ISLAND CONSERVATION-The praying predator – a new arrival raises questions |28 December 2009
It was at least seven centimetres long, bright green in colour, with a noticeably swollen abdomen – a well-fed female, no doubt, and much bigger than our native praying mantis! I almost shouted out to the SBC driver to stop, so that I could get out to take a closer look. But I quickly stifled my emotion, even as the car drove on, past the Trwa Zwazo Bicentennial Monument. What would my SBC colleagues think? And could I just be imagining things, or exaggerating the size of the mantis to myself somehow, because I had been spending days on end studying mantids on Cosmoledo, Aldabra and Assomption?
Months went by. I often thought about what I had seen, or thought I had seen, on that flamboyant tree – but nothing came up to shed any light on the matter. Then, on September 7, 2004, Ronley Fanchette and Perley Constance from the Ministry of Environment dropped by to see me at the SBC station at Hermitage. Ms Marie-Yvonne Fréminot at M & N Tailoring behind Habib Bank in town had called to report finding a strange insect on the door of her workshop. They had gone there and collected it.
I peered inside the jar they handed me. It was a case of instant recognition – almost the same size, the same green, just as plump, this was the same kind of mantis as the one I had seen nearly two years before!
Not native
All sorts of questions came to mind. What species of mantis was it? And was it another invasive alien? I suggested we take a closer look at the specimen. The front legs often have features that are useful for identifying mantids, I told them. With Ronley’s nimble fingers wrapped around the creature’s abdomen, we gently parted the front legs that were folded and held close together in typical “praying” mode. Amid the formidable-looking spines we found a useful identification feature all right: two absolutely white rounded patches on the inner side of the left leg, and three similar ones on the right. This, together with the shape of the thorax as well as the size of the insect, was proof that the mantis was not the native one we were familiar with.
There were not going to be any more two-year gaps in my observations. Just three days later, on September 10, 2004, as I was leaving SBC Radio at Union Vale just after 9 p.m., I found another specimen of the new mantis on a wall just under a light.
This one was brown, and it was a male. The very next day I discovered a mantis egg-case on one of the twigs of a kalisdipap tree between the Pirates’ Arms and the Supreme Court: it was smooth and dark brown and had a varnished sheen, quite different from the egg-case of our native mantis. And the next morning, I saw that the female that Ronley and Perley had left in my care had deposited an egg-case of its own inside the vivarium in which I had placed it: it was similar to the one I had found near the Pirates’ Arms! Clearly, both sexes were present on Mahé, and the species was reproducing. I soon realized how prolific it could be.
My captive female fed eagerly on not only houseflies but also bush crickets, longhorn beetles and cockroaches, including the large American and Australian cockroaches that are household pests. It laid four more times, mostly at intervals of less than two weeks. When the first egg-case hatched on October 10 , about a month after it was laid, I counted at least fifty baby mantids milling around all over the inside of the vivarium, for all the world like a swarm of yellow crazy ants or fourmi Maldiv.
On November 11 Ronley Fanchette from the Ministry of Environment showed me another female mantis. This one had been found by Christelle Rose at the Import Section of the SMB. Whether we were dealing with an invader or a new species that had arrived in Seychelles naturally, Victoria and its environs seemed to be a focal point of its distribution. Ronley and I wondered what could be the long-term impact of the new species on the smaller native mantis and other insects. A praying mantis is actually a preying mantis…
Biology
Observing my captive specimens, I noticed that at night the females hanged upside down from the branches I had placed inside their cages and curled their abdomen away from their wings. In the light of my torch I could see slight pulsing or pumping movements. I knew that many female insects twitch their abdomen in this manner as they release pheromones – chemicals that excite and attract males of the same species. Sure enough, on November 22 at 8 a.m. I found a green male near one of the cages containing a female at my parents’ home at La Rosière – it had presumably come in through an open window during the night.
Other interesting observations followed, enabling us to piece together the jigsaw of the biology of the new mantis. From the first batch of baby mantids one reached adulthood just under three months later. When I put a male and a female together in the same cage I discovered that, with this species, too, the female starts eating her partner head-first in the middle of the sex act – an aspect of mantid behaviour that has fascinated people for centuries. But for me the most interesting observation of all was on November 20, 2005 at La Rosière.
A bulbul or merl seemed to be poking its beak at something among the flowers and leaves at the end of a branch of a mango tree. It fluttered from one position to another, seeming to peer among the leaves from time to time. Then something green, apparently an insect, hopped onto the upper surface of a leaf. Even as I was wondering if it was a leaf insect, a bush cricket or a mantis, the bulbul darted at it, then immediately recoiled. The green insect was a mantis and it had struck out at the bird with its front legs! Even as I realised this, it let go of the leaf and drifted to the ground. The bulbul followed and fluttered above where it had landed. I ran over and got there first. It was a large female specimen of the new mantis.
Spread
By then, Dr Alfred Kaltenbach of the Naturhistorisches Museum in Vienna had confirmed the identity of the species – it goes by the longish scientific name of Hierodula patellifera, and is found all over Asia, from India to Japan and the Philippines, as well as on Christmas Island (part of Australia) at the eastern end of the Indian Ocean. Once I knew its identity I could look up what has been published about it in the scientific literature. To my consternation I found an old account that one attacked and killed a sunbird (related to our kolibri) in India. The bird was not eaten, however, unlike a “crying tree-frog” (similar to our krapo) that, according to another report, was “attacked and devoured” in southern China.
One of the questions repeatedly asked about these new species not recorded from our islands before is: how did it get here? Discussing the presence of exotic mantids in the United States, Lawrence E. Hurd, professor of biology at Washington and Lee University, has drawn attention to “the inadvertent distribution of eggs on transplanted nursery stock… and on various modes of human transportation” – in other words, mantids can spread because the females often stick their egg-cases onto plants, vehicles and even cargo that people take from one part of the world to another.
A year ago, Perrin Dingwall found a specimen of the new mantis in his living room at Au Cap. Last week conservationist Victorin Laboudallon was given a male that had been found at Anse Volbert on Praslin. The species has moved beyond Victoria and is now colonising more islands – a reminder that we must never drop our guard against potential invaders.
by Pat Matyot