Posted by nick upton on 23-11-2010 20:40
#1
Can anyone identify these large wingless pond skaters in a tandem pair to genus/species. Could they be Aquarius najas?
4.6.2010 Corsican mountain stream at c 450m
Posted by atylotus on 25-11-2010 10:52
#2
Dear Nick
I hope you did collect the specimens !
According to Aukema & Rieger there are no (published) records of any species of Gerridae from Corsica, so it will be the first. To me it looks like an Aquarius species (wingless species with long first antennal segment), but definately not A. paludum. Unfortunately there are 3 species in the meditteranean area looking like A.najas i.e. A. najas, A. cinereus and A. ventralis.
They key out something like this.
1. Relatively short and robust species, greatest width more than 0.25x body length. Connexiva patterned with yellow spots. Males 8.4-12 mm, females 11.2-15.6 mm.....Aquarius ventralis
- Longer and more slender species, greatest width less than 0.25x body length. Connexiva at most with yellowish margins......2
2. Larger species, males 12-14.3 mm, females 15.3-17.8 mm. Dorsal side of body blackish....Aquarius najas
- Smaller species, male 8-10.9 mm, females 10.5-14.4 mm. Dorsal side of body usually greyish....Aquarius cinereus.
I do have A. najas and A. ventralis in my collection, but I do not have that many experience in identifying them just by looking at the photo.
Distribution:
A. ventralis: Turkey, Cyprus, Bulgaria and Greece
A. cinereus: France, Italy, Portugal, Spain, Northern Africa
A. najas: Europe, Northern Africa
Edited by atylotus on 25-11-2010 10:54
Posted by nick upton on 25-11-2010 23:08
#3
Many thanks for this very interesting response. No wonder I couldn't find any other photos or records of Gerridae in Corsica.
Sorry, no specimens. I only collect photos... There really were a lot of them, though. The site was a very clear, clean mountain stream.
From the size and shape, based on your key, I'd say they may have been A. najas, they were BIG But the colour was neither black not grey dorsally but quite sandy coloured. I've seen other photos claiming to be of A najas that look like this, though.
Seems specimens would be needed to be sure. They were on the Taravo river between Ajaccio and Propriano, near where the N196 crosses it.