Summer Visitors

Forest and Bird, Issue 299, 1 February 2001, Page 38

Summer Visitors

By

ANN GRAEME

ANS we t's sumOh Y / ws mer. The xy doors and windows stand wide open. The scent of warm earth and mown grass drifts indoors — and so do the blowflies and other insect visitors. I am looking at the praying mantis sit- — ting on the window sill. The mantis turns her head and looks at me. With her distended abdomen, she is clearly pregnant, and she holds a struggling blowfly in her spiky front legs. Having decided I am neither a threat nor a potential meal, she lowers her head and begins munching the blowfly. I am repelled — and fascinated. ‘This is an insect having dinner, I remind myself. ‘She is not a miniature human sadist.’ For the mantis has such a human-like construction it is hard to remember she is driven by instinct, not reason. The way she swivels her triangular head on a mobile neck is a thing few insects can do, encased as they are in a rigid exoskeleton. Her face, with its large eyes, seems so intelligent because the eyes face forward, like ours do. Most animals have their eyes set on the sides of the head, to provide the all-round field of view which is essential if a predator may be creeping up. But eyes facing forward can focus together, giving a more limited but three-dimensional picture. This ability to judge distance is very useful for climbing animals like monkeys, or

hunting animals like owls and humans and mantises. My mantis is a formidable hunter. Although the window sill lacks the camouflage of a leafy branch, she stalked the blowfly ... slowly ... slowly — then stood quite still. Insects perceive movement more readily than form, and the blowfly, unaware of danger, blundered closer. The mantis’s spiked front limbs, folded so demurely above her tiny waist, shot out in a lightning lunge, and it was curtains for the blowfly! The mantis’s appetite is insatiable. She will catch again and again, carelessly dropping half-eaten flies. And that’s not the worst of it. The nineteenth-century French naturalist, Jean Henri Fabré, wrote: ‘I once surprised a male, apparently in the performance of its vital functions, holding the female tightly embraced — but he had no head, no neck, scarcely any thorax! The female, her head turned over her shoulder, was peacefully browsing on the remains of her lover! And the masculine remnant, firmly anchored, continued its duty. The mating mantises I have seen have never behaved in such a grisly way, though I have seen a female chewing on a fly during the mating act. A New Zealand entomologist, Richard Sharell, recorded finding the males of our green mantis Orthdera novaezealandiae dead on the ground, spent and exhausted after mating. Perhaps, in the ruthless economy of the natural world,

eating one’s spouse usefully pre-empts their approaching demise. The brown mantis Miomantis caffra that I was watching is a species recently arrived as a stowaway from South Africa. Over the past decade this slender, feisty mantis has become increasingly numerous in northern parts of the country and it often comes into the house, where it inconsiderately lays its eggs on the curtains. Outside, dozens of its egg cases are cemented in the corners of the brickwork and under the roof overhang. The more sturdy native green mantis was never so numerous, and now seems even less common. Mantises make the most elegant egg cases. From her grotesquely swollen abdomen, as if from a kitchen whiz, the female produces a foamy mass. Her feeler-like cerci at the tip of the abdomen stir and mould the foam and gradually an oval box emerges consisting of two rows of egg cells, each neatly capped. The foam hardens and the egg cells become clearly visible in the egg-case of the green mantis, The egg-case of the brown mantis remains shrouded in soft foam, however, looking like a blob of whipped cream. It seems the mantises invented foam packaging some millions of years before New Zealand Post. Their foam construction not only insulates the eggs from the cold and heat, and protects the eggs from the winter rain, but also lets in air for the developing larvae which emerge in early summer.

y favourite summer visitors, however, are VI the stick insects. New Zealand has 21 species of stick insect which browse on a variety of native plants, favouring manuka and kanuka as well as introduced plants like willow and roses. In his book, The Stick Insects of New Zealand, Professor John Salmon tells us that stick insects were common throughout New Zealand before the 1950s. Then, when farmers began using DDT to kill grass grubs, they almost disappeared. Although DDT was banned in the mid-1960s, the professor reckoned it was twenty years before stick insect numbers seemed to be recovering and in 1991 he wrote, ‘they are still relatively scarce and hard to come by in many parts of the country. This is a sobering story and I am glad stick insects seem now to be thriving, at least in my garden. Stick insect are masters of disguise. Not only do they arrange their thin, often knobbly bodies to match the twigs and branches, but they act like twigs. A frightened stick insect will stand perfectly still with its forelegs stretched out over its head. Then it may sway gently from side to side creating a very fair resemblance to a twig swaying in the breeze. If this act doesn’t work, (as it doesn’t on the sitting-room wall), the stick insect will ‘play dead’ falling to the ground or the carpet, its legs held out stiffly as if in rigor mortis. I wait ... and wait ... and wait, but the stick insect can stay motionless for an hour or more. So I pick it up, all stiff, lay it on a branch of kanuka, and in no time it scrambles away. Stick insect eggs look like little droppings, and are well disguised on the ground where, without ceremony, the female drops them. To watch a stick insect hatch is to witness a tiny miracle.

When the little creature has struggled free of the egg case, it seems impossible that all those frail and tangled legs could ever have been fitted into such a tiny box! Then it must moult at least four times as it grows to maturity. Extracting those long legs from

the old skin is a very tricky business, and many a stick insect dies, caught in its own skeleton. The female lays a lot of eggs over the summer, many of which are unfertilised and from which only females will emerge. So it follows that the female stick insect is far bigger and stouter than the male, and the matchstick males seem far less numerous, such is the economy of natural selection. Indeed, in some kinds, males have never been found and are thought not to exist, the species apparently breeding continuously by parthenogenesis (laying fertile eggs without mating). Unlike the many winged stick insects of the tropics, all our many stick insects are flightless. Insects like weta have given away flight in favour of increased body size but, by world standards, our stick insects are not that big at all. Perhaps the perils of being blown away on our windy chain of islands have outweighed the advantages that wings bestow. On the Chatham islands, only 20 percent of insects have wings, which shows the evolutionary cost of careless flight on a windswept island! There will be many more of these summer visitors; spiders that fall into the bath, grasshoppers that goggle on top of the TV, even skinks that wriggle over the lino. Throw a tea towel over your frightened visitors, pick them up gently and take them back outside.

ith its air of piety and wisdom, the praying mantis has long been celebrated in folk lore and medicine. Even early naturalists suspended their scientific judgement in its quaint face. The six-teenth-century naturalist Thomas Moffat tells us that children lost in the fields would enquire their way of the mantis. The insect would extend a limb indicating the direction to follow and, says Moffat, ‘scarcely ever was the insect mistaken’.