Saturday, August 25, 2012

Saturday Hopalong: Leaping from obscurity

In the beginning was soil - 1st stage nymph of grasshopper
Following fast on the first warblers, Autumn's first cold front has brought gloom, chilly winds, and showers to the Home Bug Garden. Bees are huddled on flowers and butterflies nowhere to be seen. Still, if the dimming sun manages to burn its way through the clouds this week, one of our largest insects may make an appearance, at least when startled into  a leap to safety. For the hopper has been around all summer, but rarely noticed.
Crypsis works best when insect and background share a long history
Western North America is famous for its plagues of migratory grasshoppers. Better known as locusts, grasshoppers in the genus Melanoplus ('black + add' or 'blackener', as when the skies are filled with locusts) may alternate between low-level populations of solitary individuals doing little harm and hordes of rampaging beasts. Although the most infamous of these, the Rocky Mountain Locust (Melanoplus spretus Walsh, 1866), is now extinct (as marvellously chronicled in Jeffrey Lockwood's Locust), we have others that breakout of their solitary mode from time to time. The Two-stripped Grasshopper Melanoplus bivittatus (Say, 1825) is one such and a large one at that.
Late stage nymph of Two-striped Grasshopper
Like other grasshoppers, the Two-striped starts its life as an egg in a pod in the soil. When they first hatch in May their colouration helps them to blend into the soil and snow-crushed detritus of last's years vegetation. But as they moult into later stages they green-up into the new foliage. As adults they change again to match the mostly vertical lines of their preferred grassy meadows and fields.
Large size + converging stripes are good field characters
Several dry, hot summers are thought to be needed to induce the migratory outbreak populations. When this grasshopper outbreaks it is a serious pest that will destroy field crops and gardens. But since the last two summers have been wet and often cool, it is reasonable to assume the hoppers natural enemies will hold them in check next year. So, this Fall we can just enjoy them as large, interesting grasshoppers, leaping up from garden and field and maybe munching on as many weeds as crops.
Two-striped embracing an evil weed - Canada Thistle

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