Aquatic Insects On The Move

The recent spate of dry weather is reducing the marshy hinterlands to the usual dry grasslands. As a result aquatic insects whose numbers have grown considerably over the recent wet season, are taking to flight, probably to find more suitable habitats.

Most of the flights take place at night. Many of these nocturnal wanderers are deflected from their flights by electric lights. This has resulted in some unusual visitors.

Recently Pygmy Grasshoppers have descended on the region in their millions. They frequented the lights around service stations in the Cairns district as well as along the storefronts on the main street of Atherton. All of the specimens I found were of the widespread Australian species Paratettix nigrescens Sjostedt.

The Pygmy Grasshopper, Paratettix nigrescens Sjostedt; family Tetrigidae.

Pygmy Grasshoppers are, as you would guess, small. This fellow measures about 8 mm in length. These insects feed on algae and diatoms along the margins of streams and lakes. They also invade on marshy ground-so long as it stays marshy where their numbers can swell. In Australia, they can often be found on perennially wet lawns. [Note the pad-like forewing called the tegmen.]
Most pygmy grasshoppers occur in a number of colour morphs. This affords camouflage on gravelly substrates where they are virtually invisible until they fly.

Along with the grasshoppers there has been an unusually large number of water beetles showing up at the lights.

Gyrinid beetles rarely appear at my lights even though a stream is only about 20m distant. But around 10 May many could be seen. These are the beetles you see on the surface of lakes or in quiet areas of streams where they feed on particulate matter that drops onto the water. They, in effect, have four eyes. Each eye is horizontally divided into two. Half is above water, the other half below. So the beetle can scan both worlds. When threatened, the beetles dive underwater and hang onto a branch or rock until the danger passes, then they release and float to the surface.
Many other water beetles, primarily in the families Hydrophilidae and Dytiscidae, fly at night.
This is the colourful dytiscid water beetle, Hydaticus vittatus, a common water beetle over much of eastern Australia.
This is a Pygmy or Dwarf Cricket, Pteronemobius regulus (Saussure). This genus is cosmopolitan with species occurring around aquatic habitats throughout the world. They don't often enter the water but live on mucky ground around the margins of streams and marshes. Several species often live sympatrically at a given locality. Males sing with distinctive soft continuous or pulsating calls, heard mostly at night.