27 June 2009

Migratory Locust - Locusta migratoria

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Migratory Locust - Locusta migratoria

The Migratory Locust occurs in the warmer, somewhat arid regions of the world and often in plague proportions. It has two phases with the plague one called the Gregarious Phase and in Australia this is restricted to the western outback area of Queensland. The other, the Solitary Phase or non-swarming phase, is more widespread and has even been recorded south of Perth, but according to Dr David Rentz (who kindly identified my photographs) they are not recorded for the Esperance region, however they are not uncommon here, plus I have records of them going back several years. Perhaps they have been misidentified as the Yellow-winged Locust - Gastrimargus musicus, which although smaller, are when at rest, very similar to the adult Solitary phase of the Migratory Locust, but when in flight their yellow wings are quite distinctive and so they are easily separated.

Locally Migratory Locusts can be found in numbers during the warmer months from January to April and although they can still be encountered during May, they have become very slow and are fast losing muscle control, making them easy prey for predators like Magpies. They can grow to over 7 cm (3") in head/body length, so are a good meal for many a predator and no doubt would help greatly in building fat reserves to carry them over the scarce insect winter months.

Color variation is a feature of all locusts and is largely dependant on their phase, temperature and nutrition. In their plague Gregarious Phase they are yellow to orange in coloration but are not found locally. The Solitary Phase adults come in various morphs from brown, to grey, to green, with the green morph probably having had greater access to higher nutrition levels in the nymphal stage and likely represents a higher coastal rainfall background.

Male and female locust are easily distinguished as the females have a couple of small projections at the end of their abdomen (much like male crickets), whereas the male locust has a smooth and rounded rear, due to a protective plate that conceals the reproductive organs. A male and female example has been notated above.