Thursday, 10 September 2015

Didea fasciata - new for valley @ Garnwen

Seen one before in 2007 but didn't have a camera so I scrubbed that record because I didn't at the time confirm the yellow halteres [remains of the diptera hind-wings (they used to have 4 wings but now evolved into only two) which now acts as an organ of balance. There are three species of Didea but only Didea fasciata has yellow/pale halteres, while intermedia and alneti (last recorded in 1989) have a black haltere and neither has been recorded in Mid or South Wales. To identify a Didea you first have to confirm the loop in the wing of the R4+5 vein which is unusual amongst yellow and black hoverflies. Secondly, the oblique abdominal yellow markings gives Didea a very distinct and aggressive appearance. Another useful feature is that Didea has all black hind legs. Now we know it is a Didea we can check the halteres which in the case below can clearly be seen to be yellow/pale making it Didea fasciata.

                                                                          Haltere can be seen where the wings meet the abdomen
                                                           Aggressive looking species due to the yellow abdomen markings
                                                                    Another view of the haltere and also the all black hind legs