The largest cockroach in the world is the size of your palm

They're huge aren't they?

No one likes cockroaches. They’re associated as disgusting creatures and are often a restaurant’s worst nightmare. There’s just something about them that gives so many of us the ick.

And it doesn’t get any better.

The giant black cockroach (Megaloblatta longipennis) is the world’s largest cockroach. Apparently from having a rather interesting scientific name, they come in at a whopping 9.7cm or 3.8in in length, and 4.5cm or 1.8in in width. They also have a wingspan of 20cm or 8in.

In addition to having a pretty funny scientific name, the giant black cockroach is the largest cockroach in the world. Drawing by Robert Walter Campbell Shelford on Wikimedia Commons

That’s crazy, isn’t it?

But don’t worry—if you don't live in Central America, you’re unlikely to encounter them. The giant black cockroach is found only in Colombia, Peru, and Ecuador.

And if it's any consolation, they probably won't get any bigger.

While a different species but belonging to the same genus, Megaloblatta blaberoides gives a good indication of how big the giant black cockroach is. Photo by Qualiesin on Wikimedia Commons

Insects like the giant black cockroach can't grow beyond a certain size due to several limiting factors.

One theory points to their open circulatory system, where blood flows freely through body cavities rather than being contained within vessels. In larger bodies, it would be harder for the blood to circulate because gravity would pull it down.

Another theory suggests that insects evolved to be smaller to evade predators. Smaller insects are less likely to be detected and eaten.

It’s theorised that insects evolved to be smaller to avoid being eaten by their predator. Photo by Benjamin Balázs on Unsplash

The insect’s exoskeleton is also a factor. While it provides support and protection, as an insect grows larger, its exoskeleton would need to become thicker, eventually becoming too heavy for the insect to carry.

But the most popular theory involves their breathing and oxygen requirements.

Insects breathe through tiny tubes called tracheae that transport oxygen from the air to their body cells. Once insects reach a certain size, they require more oxygen than the tracheae can supply.

This theory is supported by the fact that super-large insects existed around 300 million years ago, with ants the size of hummingbirds and millipedes as long as small crocodiles.

Giant ants the size of hummingbirds used to exist. Photo by Simon Fraser University - Communications & Marketing on Flickr

So, thank goodness insects in this day and age can’t grow any bigger. Because can you imagine a cockroach larger than the giant black cockroach? I’d probably freak out.