Australia’s vibrant and cute spider-form of sexy male peacocks
By Amy Prendergast
The male peacock is the classic example of how under sexual selection males have evolved spectacular gaudy adornments to impress choosy females.
Evolution of extravagant courtship displays and coloration signalling a male’s sexiness to seduce females is ubiquitous throughout the animal kingdom and is by no means restricted to birds. An epitome of sexual selection in favouring astounding male courtship displays and appearance occurs in peacock spiders. Whilst measuring a mere 5mm, like their namesakes, male peacock spiders are arguably even more outrageous when it comes to bright appearances and behaviours to entice the comparatively drab brown (yet well camouflaged) female peacock spiders to mate with them.
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.
The Many-legged Myriapods
Whilst centipedes and millipedes have jaw-like mandibles on their heads for feeding like insects and crustaceans, they are classified in their own Arthropod subphylum: the Myriapoda. In additional to centipedes (Class Chilopoda) and millipedes (Class Diplopoda), the Myriapoda also includes two other little- known microscopic classes: symphalans (Class Symphyla) and pauropodans (Class Pauropoda).
Myriapods are immediately recognizable by their long, segmented bodies, with each segment possessing one or two pairs of jointed legs. The name Myriapoda is derived from Greek murias meaning ten thousand, + Latin pod meaning foot. As the name of this group suggests, these animals have a myriad of legs but whilst nowadays a ‘myriad’ denotes something countless or extremely great in number, a myriad classically referred to a unit of ten thousand – and no myriapod even comes close to possessing this many legs. Actually, some myriapod species have as few as 10 legs in total. The record for the greatest number of legs is held by a species of millipede: Illacme plenipes, which has 750 legs. This extremely rare, species of millipede is restricted to a tiny area in California. Illacme plenipes was thought to be extinct as it had not been seen for over 80 years since its initial discovery, and was only rediscovered in 2008. Illacme plenipes not only has the greatest number of legs of all myriapods, but also in fact holds the world record for the greatest number of legs of any animal! During locomotion, the legs move in waves that travel down the length of the body. It’s amazing that they can travel, often considerably rapidly, without getting all those legs tangled up! Their coordination is quite remarkable.