Caddisfly turned Cannibal: How climate change could affect animal behavior

Caddisflies are most abundant near well-aerated streams and fast-flowing water, but also frequent lakes, ponds and marshes. When space and resources get tight the insects become cannibals. (Bruce Marlin/Wikimedia, Creative Commons)

Imagine the semester has just begun and you’re out in the forest walking in a freshwater stream and you decide to turn over a few rocks. You’d start to find tiny cylindrical bundles of pretty minerals and you’d wonder whether this was a geological miracle or the workings of some sort of aquatic creature. You’d be right to think the latter. The bundles are actually caddisfly cocoons, assembled meticulously by larvae that live in them for protection while they wait to emerge out of the water as winged adults.

They may seem like innocent artisans, crafting intricate homes reminiscent of cathedrals, but caddisfly larvae are actually aggressive cannibals, often mobbing other larvae and eating them when living conditions get tough. A recent study published in Freshwater Science provided some evidence as to what might happen to these vicious animals as climate change completely alters their environments. The results? They get more aggressive and cannibalistic when more of them occupy the same area and when conditions get dryer or food gets low.

At the Nature Conservancy’s Mexican Cut Nature Preserve in the Elk Mountains of Colorado, snowmelt and rain create small ponds of freshwater habitat where caddisflies deposit their eggs. This is where the study took place.

Over the last few years, the researchers noted that there have been significant changes in water across the region. Compared to the last 10 years, snowmelt and rain have fallen by about 50 cm and 12 cm, respectively. This trend is expected to continue as future climate change becomes increasingly problematic.

What effects will this have on life, you may ask? Nature is really complex, so it’s essentially impossible to tell, but we can start by looking at a species in specific habitats and figuring out how that species reacts to change. Some of these reactions are behavioral.

That’s exactly what the researchers did by setting up two experiments. In one, they tested caddisfly behavior as they got packed into smaller and smaller spaces. In the other, they simulated water and food shortages. Through many observations of aggression, cannibalism and mobbing, the researchers concluded that climate change could have a big role in caddisfly behavior.

When ponds of water dry up, they get smaller, forcing caddislfies into packed spaces. The researchers found that caddisflies not only got more aggressive when packed together, they were aggressive for longer periods of time. Although one may expect mobbing and cannibalism would increase, the first experiment didn’t provide enough evidence. In the second experiment, however, mobbing and cannibalism were observed when water was slowly taken out (drying) and food was in short supply.

Let’s say temperatures kept rising and water levels kept decreasing due to climate change. The results of the above two experiments indicate that caddisflies will soon enter a very hostile world. Not only that, but they will be forced to make their intricate cocoons earlier than ever before, which is another result of the observations made in the two experiments. This process, called pupation, takes place when they are big enough, well-fed and ready, but those standards may become far-fetched in a world undergoing climate change.

Diler Haji is a staff writer for The Daily Campus. He can be reached via email at