Maggie and Bailey Dowling, of Naseby, asks :-
What are the bugs we found in the bottom of Nan and Pops water fountain? They are like a stick, and walk along the bottom of the water.
Gerry Closs, an ecologist at Otago University's Zoology department, responded.
The small insects in the picture are the larvae of case-building caddisflies (known scientifically as Trichoptera), the adults of which are commonly seen flying around bright lights at night, and often confused with moths. Over 240 species of caddisfly live around New Zealand in a wide variety of freshwater environments, including water fountains in Naseby!
The case-building caddisflies (the ones in the picture are most likely Triplectides obseletus), mostly consume algae and decaying plant material. Their case is made of silk, to which they attach small pieces of wood, leaves and sand. The case provides protection from predators, including fish and dragonfly larvae, both of which eat caddisflies. The attached leaves and sticks are no doubt a very effective camouflage, and as long as the caddisfly remains tucked inside their case, they can remain well hidden. The tubular case may also assist with breathing. As the larvae undulate their abdomens inside the case, water is sucked in at the front end, drifts over and oxygenates their gills, and then out at the rear end.
Case-building caddisflies larvae live for up to a year or more. Eventually, they retreat into their case, close it up with silk and pupate, just like a butterfly or moth to which they are closely related. When they hatch from their pupae, they swim to the surface and fly away. They look like small moths, although their long filamentous antennae give them away as caddisflies. When ready to lay their eggs, they return to a lake or stream and fly around just above the water, usually in the evening. At this time, they are vulnerable to surface feeding trout which splash and jump in an effort to catch them. You can watch feeding trout and caddisflies on still evenings in Coalpit Dam close by to Naseby.