Dear David,
I like big bugs. I cannot lie.
But which insect is the biggest? I asked my friend Rich Zack. He’s an insect scientist at Washington State University.
He told me the answer depends on how you define big.
One way is how much matter makes up an insect’s body. The insects with the most body mass are giant beetles. These include titan beetles, Goliath beetles, rhinoceros beetles and elephant beetles. They can be the size of a mouse.
“Some of these beetles are so big and strong that you try to hold that thing in your hand, and it can use its legs to push your hand open,” Zack said.
Another way to define big is weight. The heaviest insect ever recorded is a cricket-like insect called a giant wētā. The biggest one weighed about 2.5 ounces—about the same weight as five empty soda cans.
If you measure an insect from the tip of one wing to the tip of the other wing, the biggest is the white witch moth. It can grow to 12 inches across—about the same as the height of one two-liter soda bottle.
The longest insects are stick insects. The longest insect ever recorded measured more than 25 inches long. That’s about as a long as two two-liter soda bottles.
The biggest insects tend to live in tropical places. Without freezing winters to worry about, they have time to grow bigger and bigger.
But there’s a limit to how big they can get.
“Right now, the more common theory is that insects are limited in size by their ability to get oxygen into their bodies,” Zack said.
Mammals like us use our lungs to take in oxygen. Then we use our blood to move the oxygen around to all our cells.
Insects don’t have lungs. Their blood-like hemolymph doesn’t carry oxygen. Instead, they take in oxygen through a row of holes that sit along their sides—called spiracles. The spiracles connect to a series of tubes that get smaller and smaller. They pipe oxygen to every cell in an insect’s body.
The larger an insect gets, the more tubes it needs. Those tubes must fit inside the insect along with all its other internal bits. It’s an especially tight fit at the super narrow spots on an insect’s body, like where its legs and wings attach.
One thing we all use oxygen for is to make energy from the food we eat. Zack told me that really big insects struggle with energy and getting around. They tend to be slow-moving and even clumsy.
About 285 million years ago, dragonfly-like griffinflies were probably about the size of today’s falcons. Back then, there was more oxygen in the air than we have now, so it was easier to get bigger.
Which is ok because I like little bugs, too.
Sincerely,
Dr. Universe