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Two very rare butterflies spotted in Grasslands at Riddells Creek

posted 11 Jan 2011, 03:50 by Russell Best   [ updated 21 Mar 2011, 03:52 ]
Not one but two rare butterflies! Keep your eyes open for them.

While doing some survey work for the rare Purple Donkey-orchid population in Riddells Creek on Dec 16 2010, Russell Best photographed a 'Skipper' butterfly he hadn't seen before. It took his eye because when it landed a few metres away it was noticeably yellowish on the outside. Nothing was thought of it for a week or so (because skippers are often seen in Riddell). When it came to identifying it, based on the available info at hand (which was very good info), it didn't seem to obviously fit any picture of any species. The only ID that seemed to fit was the rare, and FFG-listed Yellow Ochre butterfly (Trapezites lutea lutea - pictured left) (FFG-listed means protected by law by Victoria's "Flora and Fauna Guarantee Act"). Because of habitat destruction (Grassland) it seems to be in rapid decline here in Victoria.

Despite the lack of correlation with available pics, it fitted descriptions very well in terms of features and habitat. What the books told us was a shot of the outside wing was required for a definitive ID - on the outside it is quite yellow with one white spot right in the middle of the wing (in fact its other common name is the 'Rare White Spot Skipper'!). See this link for a good pic of what we mean:
http://lepidoptera.butterflyhouse.com.au/hesp/lutea.html


So, on Christmas Eve, Russell went back to look for it and to get a pic of the elusive 'rare white spot'! Unfortunately there was no sign of it. However, while looking for it he saw two other butterfly species he'd not seen in Riddells Creek previously. One was a common grassland butterfly called the Grassland Copper (which he'd seen on grasslands before, just not in Riddells Creek) but when he got back he IDed the other as the Amethyst Hairstreak (Jalmenus icilius - pictured right), another rare and FFG-listed species that is rarely seen in Victoria nowadays (again because of habitat destruction). On further exploration it seemed this might be a very significant find as it seems it hasn't been recorded in the Melbourne region since 1900. The butterfly didn't look much except it gave a nice flash of metallic blue when it flapped its wings. The butterflies were flying between and around Blackwoods (Acacia melanoxylon). On one plant he noticed a caterpillar with attendant ants (pictured below left - ants look after the caterpillars of many in this family of butterflies). Blackwood isn't listed as a food plant (which is a significant new finding for this species in itself). What's more, the two-volume reference book "Butterflies of Australia" states that "it is no longer found near Melbourne where it was once collected at Brighton (1893-4), Eltham, Broadmeadows and Gisborne (1900)."


The IDs were confirmed by the Victorian butterfly expert, Ross Field (currently finishing a new book on Victoian Butterflies), who felt it so significant that he visited the site with Russell on Jan 5. Ross has since told us that both species "were

recorded from Mt Piper (Broadford) in the 1990's but there are few extant locations of either species in southern Vic in the past 15 years". He is aware of one population of the Yellow Ochre at Traralgon

and Amethyst Hairstreaks near the Grampians.


The Yellow Ochre butterflies finish flying in mid-December so seeing them on Dec 16 was quite lucky but, curiously, they are likely to reappear in Feb-March. Their food plant here will be Lomandra filiformis or, less likely, Lomandra longifolia.

The Amethyst Hairstreak would be expected (until this find) to be found only on Acacia pycnantha (Golden Wattle) in this area (Acacia mearnsii, Black Wattle, is also listed as a food plant but not in Vic apparently, but worth a look). Our locals are on Acacia melanoxylon (Blackwood). They would be unlikely to be found on planted populations because they stay at their 'birth plant' (probably a factor in their demise) so there aren't many grassland areas left around here that could support them. They are only found on small or young Blackwood plants, not tall or mature plants. They are likely to be seen until mid-late Jan and possibly to March in a good year.

Both are about the size of 20c piece (ie. quite small but twice the size of the very small Grassland Blue butterflies that flit around lawns and in the grasslands, usually close to the ground).
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