Trilobite Beetle

No, not at all. Trilobites were marine arthropods that flourished for nearly 300 million years and went extinct at the end of the Permian, around 250 million years ago, long before beetles existed. The trilobite beetle is a modern insect, a member of the net-winged beetle family (Lycidae), and its resemblance to a trilobite is a coincidence of body shape — the female's flattened, oval outline, her overlapping shield-like back plates, and the row of spiny lobes along each side happen to echo the segmented, armoured look of a trilobite. The name is descriptive, chosen because early collectors thought the females looked like little living trilobites.

The female trilobite beetle shows one of the most extreme cases of neoteny (also called paedomorphosis) among insects — she reaches sexual maturity and reproduces while retaining a larval body. She never undergoes the transformation into a compact, hard-shelled, winged adult; instead she just keeps growing larger in her flattened, plated, grub-like form, sometimes for years. The male develops normally through pupation into a small, soft, winged beetle only about a centimetre long, which flies in search of the large, flightless females on the forest floor. Because the two sexes look like completely different animals — and because males are rarely seen — entomologists spent over a hundred years describing them separately before mating pairs and genetics linked them.

The larvae and the larviform females are predators and fungivores. They live in and on rotting logs and damp leaf litter and feed largely by external digestion — flooding a snail, slug, or patch of fungal and microbial growth with enzymes and then sucking up the liquefied result. The females' hard, spiny, flattened armour makes them difficult for many predators, such as birds and small mammals, to handle or swallow, and net-winged beetles as a group contain bitter defensive chemicals and are often brightly warning-coloured, so the trilobite beetle is probably distasteful as well as physically protected. Adult males, being soft and short-lived, are more vulnerable but present only briefly.

They are creatures of intact, humid tropical rainforest, and the great majority of species and records come from Southeast Asia — peninsular Malaysia and Borneo especially, plus Thailand, Sumatra, Java, the Philippines, and parts of India. Within that range the flattened females are found on and under rotting logs, on tree trunks, and among moist leaf litter on the forest floor, usually in primary forest or older, undisturbed secondary forest with abundant deadwood. They are not common even where they occur, they do not come to lights (only the flying males might), and finding one is a notable event for naturalists and photographers. Because they depend on old, damp, deadwood-rich forest, they are among the invertebrates most affected by logging and forest clearance.