16 February 2010

Yellow-winged Locust - Gastrimargus musicus

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Yellow-winged Locust - Gastrimargus musicus

A common widespread locust found in all mainland Australian States. There are two distinct forms, one being the solitary ‘non-swarming’ variety and the other the ‘swarming’ plague agricultural pest. The latter tends to occur in the more northern latitudes where there is heat and summer rainfall; both needed for breeding purposes. Further south where rainfall is winter dominant, it is usually too dry for a successful mass egg-laying during summer and too cold during winter. But the solitary locust can be common in southern areas, even to become local pests, but they are far from being in plague proportions (more than 50 individuals per square metre/yard), when they can really do some damage.

The Yellow-winged Locust is easily recognised by their bright yellow wings and black border, which are clearly shown as they take off a metre or two in front of you, when walking along sedge or grass covered tracks. They flutter several metres/yards before dropping to the ground, only to rise again and repeat the process when you approach. This flight habit makes them very difficult to photograph in their natural surroundings, or to catch by hand without dramatic dives to the ground. Even if you do manage to grab one, it is usually more luck than good judgement.

At rest, the Yellow-winged Locust is similar in appearance to Locusta migratoria the Migratory Locust, although a little smaller, the latter mostly over 5 cm (2”), whilst the former usually around 4 cm (13/4”). There are several other noticeable differences, but these can be highly variable, therefore several features need to be considered together. Besides distinctively coloured wings (Migratory Locusts have a clear or pale yellow wing, without a border), the markings on the face, wings and rear legs usually differ, as do the shanks or tibia that are bright red/purple on the Yellow-winged, and pale pink or yellow/brown on the Migratory. From local Esperance observations where both species occur, only the Migratory Locust are attracted to house lights, as I have never encountered the other despite it being more common.

Beside behavioural differences between ‘swarming’ and ‘non-swarming’ yellow-winged locusts, there are physical differences too, the most obvious being the ridge (pronotum) behind the head on the thorax, which is not there (the area flattened) when swarming. When conditions are right, plague proportions can develop remarkably quickly, with only 11 days from the laying of eggs to the emergence of the hoppers, and another 40 days before those hoppers turn into adults, with only another 12 before these adults begin laying eggs of their own.