Invertebrates are small animals, present in every environment in very high numbers.
They are numerous in meadows and woods, surface waters and groundwaters. Many of them live in the soil where it is estimated there are several millions of individuals per square meter, most of which are microscopic in size.
In resurgences the presence of aquatic habitats and wetlands, of woods and natural meadow, of fresh and clean waters favor the presence of many groups of invertebrates such as snails, earthworms, leeches, spiders, crustaceans and more numerous of all, the insects with dragonflies, grasshoppers, butterflies, beetles, mosquitoes, flies, wasps and bees.
Among the thousands of species of invertebrates in resurgences there are 4 species of Community interest included in the Habitats Directive, which are: Vertigo angustior, a wetlands snail, the stag beetle (Lucanus cervus), a beetle found in mature forests of oak, the butterfly Coenonympha oedippus, related to wetlands and rare throughout Europe, the freshwater crayfish (Austropotamobius pallipes fulcisianus).
In the resurgences waters live various groups of invertebrates, the best known are the molluscs, crustaceans and insects. Aquatic invertebrates feed in several ways: the detritivores (crustaceans and some insect species) feed on plant debris or dead animals; herbivores (crustaceans, insects, aquatic snails) feed on algae or aquatic plants or abrade the patina of algae from stones or by vegetation (aquatic snails as Planorbarius corneus), carnivores (leeches, crustaceans, insects) feed on other invertebrates, or sometimes even fish fry and tadpoles of amphibians.
The largest invertebrate is the crayfish, other crustaceans of resurgences aresmaller in size from few inches (such as species of Gammarus and Asellus) to few millimeters.
Among insects deserves mention some groups that spend most of their lives, usually as larvae, in water and the second (adult) rather than land. These include the mayfly, the caddisflies, dragonflies and flies.
The female insects lay their eggs on the water surface or on vegetation. The development of larvae in the water can last for several years. Adults are flightless and usually live from few days (ephemeroptera) to several months (dragonflies). Adults of some species do not feed at all and die soon after reproduction. In the waters you can see some adult beetles (like the big ditisco, Dytiscus marginalis), which are carnivores and fast swimmers, but also good flyers. Related to aquatic environments there are also some Heteroptera, including swimmers carnivores, such as water scorpion (Nepa cinerea) or those more easily observed, walking or skating on the water surface, as Gerris lacustris.
Some species of aquatic invertebrates are present only in clean and well oxygenated waters and their presence or absence in a given environment is considered an indicator of environmental conditions. These species are considered bioindicators.
In the narrow strip of groundwaters emergence have been found stigobi invertebrates. This term refers to the animals that live only in groundwaters, in the perennial dark, usually in caves or underground. Stigobi invertebrates have no eyes and are white because without body pigments. These are mainly crustaceans of different sizes (up to 2 cm).
Some species found in resurgences are endemic, ie exclusive of northeastern Italy. Their presence indicates that Friuli groundwaters, in spite of intense agricultural activities, have retained a good quality.
In many resurgences of the Po Valley stigobie species have instead disappeared.
In terrestrial environments, invertebrates that can be observed most frequently are molluscs (snails), worms, spiders, crustaceans and insects (dragonflies, grasshoppers, butterflies, beetles, mosquitoes and flies, wasps and bees).
The snails live mostly in the wettest places like the edges of woods, near ditches, under stones, in litter, in wet meadows and peat bogs. The species of Community interest Vertigo angustrios live near the water, on plants or in the mud of the shore. It is considered a good indicator of environmental quality.
Terrestrial invertebrates are undoubtedly the most numerous insects and are especially interesting ones related to wetlands. In wet meadows and peat bog edges can live grasshoppers and rare butterflies: Chrysochraon dispar giganteus which was previously only known from the brackish areasof the lagoon was found here. It is a very rare grasshopper and it is endangered of extinction throughout all Europe. In Italy it is present only in the north-east. Its discovery in resurgences confirms the high naturalistic value and the good state of conservation of the area.
Another rare grasshopper found in this area is Micropodisma salamander. It is present in the north-east part of Italy only. It is a species widespread in the mountains and adapted to low temperatures. In plain is only found in cooler environments, such as resurgences.
Among the more than 150 species of butterflies recorded in resurgences area, several are related to wetlands because their larvae feed on plants found only in these environments. Some butterflies are considered endangered due to loss of wetlands in much of Europe and Italy, as the Coenonympha oedippus, which is linked to wet meadows near water outcrops, an environment very rare now. Another endangered specie, the moth Elophila rivulalis lives here because the larva found its habitat in small streams with slow moving water.
The beetles are found mostly in the woods; here were also found bio-indicator species of wet areas as Platysma (Melanius) rhaeticum, Phonias strenuus, Drypta dentata of carabidae family and Euaethetus laeviusculus, Myllaena masoni, Staphylinus erythropterus, Tachyporus transversalis of stafilinidae family, found in Italy in few stations only.
The most striking beetle is certainly the stag beetle (Lucanus cervus).