ISLAND CONSERVATION-Strange life forms – but not from another planet |14 September 2009

This is not an episode from a science fiction film but a cockroach’s-eye view of an approaching domestic huntsman spider or bibouk. It is not generally known that most spiders have eight eyes, although some species have only two, four or six – and some cave spiders have no eyes at all because they do not need them, since they live in constant darkness. Seen close up, eight eyes glinting at you in the light of a torch can be a little disconcerting, but I don’t suppose most people get that near to a bib or bibouk – the look of which is far worse than its bite, by the way.

Indeed, these house spiders, although not part of the native fauna of the islands, are very useful in that they feed on household cockroaches.

While our spiders are not unique in having so many eyes, we have a cockroach with a very unusual eye arrangement. This is Alluaud’s cockroach, discovered by French entomologist Charles Alluaud on Mahé in 1892 but since then collected on Silhouette as well. You would have to look very hard to find it, because during the day it hides among the dead leaves still hanging from endemic palms.

On returning to France with a male of this species, Alluaud – himself a beetle expert – sent it to the Spanish grasshopper and cockroach specialist Ignacio Bolivar. As he examined it under the microscope, Bolivar was astonished to find that the two compound eyes of the insect are joined to form what you could call an eye-plate right across the forehead. In the female, discovered later, the eyes are very close together but do not quite meet. Alluaud’s cockroach has no known close relative.

Remarkable

Talking about grasshoppers, they hold an anatomical surprise of their own: their ears, necessary to hear the mating songs of their own species, are situated on each side of the front part of the abdomen. Think of your ears lying some way below your armpits! With crickets and bushcrickets, things get even weirder – their ears are situated below the knees of the front legs. But, again, these are general trends in the world of kasbol and grele and so our native species are not in any way exceptional when it comes to where their ears are placed. For a really remarkable anatomical feature we have to turn to a Seychellois member of an obscure group of insects called caddis flies.

“Mostly brownish, moth-like insects” is a typical description that comes up when somebody asks what caddis flies are like. These insects, called trichoptères in French, do not have a Creole name. Their larvae live in water inside little cases made of plant fragments or grains of gravel, while the adults fly around mostly at night. In 1974, the Vienna University Expedition from Austria led by Professor Ferdinand Starmühlner collected four unusual looking caddis larvae from a stream at Casse Dent on Mahé. A much larger number was collected in other streams by the Belgian caddis fly expert Georges Marlier in 1976.

What mystified Marlier was that the larva in question had an amazingly extensible neck, with the front portion capable of being retracted into the rear part, or stretched out so as to double the normal length of the animal! Another peculiarity was the hook-like second pair of legs that vaguely resembled the front ones of a praying mantis. Marlier suspected that the caddis larva, too, was a predator. But this could not be confirmed without observations of living specimens.

Suspense

Sixteen years went by before another Austrian, Dr Hans Malicky, wrote to me, explaining that he wanted to visit Seychelles to study the biology of our strange caddis fly. I helped him to obtain the necessary authorisation and he arrived in December 1992. He promptly caught a few caddis larvae and put them in a bowl of water with various other aquatic creatures, such as other insect larvae and shrimps. The caddis larvae immediately began to investigate their surroundings, but withdrew every time they detected the movement of another animal. The suspense mounted.

Then one of the caddis larvae came upon a dead mayfly nymph. Dr Malicky watched in fascination as the larva gnawed a hole in the body of the nymph, stuck its head right through the opening, and proceeded to devour the mayfly - from inside. The mystery of the telescopic neck was solved: the caddis fly larva feeds in the manner of vultures, which have long featherless necks that enable them to probe inside carrion. The hook-like middle legs of the larva are used to hold on to the edge of the hole while the head and neck are inside.

Marine

The marine life around us abounds with other examples of strange anatomies. Once, as a child, I was holding a sea cucumber off the beach at Anse Royale when it began to expel its intestines. Not a pleasant experience! I learned later  that some sea cucumbers do this when they feel threatened, to distract the attacker and perhaps even provide it with food, allowing the sea cucumber itself to survive and grow a new set of intestines – a case of regeneration, like when lizards grow new tails.

As for the sea spider, not easy to see because of its very effective camouflage, its body is so thin that its alimentary canal and even its sexual organs extend into its legs!

One day “exobiologists” will discover life outside planet Earth. No doubt the living things that have evolved in extraterrestrial conditions will seem very strange to us. But even now, right here in Seychelles, we are surrounded by weird life forms that just don’t follow what we think are the standard rules of anatomy and biology.

by Pat Matyot