Tag: nocturnal

Solving the Mystery of the Hidden Callers of the Night

by on Jun.17, 2012, under Fauna, Invertebrates

Text and images by Amy Prendergast

If you are a resident of suburban Perth, Western Australia, I’m sure many of you will hear following sunset a chirping chorus commence, yet are unable to espy the owner of these nighttime vocalizations. On many a night during my twilight dog-walks, I’d been surrounded by the sounds of what appears to be a cross between a cricket chirp and a frog’s croak, yet no matter how hard or long I looked, staring intently at the location where the sounds seemed to be sourced from, I never saw the mysterious creatures responsible for these nighttime noises. Even when I appeared to be directly over the site from which the calls were broadcast, I still could not locate the creature producing these reverberations!

Then, one night not long ago in my very backyard, I heard the memorable sounds start up. Honing in on the spot where they appeared to be coming from, I noticed a slight depression in the sandy soils characterizing Perth. Before the enigmatic creature could cease its song and leave its location undetectable, I plunged my hands into the sand and scooped up a handful. I felt a squirming in my hand – success! Being nighttime, the light was scant so I raced inside and deposited my handful of sand into a glass jar and with anticipation finally laid eyes upon the identity of the creature (insect, amphibian?) that had thus far foiled my attempts to detect it visually. The sight that met my eyes was certainly not anticlimactic! The creature thus unveiled was a large, robust-bodied insect, about the length of my index finger (5cm), glossy brown, with small veined wings extending to the mid-thorax that completely cover the tiny hind-wings, slightly curled, annulated antennae, and a large, heavily sclerotinized shield (protothorax) extending back from the head over the thorax. The most remarkable feature however was the forelimbs: these were disproportionately large, sclerotinized, “clawed” and shovel-like.

 

I then set to the task of taxonomically identifying this specimen and discovered this creature was a mole cricket. Mole crickets are insects closely related to “true” crickets (family Gryllidae); however, mole crickets are recognized as being taxonomically unique and thus are assigned their own distinct family – Gryllotalpidae. Along with “true” crickets, as well as locusts and grasshoppers, mole crickets are classified in the Order Orthoptera. Unlike “true” crickets mole crickets have poor leaping abilities; but what they lack in the jumping arena is made up with regards to their digging abilities. Like true crickets however the males sing to attract mates, producing their sounds by stridulation: rubbing a row of “teeth” on one forewing against a ridge-like vein or scraper on the other forewing. Calls of mole crickets however are much deeper than those of true crickets.

The reason I previously had never spied a mole cricket was the fact that these nocturnal insects are fossorial, subterranean creatures, spending most of their time not far beneath the surface of the soil inhabiting extensive underground tunnel systems that they dig. The morphology of their amazing modified forelimbs I was so impressed with is an adaptation to their burrowing lifestyle, with the powerful robust forelimbs bearing stout spines enabling them to be effective burrowers.

Following nightfall, males commence calling from just below the surface from the entrance of special vertical burrows they construct. The burrow acts as an amplifying, resonating chamber, broadcasting their calls out into the night in the hope of enticing a female. The amplification of the male’s chirping courtship call is due to the structure of these burrows: using their amazing forelimbs, they dexterously sculpt their burrows into a double exponential horn shape, which causes the burrow to act as a megaphone. Males characteristically commence singing at dusk but will cease after a few hours. Once mated, the female lays her fertilized eggs in an underground egg chambers she has dug and will guard her clutch until they hatch.

The mole cricket family has quite an extensive distribution, with various species of the five recognized genera occurring in Asia, Africa, Europe, North and South America, and Australia. All Australian species are placed in the genus Gryllotalpa. This genus, comprising 22 species, is also represented in Africa, Europe and Asia. However, whilst native to eastern Australia, mole crickets are an introduced species to WA. In fact, mole crickets only recently made their way here, as prior to the 1990s records of mole crickets were nonexistent. The species recorded in WA are Gryllotalpa pluvialis and Gryllotalpa species (australis-group). Gryllotalpa pluvialis males produce strident, rapid, chirping songs, contrasting with the slower, quieter trills of the male Gryllotalpa sp. (australis group) mole crickets.

Whilst being remarkable creatures, I don’t advise picking one up: when disturbed or threatened, in defence a mole cricket will discharge a foul-smelling brown liquid from its anal glands (I was fortunate not to receive this nasty surprise when I snared my mole cricket). One of WA’s introduced species, Gryllotalpa pluvialis, also secretes a clear, viscous substance from its rear-end which likely functions in entangling insect or spider predators.

No longer is the identity of the creatures that produce the chirping cricket x frog-like cacophony an enigma. Whilst they still evade my observation during my twilight wanders, I now know the callers are the mysterious mole crickets whose calls fill the air yet whose remarkably modified bodies remain hidden beneath the sandy soil surface.

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Camera for secret wildlife watching

by on Apr.11, 2012, under Fauna, Information, Magazine, Tools and Technology

I came across something the other day called a “trail camera”. Basically it’s a weatherproof stills/video camera with an infra-red sensor that you can leave outside in your yard or anywhere you like. You program it to take either a series of stills or video clips when the sensor is triggered, e.g. if an animal walks in front of it. It can be used for wildlife watching, farm surveillance, security, etc.  One website I saw suggested you could use it to find out what’s been secretly eating your prize veggies at night!

Output photo/video quality is apparently lower than typically found in today’s ‘normal’ digital cameras, but bear in mind that these cameras are capable of taking video in complete darkness without using normal flash lighting (most use a special ‘dark flash’ that doesn’t affect the animals).  They are also weatherproof, so can be used in ways you couldn’t use your normal digicam or mobile phone.  I think it’s the ability to remotely capture nocturnal activity that appeals to me the most.

Prices seem to range from around $200 to $1000.  Images/videos are saved to a standard SD card.  So you set your camera up, leave it to do its thing, then go back later and retrieve the SD card and upload to your computer and see what you captured.  And because it only records when the sensor is triggered, you won’t just have hours of empty footage like a normal video camera.

I found a couple of Aussie websites that are selling them.

http://www.wildguard.com.au/

http://www.wildlifemonitoring.com.au/

Anyone out there using one of these?  Send us your thoughts.  Or lend us one to review!!!

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