Tuesday, 17 May 2011

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.

4 comments:

Denis Wilson said...

Hi Dave
I love that you get Water Beetles flying past your place at night.
Seems quite improbable to me. But I do not doubt you for a moment - just expressing surprise at the different mountain environments we inhabit.
Cheers
Denis

Mr. Smiley said...

Thanks Denis. I'm always impressed at what must be going on overhead. I get a couple of locust species and several katydids that don't live in the rainforest. They must just be passing in the night sky and drop in.

What a world we live in.

Camera Trap Codger said...

I've encountered our giant water beetles at the Costco Parking lot at this time of year, Normally I pull them out of the pool filter. Have also had backswimmers crash land on my windshield several times, too. I'll not forget John Polhemus's description of the flying water bugs -- remember that trip?

Mr. Smiley said...

I remember the trip but not the comment. I should remember it as it more than ten years ago. Now what was I doing yesterday......