Detritivorous insects: recycling pros!

Attracted by the dead body of a chipmunk, this fly is getting ready to lay its eggs on it.
Credit: Insectarium de Montréal (Marjolaine Giroux)
Attirée par le corps mort d’un tamia, cette mouche s’apprête à y pondre ses œufs.
  • Attirée par le corps mort d’un tamia, cette mouche s’apprête à y pondre ses œufs.
  • Ce silphe d’Amérique (Necrophila americana) est à la recherche d’une carcasse où il pondra ses œufs. Ses larves se nourrissent des tissus morts de l’animal alors que les adultes mangent les asticots présents sur la dépouille.
  • Photographiées au Costa Rica, ces termites du genre Nasutitermes contribuent de façon significative à la décomposition du bois mort des forêts tropicales.
Detritivorous insects: recycling pros!

Decomposing organisms are essential for the functioning of our ecosystems, because they make the energy and nutrients immobilized in dead matter available to the higher levels of the food chains. Among those organisms, many detritivorous insects that feed on plant residue, carrion or excrement work in concert with bacteria and micro-fungi at recycling that organic matter. Considering the amount of dead matter produced each year, that recovery plays a key role in the productivity of our natural environments. And without the detritivorous insects, the decomposition process would be fundamentally modified and slowed down.

Zero waste!

In the world, more than 100 gigatonnes of terrestrial plants are produced annually. What happens is that close to 90 percent of that plant matter accumulates, once it dies, on the ground or in streams. This plant mass is not lost, however, because numerous insect species use these “remains” at one stage or another in their life cycles. For instance, in the tropics, termites consume between 50 and 100 percent of the dead wood in forests, in addition to dead grass, humus, fungi and the excrement of herbivores. Closer to home, some 20 to 30 percent of all species of forest insects depend directly or indirectly on dead wood. Among those are the larvae of the white-spotted sawyer (Monochamus scutellatus), which, in order to feed, digs deep galleries in trunks. These larvae consume or break up a significant proportion of the wood and allow for the entry of microorganisms, which decompose the nutrients stored in the remaining dead wood and return them to the forest environment. Finally, in streams, the accumulated plant detritus supports populations of detritivorous aquatic insects, including the larvae of mayflies and caddisflies, which in turn support a great diversity of animals by serving as food.

Vanish, carrion and feces!

Carcasses and excrement are transient habitats, of high nutritional value, that are home to complex communities of decomposing organisms. Thus, a number of Coleoptera, including scarab beetles and earth-boring dung beetles, consume and bury the manure of large herbivores. Through their actions, these insects enable the recycling of nitrogen and contribute to the formation of nitrates absorbable by plants. Moreover, according to studies in pastures, the impact of those nutrients’ mobilization by beetles on plant growth compares favorably with that of chemical fertilizers. At the same time, numerous fly species lay their eggs on excrement that serves as food for the maggots. The tunnels dug by these larvae (and also by beetles) accelerate the work of the microorganisms, and consequently the degradation of organic detritus. Without these specialized insects, carrion and fecal matter would decompose much more slowly, leading to the accumulation of organic waste in our living environments.

Despite the major impact of detritivorous insects on the decomposition of organic matter, there are still few studies documenting the effects of the decline in their populations on the environment. But one thing is certain, our wellbeing depends on protecting these highly specialized insects.

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