike the butterfly, the larva does not go through a chrysalis stage. The passage between the stage of larva and that of the dragonfly corresponds to a final moult (known as imaginal moult).

The green frog, an attraction around the pond

The green frog or edible frog (Rana esculenta) is an amphibian that results from the hybridization between the Lessona frog (Rana lessonae) and the laughing frog (Rana ridibundus).

Of the Ranidae family, the green frog is green-brown and measures a good ten centimeters when adult. It populates our ponds, lakes, ponds and streams rich in vegetation that provides shelter. Its main predators are herons, pikes and snakes.

It comes out of its hibernation in March and resumes its place at the water's edge or on the water lilies. It is in summer, day and night, that we hear them the most. The males emit their songs especially at the end of the day or during the night to attract the females which will lay after the freshness of the gelatinous clusters composed of several thousands of eggs in the middle of the plants. After a few days, the tadpoles will appear and will remain in the water until the following spring when they will metamorphose into green frogs.

The green frog is a real attraction around the pond. Essentially an insectivore, it captures insects by leaping over 30 centimeters. It also feeds on earthworms, snails and slugs, and even other amphibians.

In November, with the return of the cold, the green frog will settle down to hibernate either in the mud or in a small gallery dug in the ground.

How to encourage the installation of frogs?

If your pond is colonized by frogs, the summers will be noisy! But what a show around the water. Children and adults alike will be delighted to watch them snatch up passing insects.

To help them settle in

• Install large rocks around your pond that will provide shelter for the winter but will also encourage the development of insects that will appreciate these shady and humid spots.
• Install a lot of vegetation on the edges of the pond.
• Install many flowers (lavender, perennial geranium, ...) that will bloom in a spread out manner from March to November. The flowers will attract foraging insects like bumblebees, bees and butterflies.
• Also install plenty of water plants to make them feel safe if the frogs need to hide from a predator.
• In winter, if you must handle the rocks, do so carefully, a toad or frog may be underneath.

The frog is protected

The handling of the animal is safe for humans. On the other hand all amphibians and reptiles are strictly protected, as well as their biotopes. The taking of samples in the wild is forbidden.

The great snail, a majestic snail in the pond

Of remarkable size, its elegant shell rolled up into a long point, the great snail crisscrosses the ponds with its quiet glide.

An aquatic snail

The great snail, Limnaea stagnalis, is a snail, with lungs, installed in quiet waters, with slow or non-existent currents. Imposing gastropod, its size can reach 5 to 6 cm, it remains elegant with its lengthened shell with the many spires. Accustomed to ponds, it is found throughout Europe, in the Northern hemisphere, Asia and America, alongside other limneas, all of the family Lymnaeidae.

A siphon to breathe oxygen from the air

If it lives in water, the Great Limnea cannot breathe oxygen. Its lungs need air. The attentive observer will have to wait long moments to see it finally going back to the surface, deploying a siphon, piercing the surface of the water and capturing the air necessary for long immersions. Immersions all the more long as the water will be well oxygenated, the gas exchanges taking place then also by the skin.

Its house on the back

Classic snail, the big Limnée carries its house. A "coat" on its back secretes a calcareous formation, of only one part it manufactures a twisted shell. In which she shelters her soft mollusc body, in case of predation and in times of drought. If its waiting in its shell must be prolonged, it will close the "door" using dried mucus, burying itself if possible in the mud.

A quiet path

On its muscular oval foot, the large Limnea surveys the bottom of the pond, its reliefs, slips from plants to plants. One can see it floating sometimes, between two waters, in ascending or descending movement. At the surface of the pond, between water and air, it is placed upside down and its mucus-covered foot is flush with the air. She glides slowly, feeding on the biofilm formed on the stagnant water.

She grazes, grazes

The great dabbler spends long moments grazing. Its two long triangular tentacles are surmounted by two eyes, below which is placed the mouth. In this mouth is the radula, which could resemble a rasping tongue, covered with asperities that allow it to scrape decomposing plants, to graze the aquatic bottom, to tear some particles from occasional decomposing corpses.

Males and females, aquatic meetings

The great snail, like many snails, is hermaphroditic, the same individual carrying, in a complex anatomy, the male and female sexes. After cross fertilization, sometimes with several individuals, the eggs are laid on the walls or on the plants in extremely adhesive elongated socks. After three weeks, more or less according to the temperature, the eggs hatch and come out tiny Limnea whose body and shell will grow in a few months.

Majestic, slow-moving, the great snail is one of the easiest to observe in the pond. Not very demanding, an abundant vegetation, a calm water and detritus will be enough to welcome it.

The gambusia, against mosquitoes

The Gambusia, from its small name Gambusia affinis, is a small freshwater fish native to the United States that likes to live in schools. It has been successfully introduced in several French regions, including the marshes of the Camargue and certain rivers in the southwest, in order to combat the proliferation of mosquitoes.

Presentation

The gambusia is part of the order Cyprinodontiformes. It is a cousin of the guppies that we commonly find in our aquariums, however its colors are less bright: they vary from gray to light green.

The head is large but ends in a point at the level of the mouth which is provided with many teeth.

The dorsal fin of the gambusia is positioned at the back of the body and is not very developed whereas the caudal fin is larger in the shape of a rounded fan. The ventral fin is located at the base of the tail, it is short and rounded in the female and is transformed in the male into a long pointed organ, the gonopod intended for the copulation.  The male is smaller than the female (3,5 cm against 6,5 cm for the female). In addition to their size, they are differentiated by the black spot that the female has on her abdomen.

Habitat and feeding

Native of the hot zones of the United States, the gambusia has incredible faculties of adaptation, what was worth to him to be introduced from share the world to fight against the plague of the malaria and other diseases carried by the mosquitos. Its preferred waters are fresh but it is not uncommon to find it in brackish waters or in saturated waters with very low oxygen content.

The gambusia is found in large numbers in Mexico, Cuba, Jamaica and Nicaragua. It can be described as robust and combative: it must often be isolated when it lives in an aquarium because it tends to attack the fins of other fish, it can even eat its own young.

Gambusia feed on mosquito larvae, bloodworms, water fleas or even tadpoles.

Life cycle

The reproduction period of the gambusir is from April to October. Males insert their gonopod into the genital opening of females and fertilize the eggs.

The fertilized females lay fry over a long period of time with intervals of a few weeks between each spawning.

The fry, less than 10 mm in size, are just born and disperse into the vegetation where they continue to develop until they reach sexual maturity six months later.

The life span of the Gambusia is approximately two years.

The craspedote, a freshwater jellyfish

They scare, fascinate: jellyfish populate the seas and oceans, and leave neither holidaymakers nor naturalists unmoved. And when we meet a small species in our lakes, ponds, canals, after a moment of surprise, we can only go to discover Craspedacusta sowerby, present in freshwater of all continents.

A small jellyfish in our water bodies

In 1880, London scientists discovered a jellyfish in a pond of exotic plants. Translucent, it is clearly visible to the naked eye with its 2 cm diameter. Named Craspedacusta sowerbyi, or freshwater Craspedote, it belongs to the Cnidaria, a cousin of the jellyfish of the seas and oceans, but also of anemones and corals. It is the only freshwater jellyfish that meets in its class of Hydrozoans only Hydras, polyps always fixed.

Since its first description in London, the Craspedote has been observed on all continents, in 1929 in the Garonne pond and then in all the rivers of France.

Fragile and elegant

The encounter is surprising: bending over the waters of a lake, a canal, an old gravel pit, or even a pond, one sees small translucent, parachute-shaped organisms the size of a 2 euro coin floating. The freshwater Craspedote is a typical Hydrozoan: its umbrella is lined with more or less long tentacles, up to 400, a velum closes the parachute on its lower face. Under the umbel, crossing the velum, a tube, the manubrium, springs out, equipped with an external orifice and connected to 4 radial channels in intern. All the anatomy of the medusa is visible by transparency.

It floats in the middle of its preys

The freshwater Craspedote can move by vigorous contractions of its umbrella, but lets itself float according to the movements of the water, among the zooplankton. It is thus within reach of its preys. Copepods, daphnids, all the small animals of the plankton will be captured by its tentacles, carried to the opening of the manubrium, the mouth, to be swallowed. Once the digestion is finished, the waste will be rejected by the same orifice, serving as anus this time.

In Craspedotes the tentacles are provided with cnidocytes, stinging cells provided with harpoons with paralyzing effects. Only on small preys, the man does not seem to have to worry about its presence, its epidermis cannot be crossed.

It appears and disappears suddenly

The Freshwater Craspedote can go unnoticed one year, as well as proliferate in abundant populations the following year. Then disappear again. Before being a floating jellyfish that can be observed with the naked eye, it takes the form of a tiny polyp of a few millimeters attached to the bottom, to vegetation, to rocks. Its small tentacles allow it to feed on animal micoplankton. This polyp will reproduce by asexual way, by budding, release of crawling "larvae" moving and forming a new polyp, and production of medusoid buds. Some will become medusas leading a sexual reproduction. The fertilized eggs will pass through the planula stage, a small floating ciliated larva that will settle and become a polyp.

Present on all continents and therefore considered as an invasive species, the freshwater Craspedote would not represent a threat to ecosystems. Its feeding in zooplankton remains limited, its presence remains discreet. The impact of climate change on the evolution of the populations of this species may however modify the current data in the coming years.