Butterfly of the Month - January 2024
The Bronze Flat (Netrocoryne repanda repanda) is of an almost shiny appearance when newly emerged from its pupa. The brown wing colour contrasts with cream to yellowish as well as dark brown spots or markings which may vary slightly. The male butterfly reaches a wingspan of 39mm, the female of 41mm. Upper and underside are very similar.
Netrocoryne repanda belongs to the Hesperiidae family. At first glance it may be confused with Chaetocneme denitza (Ornate Dusk-flat) and to a lesser extent with C. beata (Eastern Dusk-flat). Wing patterns are somewhat similar, but Chaetocneme spp are slightly larger, have red eyes, whereas our Bronze Flat’s are brown. It can also be distinguished from Chaetocneme spp by the outer forewing margins which are scalloped unlike the evenly rounded ones of the Dusk-flat butterflies, and by hindwings which, in comparison, present themselves as a more square shape.
The butterfly starts its life cycle with a dome shaped ribbed egg of brown colour. It is just over 1mm in diameter and less than that in height. It is laid singly on the upper leaf side of the larval host plant. Unlike the larvae of most other butterflies this one doesn’t eat the egg shell once hatched.
The larva develops from a plain coloured early instar to a more elaborate striated pattern exhibiting a greyish green and later a grey colour, flanked by yellow, and with some black spots. The larva provides for its own protection by creating a shelter. It partly cuts out a piece of the leaf, folds it over and attaches it to the upper surface with a fine strand of silk. This shelter grows with instar sizes. Six instar stages are completed (most other butterflies undergo five). Feeding occurs at night time while the larva rests in the shelter during the day. Pupation happens inside the same shelter. The dark purplish-brown pupa is secured with silk thread and girdle within it.
The butterfly is endemic to Australia. Two subspecies exist. N. repanda expansa only occurs in north-eastern Qld, whereas the distribution of N. repanda repanda is more expansive. It can be found between the Whitsunday region and Victoria, and has been recorded in Central Queensland at the Carnarvon Ranges. The butterfly uses dry eucalypt forests as well as rainforest and may exists in low lying coastal areas as well as at higher elevations. The adult males are known for their hilltopping behaviour. They perch with open wings.
Netrocoryne repanda repanda feeds on a large variety of larval host from different plant families. Among them are Cryptocarya spp (Laurels), Elaeocarpus reticulatus (Blueberry Ash), Neolitsea dealbata (White Bolly Gum), Lophostemon confertus (Brush Box), Scolopia braunii (Flintwood), Notelaea longifolia (Long-leaved Olive), and - of course - Brachychiton populneus (Kurrajong).
Images:
GW – Geoff Walker; RF – Ross Field , CC BY-SA 3.0au; SH – Simon Hinkley, Museum Victoria, CC BY-SA 3.0au
