“When, by a singular turn of Fortune’s wheel, I landed on the shores of Borneo, I swore a solemn oath to the gods of entomology to unveil the mystery of the ‘trilobite larvae’ and disclose their identity.”

THESE WERE THE words of Dr Eric Mjöberg, the Swedish explorer and naturalist who succeeded in solving one of nature’s great mysteries. The trilobite larvae had kept the world of science puzzled for nearly a hundred years until Mjöberg unveiled the mystery in 1924, in the rainforests of Sarawak.

With this breakthrough, the world learned that trilobite larvae were female insects that had grown to maturity while retaining their juvenile or larval form, a phenomenon known as neoteny. Before that, entomologists had postulated that they “plainly represented the larva-form of some unknown insect”.

These exotic creatures taken from the Far East were displayed at scientific meetings in England in the 1800s. And scientists kept living specimens under constant care and observation in the hope of seeing them change into adult insects. Some of them survived for as long as two years but they all eventually died, taking the secret of their real identity with them.

They were initially nicknamed “Perty’s larvae” after the English entomologist who described one of the first specimens in 1831 as larva singularis, or “the remarkable larva”. Later they were called “trilobite larvae” because of their resemblance to the long-extinct, fossilised sea creatures of the Cambrian Period.

MJÖBERG EXPLORED the Malay Archipelago for eight years. His book, I Tropikernas Villande Urskogar, was published in Stockholm in 1928. The excerpts used here are taken from the English version, Forest Life and Adventures in the Malay Archipelago, published two years later. They reflect the resolve and “stubborn persistency” with which he pursued his objective.

In a chapter devoted to the trilobite larvae, he described how he trekked through the jungles of Sarawak in rain and shine, climbed mountains and camped out in the rainforests with his porters and his specimens of trilobite larva.

In October 1922, he was travelling with 70 porters towards Gunung (Mount) Murud when “Heaven’s gates were opened and masses of water were literally crashing down”.

“A giant tree, that had fallen, barred my way, and I stopped, as at the same time I had discovered a ‘trilobite larva’. It was one of the prettiest sights I had ever seen. Its little head, which it could draw in or push out at will, was extended, and it was feeling about with its front legs, as if to see how the land lay. Its body was a glossy black, as though it were varnished, and crossed by bright crimson spots. My bearers stood in open-mouthed amazement, and could only exclaimed, ‘olar, toewan’ (‘a snake, sir’).

“I took the little beast with me and marched on,” he wrote.

Several days later on Mt Murud, he promised his porters one penny for each specimen they could bring to him. This was 1922 and one penny was hardly a sum to be sniffed at. In fact, his reward offer “aroused such a frenzy of zeal, that within a week I had several hundred larvae shut up in a cage”.

All these specimens died, but this led to an important preliminary discovery – they were all mature females as their ovaries were full of eggs that had remained unfertilised.

Mjöberg wrote: “The result of the trouble with several hundred larvae had, however, been all to the good. For it had shown me clearly that these curious ‘trilobite larvae’ never developed into pupae and fully developed insects, but were propagated in neoteinic forms – that is, as larva-like creatures.”

SEVERAL MONTHS later, he had another batch of trilobite larvae which had grown to maturity. “It was not long before they began to lay great quantities of eggs about as large as sago grains, and thus gave definite proof that they were fully developed insects. Every female laid as many as four hundred eggs.”

All these eggs did not hatch as they had not been fertilised, and this ruled out parthenogeny (virgin birth) as the reproduction process of these enigmatic creatures.

So what Mj’berg had to do now was to find the male insect and the mystery would be solved. But that was easier said than done. He had to find more specimens, trek to localities where he believed he could find the males, and make cages of “large-holed, perforated metal to allow free entrance to possible males if there were any in the neighbourhood”.

In mid-1924 (probably June) on Mount Poi in Sarawak, Mjöberg had about 20 trilobite larvae placed “on view” to attract the males. Arriving at the site he “made a few improvements with respect to technical details”. This attention to detail paid off the following day, ending Mjöberg’s quest for the male and the answer to a nearly-century-old riddle. And the moment of truth as Mjöberg described it:

“Imagine, then, my delight and surprise, when next morning I saw a pitiable little, blue-black creature sitting firmly on the pointed posterior of the female. Thus, after nearly two years’ work, I had at last succeeded in surprising the rare male in flagranti. There could be no doubt of their mutual connection, but what an unheard-of contrast: a whitish-yellow, clumsy, unwieldy female full 2½ inches long, and an elegant steel-blue male no more than 1/5 inch in length, with gigantic eyes and distinctive antennae, a well-made beetle in every way.

“Nature sometimes follows strange paths to reach her goal.”

Duliticola paradoxa is the name he gave to this species of trilobite larva that finally yielded the answer he sought. Mjöberg had wanted to continue his research but could not do so as he had to return home to Sweden. Today, three-quarters of a century after Mjöberg’s discovery, there are still some unanswered questions about the trilobite larva.

They were initially believed to feed on the rotting, crumbling wood in which they are often found. Later it was believed that they feed on small animals and fungi that flourish in rotting wood. More recently, one scientist said that these creatures, with mouth-parts adapted only for sucking, actually feed on the rich micro-fauna of copepods, rotifers and protozoans present in the juices of rotting wood.

Southeast Asia is the centre of diversity of these peculiar creatures which belong to the family Lycidae (net-winged beetles of the Order Coleoptera). No one can say for sure how many species there are. The males are rarely seen because they are quite secretive and nocturnal in habit.

The remarkable trilobite larva is very much an entomological enigma to this day.

So what does the male “trilobite larva” look like? Click here to find out.