Tuesday, December 7, 2010

The Longest Insect in the World?

On a cold morning in June 2010, sitting in the back of an open vehicle in Tarangire National Park, the guide trainee who was attempting to impress us with his guiding skills stumbled upon this magnificent creature. I had never seen a stick insect so long and my first thought was that it could be a new species.

After taking photos with my hand in the picture for size comparison (and we didn’t play any visual tricks), I decided to try to hold it. Carefully reaching in, I put my fingers on either sides of its thorax to pick it up. This way, I thought I would be able to hold it without hurting the insect. In a rapid movement it lifted the two scales that look like thorns and spread its wings, which startled me, so I quickly pulled my hand away.

Stick insects belong to an order called Phasmatodae. They are vegetarians and are most active at night- when it’s even harder to see them. This particular individual comes from a genus called Bactrododema or Palophus.

Check out the "thorns" just like on a Wait-abit-Acacia (Acacia mellifera). If you look carefully at the "thorn" above the finger after the joint you can see the insects eye. 

My hand is about 8 inches long- that means the stick insect is at least 16 inches long.

Without knowing anything about the specific insect, I was excited to be able to describe two defense strategies that this insect uses. Stick insects are actually one of the most vulnerable insects. They can’t jump, they can’t fly, they don’t bite, and they don’t sting so they have to rely on a different method to hide from their predators- mainly insect eating birds. The strategy that most use is merely camouflage or cryptic coloration. They blend into the environment and mimic either grass or twigs and as a result we hardly ever even notice them.

When we found this giant stick insect, it was doing what stick insects do and blending. It had its front legs and antenna stretched out in front of it, and was holding its body rigid, just like a stick. Even when we touched the growths on its body that looked like thorns it remained completely still, until I tried to pick it up. If pretending it was a stick wasn’t going to work, it was going to have to do everything it could to scare me. Spreading its wings quickly, accompanied by a sound as though someone was crumpling some newspaper, was enough to make me quickly move my hand away from the insect. Looking carefully at its wings you can see that they are torn and it’s obvious that this insect doesn’t use its wings to fly. I expect the flash of color also serves to visually startle its predators.

Bactrododema sp. aka African pretender.