2017 July 2

   Reminder:  From July 6 to July 22 (Jeremy Tatum writes) I shall be on holiday and very unlikely to be able to operate Invert Alert.  By all means save up a very few of your most interesting photographs for when I get back, especially of insects rarely photographed, but it would be nice if, upon my return, I did not have to process large numbers of photographs of our frequently-photographed insects.  Thank you all.

   Jeff Gaskin writes:  Yesterday, July 1, I was at Swan Lake and I found the following butterflies :  28 Lorquin’s Admirals, 11 Western Tiger Swallowtails, 10 Cabbage Whites, 2 Essex Skippers, and 1 Painted Lady.

  Gerry and Wendy Ansell write:  A visit to Cowichan Station on Saturday July 1, 2017, produced the following butterflies:

Margined Whites 6+

Red Admiral 2

Cabbage White 5

Western Tiger Swallowtail 4

Lorquin’s Admiral 2

Margined White Pieris marginalis (Lep.: Pieridae)  Wendy Ansell

Margined White Pieris marginalis (Lep.: Pieridae)  Wendy Ansell

Margined White Pieris marginalis (Lep.: Pieridae)  Wendy Ansell

   Jeremy Tatum writes:  I am very interested in this butterfly, so I hope viewers will excuse a few paragraphs of text.  I have once found a caterpillar, and once a chrysalis, of this species north of Cowichan Station.  Both were on Dame’s Rocket Hesperis matronalis, and were successfully reared on this plant.  However, I suspect the main foodplant is Watercress Nasturtium officinale.  Both of these plants grow abundantly there.  The first two photographs show a butterfly nectaring on Watercress. The third photograph shows one nectaring at Herb Robert Geranium robertianum, which is not a larval foodplant, but the adults frequently take nectar from these flowers.  [Added in press, just before posting:  The identity of the plant I have been calling Watercress Nasturtium officinale needs confirmation.  If a botanist can help, let us know.  Keep an eye on this site for what we eventually conclude.]

  Many of our Margined White butterflies are totally immaculate – pure white with no markings. There are no particular markings on the margins of the wings – the English name is just copied from the scientific name marginalis, which is merely a label, and not descriptive.  However, in some (such as the one in the third photograph) the veins on the underside of the wings are accentuated with grey.  I have seen specimens with veins more accentuated than this.  Also occasionally I have seen a pair of gray spots in the middle of the upperside of the forewings.

   I suspect (but am not 100 percent certain) that there is a sex difference, the females being more heavily marked than the males. I also suspect that the species is bivoltine, and the spring generation is more heavily marked than the summer generation.   Thus if you see a heavily-veined butterfly on the underside, with two grey spots on the forewing upperside it is likely to be a spring generation female.  A summer-generation male, on the other hand, is pure unsullied white.

  Finally (for now anyway!) from what I have been able to see, the caterpillar and chrysalis are indistinguishable from those of the European Green-veined White Pieris napi.  I believe that, depending on one’s concept of “species”, a case could be made for saying that the two are conspecific, and that Pieris napi is a Holarctic species with a wide range, and with a corresponding wide range in the variation of its maculation.  I have seen Green-veined Whites in Scotland that are very heavily marked, and one could be forgiven for doubting that they are the same species as our immaculate Margined White – until one has seen the very similar caterpillars and chrysalides.