Some bugs are unusually big, others are utterly terrifying ... and some are just downright bizarre. Coming to you from deep in the tropical jungles of Asia, behold the trilobite beetle:

What's not to love about that armour-plated carapace and long, spiky abdomen? 

These strange insects can grow to over six centimetres in length, and they can even retract their tiny heads inside their armour like a tortoise. Whenever a spike-covered animal of surprising size shows up, you can count on someone calling them "prehistoric" – and in fact, these insects are named for a prehistoric creature: the trilobite.

Despite that moniker, the beetles are not close relatives of trilobites, which aren't even insects at all! Famous for their crazy variety of strange armoured forms, trilobites are some of the most ancient complex animals in the fossil record. Evolving around 520 million years ago, they finally went extinct shortly before the first dinosaurs showed up.

The trilobite beetle Platerodrilus paradoxus (top). Image: michel candel, Flickr. A trilobite fossil at the Oxford University Museum of Natural History (bottom). Image: Pippa Sutt, Flickr

Trilobite beetles never saw the Age of Dinosaurs either; they're estimated to have first evolved only 47 million years ago, long after the last of the non-bird dinosaurs died out. They may not be as ancient as T. rex or real trilobites, but they are certainly unusual. For one thing, much like the famous dinosaurs of Jurassic Park, all the prehistoric-looking beetles are female. The males look like unimpressively ordinary netwing beetles, and are typically just a few millimetres long.

The females, on the other hand, exhibit a developmental strategy called "neoteny". While most beetles metamorphose from larval form to adult, lady trilobite beetles never make the change: they just keep getting bigger and bigger, eventually growing sexual organs on their huge grub-like bodies. (Trilobite beetles aren't the only animals that stay young. Many insects have a habit of never developing their adult wings if their environment doesn't call for it. And the famous axolotl salamanders – which are very common pets – never grow out of their gilled aquatic juvenile stage.)

Female and male trilobite beetles are so different that it's nearly impossible to tell which males and females belong to the same species. Without DNA testing, the only other option is to catch them in flagrante, which is rare, but not unheard of – and as you can imagine, a 5mm male trying to mate with a towering female grub-adult can be a bit awkward. In one of the very few reported cases, a researcher named Alvin Wong observed a male firmly attached to his supersized mate ... for five hours. Just a short while after letting go, that tenatious trilobite beetle died.

In short, these insects are truly among nature's weirdest wonders. They even come in different colors!


Top header image: michel candel