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Trilobite Beetles are Happy Being on Land, Alive in the Present Day

The views expressed are those of the author and are not necessarily those of Scientific American.


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trilobite-beetle-ponies

Trilobite beetle Duliticola paradoxa. Credit: Bernard Dupont (flickr.com/photos/berniedup)

I know they look like they belong in the ocean 250 million years ago, but trilobite beetles are actually pretty happy existing in the present day. On land. They hate water, what are you doing? Don’t put them in there. You’ll kill them if you do that. Found in lowland forests across Southeast Asia and India, these peculiar beetles are an enigma wrapped in an armoured shell with the tiniest head and some nice orange highlights.

The trilobite genus Duliticola belongs to the family Lycidae, commonly known as net-winged beetles. This family is a pretty interesting one, because many of its species display huge physical differences between their males and their females. Trilobite beetles are no exception. While the females are easily recognisable – that incredible form is retained from when they were larvae – the males look entirely different. They pretty much just look like plain old beetles, with long, winged bodies and a pair of thick antennae. And all they have to look forward to is growing to 5 mm long. How embarrassing, because the females end up more than ten times larger, growing up to 6 cm long.

Lycidae-beetle

I couldn't find a photo of a male trilobite beetle, but judging from a sketch in a paper mentioned below, they likely look like this beetle, which belongs to the same family, Lycidae. Credit: L. Shyama; Wikimedia

One of the greatest challenges in studying this genus is actually assigning a male and a female to the same species. Other than genetic testing, the only way you can really know for sure that you’ve found a male-female pair is if you happen to catch them ‘doing it’. Either you saw them with their genitals firmly locked together, or you saw nothing. And unfortunately, not many researchers have actually managed to see this process in action. It’s generally accepted that there are lots of species of trilobite beetle in Southeast Asia, but because the males are so nondescript, only a handful have yet been classified.

The only way you’re likely to catch a couple of trilobite beetles mating is if you’re willing to spend a lot of time with them. In 1996, Alvin T. C. Wong from the Department of Zoology at the National University of Singapore followed a number of female Duliticola hoiseni trilobite beetles in the rich, humid forests of Peninsular Malaysia and Singapore, and provided one of the first comprehensive reports of the trilobite beetle lifecycle. According to Wong, they hatch from their eggs in tiny trilobite form and spread out to begin a life lived almost entirely on and around rotting logs and leaf litter. What these beetles actually eat is pretty controversial – some say they’re predators and will eat snails and other insects, while others insist that they’re far more passive, living off fungi, slime mould, or rotting wood juices.

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A female trilobite beetle - Duliticola hoiseni. Credit: A. F. S. L. Lok and H. H. Tan

At around the five-month mark, says Wong, the larval D. hoiseni females will begin to look really bloated and their outer membranes will have stretched to their absolute limit. So they’ll curl up under a piece of wood and remain there, unmoving, for two to three days as they shed their old exoskeleton and develop a new one. After they’ve gone through a series of moults, the females will once again look fat, but this time it’s not their insides outgrowing their outsides – their abdomens will be swollen with a mass of unfertilised eggs.

The newly mature females will then emerge from their shelters and begin a kind of courting display that involves raising their abdomens into the air to expose their gonopores – a genital pore found on the underside of many types of insects. They may or may not excrete some kind of clear liquid at this point too – it’s so far not been confirmed – but if so, this could allow them to disperse pheromones to attract any lurking males. They’ll display like this for four to five days before excreting those unfertilised eggs on the surface of the wood.

As part of his observations, Wong caught a number of females and used them to entice nearby males. One couple eventually found each other and mated, and it was in every way the complete opposite of a beautiful moment. In fact, you could turn it into a pretty convincing Greek tragedy in about fifteen minutes.

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D. paradoxa and her tiny head. Credit: A. F. S. L. Lok

The male had attached himself tightly to the female’s gonopore using his long, curved genitalia, and held onto her like this for about five hours. About three hours after detaching himself, the male dropped dead. The next day, the female laid a sticky mass of around two hundred eggs in a humid patch of leaf litter before dropping dead herself a couple of weeks later. In this particular instance, none of the eggs hatched because they weren’t fertilised properly, and somewhere a host of trilobite beetle angels cried delicate tears of woe into a decorative water fountain made of clouds.

Oh and yes, those tiny head-looking things in the head area of the female trilobite beetles above are actually their heads. Those things are way too small. They’re also retractable, so the females can literally tuck them under their prothorax for protection from predators or an easy getaway from awkward social situtions.

And finally, here’s a trilobite beetle that just happens to be bright purple. There’s not a lot of information on this sighting, but it could be a newly moulted specimen caught in that brief moment between shedding its old exoskeleton and developing its new one, just like these incredible purple centipedes.

Related posts:

Photographer Nicky Bay’s Purple Centipedes and Singapore Blues

Beetle Battles: The Secret World of Leg Wrestling and Abdomen Squeezing

In North American Katydids, Pink is the Dominant Colour

Bec Crew About the Author: Bec Crew is a Sydney-based science writer and award-winning blogger. She is the author of 'Zombie Tits, Astronaut Fish and Other Weird Animals' (NewSouth Press). Follow on Twitter @BecCrew.

The views expressed are those of the author and are not necessarily those of Scientific American.





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