Belonging to the predaceous Dytiscidae family of diving beetles, the Acilius duvergeri is another creature, this time an insect, that is being listed as vulnerable in several countries - including Algeria and Italy, Morocco, Portugal and Spain - before it has even been given a common name.
Such is this poor creature's plight, that the English speaking world seems to know very little about it - it took several hours to unearth the details given here in a Spanish/ Portuguese publication. As it is, translation revealed quite a few interesting bits of information concerning the Acilius duvergeri.
Acilius duvergeri is an oval, slightly flattened mid-sized diving beetle reaching an overall length of approximately half an inch (12.5 to 13 mm). The body of the Acilius duvergeri is mid to dark brown, and the head is yellowish, with a black trailing edge and a characteristic V-shaped black stain.
The pronotum (surface of the first thorax segment, or prothorax) is also yellowish, and is marked by a pair of black traverse bands, which may be wavy and are connected by a more or less visible line in the middle. The pronotal (adj. of pronotum) punctuation is spaced and very fine, while the also yellowish elytra (wing case, the chitinous or leathery forewing covering the membranous, thin hind-wings used for flying) features joined black spots.
The thorax of the Acilius duvergeri is black, with yellowish sub-tones, while the abdomen shows a varied yellowish to brown coloration. Acilius duvergeri' legs equally show yellowish tones, with dark-brown metatibias and metatarsals.
The fine, spaced punctuation of the pronotum, the small size and narrow body shape of the Acilius duvergeri, along with the not very clearly defined suction cups in the males and the lack of defined grooves on the elytra of the females, clearly distinguishes this species from others in the genus. This is accentuated by detailed studies of the Acilius duvergeri's larvae.
Biology and Ecology
It has been suggested (Dettner, 1981) that the larvae of the Acilius duvergeri develops in temporary, shallow stagnant bodies of water during spring and into early summer. As these temporary bodies dry up, the adults migrate into the deeper waters of permanent ponds or lakes.
Both the larvae and the adult Acilius duvergeri are strictly aquatic predators, although the adult may also scavenge. Like other species found in the genus, the Acilius duvergeri is a good swimmer and flier.
The Acilius duvergeri prefers fresh, not too bright or cold water containing an abundance of helophytes and macrophytes, such as, for example, Typha. It has been found in both temporary and permanent ponds, mainly in coastal areas, of south-west France - especially in the Landes region and Gironde; several coastal areas, such as the lower Alentejoto Coimbra and the Hueva coast, in Portugal.
Other areas where populations have been reported include inland areas of Spain (Zamorra, Leon, Palencia); between Rabat and Tangier in Morocco, and a couple of areas on the Italian island of Sicily. It is also believed to inhabit some areas of Algeria.
The habitat of the Acilius duvergeri is continually being reduced by expansion of urban activities, farming, and extraction/ diversion of water-sources for irrigation of farmland, which is gradually eliminating the natural flood plains. This, combined with agricultural accidents leading to organic and chemical substances to wash into ponds and lakes, reduces the aquatic diversity of the area and makes it difficult for both larvae and adults to find shelter and food.
It has been suggested that measures to guide and control both drainage of excess irrigation and extraction of water from flood plains, promotion of organic products in agriculture and restoration and protection of flood plains and coastal freshwater lagoons are necessary to assist the survival of this species.
Considering that the outstanding morphological differences of the Acilius duvergeri in comparison with other species of the same genus do suggest an extremely high phylogenetic uniqueness, reflecting the possibility of the Acilius duvergeri being an extraordinary, true relic, it is sad to see that at the moment, the species does not enjoy any form of legal protection.
Dettner, T. 1981. Erstnachweis von Acilius (Homoeolytrus) duvergeri Govt. (Col: Dytiscidae) für die italienische Fauna. Entomol. Z., 91 (18): 201-208