Hawai'i Nature Squad
Identifying 'debris' under stream rocks

By the Hawai'i Nature Center

Caddisfly larvae usually make their homes under rocks at the bottom of fast-moving streams. Hawai'i Nature Center

Detectives Nakea and Naniha, two native Hawaiian stream fish, searched the bed of the rushing stream for signs of movement. The Hawai'i Nature Squad, Aquatics Division, had joined the latest investigation. Detectives Penny Pinao and Andy Anole waited anxiously above. The roar of the water was almost deafening.

A sudden splash followed a liquid thud, and Detective Nakea appeared in front of Andy. "We think we've found moving debris under a stream rock," Detective Nakea said loudly.

Andy remembered Jessica King's letter. The third-grader from Holomua Elementary had turned over a stream rock and saw wormy things crawling out from under plant pieces stuck to the rock.

"We're gonna need help turning the rock over," Nakea shouted. Penny zipped over. "We're ready. Just tell us what to do," she yelled.

"Detective Naniha is securing a rope right now. When you see it, grab it and pull," Nakea ordered as he disappeared below the surface and positioned himself behind the bottom of the rock.

Naniha finished securing the rope and let one end float to the surface. The rope danced in the fast-moving water. "There it is!" exclaimed Andy. "Penny! Fly down, and bring it here so I can help."

The dexterous dragonfly plucked the rope from the stream, and soon both detectives were pulling with all their might.

Under the water, the o'opu pair had dug in with their fused pelvic fins, giving the rock a powerful push. It moved slowly at first, then it rolled over.

Andy and Penny shook the droplets off and went over to inspect the underside of the rock.

Detectives Nakea and Naniha swam over. The rock was barely out of the water, exposing three small piles of what seemed like plant parts and pebbles. A tiny head and three pairs of legs emerged from one end of the debris. "Hey! What's the big idea turning over our shelter?" it scolded.

Penny hovered over the rock and flashed her badge. "Sorry about the intrusion. We were trying to solve a nature mystery, and you were it," she declared. "Can you inform us of your purpose?"

"I am a caddisfly larva. My mother went under the water to lay her eggs on a rock. We hatched and now make our homes under rocks in fast-moving water," she explained. "The ends of our abdomen are like hooks so we can hold on to rocks. We use stream debris, like small stones or plant parts to build our cases. We live in them until we pupate."

Another larva revealed itself, grumbling about being hungry, and then the third one emerged munching on some algae.

Naniha sidled up next to Andy and whispered. "If you're done with your interview we should let them go. I heard they get grumpy if they don't eat."

One of the larvae added, "If you want to see what we turn into as adults come back at dusk. Our adults are moth-like and don't live very long. In fact they don't even eat, they just mate, lay eggs, then die."

"Hawai'i Nature Squad" is written by Kim Welch, Kelly Perry and Ati Jeffers-Fabro of the Hawai'i Nature Center.