What a waste! How invertebrates help to tidy up.

What a waste! How invertebrates help to tidy up.

Green veined White and Small White butterflies on a dung heap (c) Kate Nightingale

In the fifth of a series of Action for Insects blogs, Leicestershire and Rutland Wildlife Trust volunteer and amateur entomologist Kate Nightingale explains how invertebrates help clean up dead vegetation, animal carcasses and dung.

As winter gets underway and we complain about the mud and the muck, consider how much worse things could be without nature’s waste recyclers.

Every ecosystem has an ‘energy cycle’; energy in the form of nutrients and minerals flows from one level in the food chain to the next.  Plants and algae use solar energy to manufacture their food via photosynthesis; plants and algae are then eaten by herbivores; herbivores are eaten by carnivores, and larger carnivores eat the smaller ones.  These feeding stages are called ‘trophic levels’ and couldn’t function without efficient decomposition and recycling of waste products.

Decomposition can be assisted by mammals, birds, insects, molluscs, millipedes, woodlice, earthworms, fungi, moulds, parasites and bacteria.   The initial stage of decomposition may start when a dead leaf is colonised by mould and fungi,  or when a rabbit carcass is scavenged by a Carrion Crow, enabling flies and beetles to access the nutrients within.   

The final stage of decomposition involves the disintegration of organic matter at a chemical level, so that only the component molecules remain. These molecules are then absorbed by plants and algae… and so the cycle continues.

Dung is an important source of nutrients for many insects, and even butterflies are attracted to its salts and minerals, but some species would be completely unable to survive without dung.  Adults of the Noon Fly (Mesembrina meridiana) take nectar and pollen from a variety of flowering plants, but the eggs and larvae develop and feed in cow and horse dung; somewhat unusually for a hoverfly species, the larvae of Rhingia rostrata  rely on deer or badger dung.  A dung beetle called Sphaeridium lunatum can spend its whole life in a cowpat!

The flies commonly known as greenbottles and blowflies (members of the Calliphoridae family) are often found in on around dung but the larvae also eat carrion. The ‘sexton’ or ‘burying’ beetles such as Nicrophorus vespilloides are specifically adapted to living and breeding in carrion and use their powerful legs to bury dead and decaying animals, such as mice and small birds. 

Some creatures are ‘secondary feeders’ in the decomposition process, eating organisms such as the flies, beetles, fungi, mould and bacteria that consume rotting materials. Wasps attracted to carrion will also attack blowflies and their larvae, performing a valuable pest control service. 

In many cases, the invertebrates that colonise and decompose a carcass do so in very predictable ways, arriving in sequential waves that are characteristic of their species. Identifying them and understanding the development of their egg, larval and pupal stages is the foundation of forensic entomology, which aids criminal investigations including those relating to the poaching of wild and endangered animals.    

Rose chafer beetle

Rose Chafer Beetle (c) Kate Nightingale

Putting aside the carcasses and dung for a moment (please!)… There are various insects that help to recycle dead and decaying vegetation. 

The larvae of the Rose Chafer beetle (Cetonia aurata) can be found in organic matter and break down compost and decaying wood; the pupae hibernate in rotting wood or soil, emerging as colourful adults the following spring.  

A significant number of  beetle species consume wood fibres or tunnel in wood to create chambers in which to lay eggs, but some just feed upon the other organisms that need dead wood, such as mosses and fungi. Despite being a hugely important habitat, dead wood is often considered undesirable and is ‘tidied’ up; standing dead trees are chopped down and fallen branches are chipped, burned or cut into logs, which then dry out, depriving invertebrates of essential moisture. 

Longhorn beetle

Longhorn beetle (c) Kate Nightingale

The longhorn beetle Rhagium mordax can be seen on sunny days taking pollen from umbelliferous plants, but females need to lay eggs in the soft and rotten wood of broadleaved trees, in standing or fallen timber, and in old stumps with cracks and crevices.  The larvae can take up to three years to develop so are particularly susceptible to human interference.

Decomposition is a vital and finely-balanced process to preserve nutrients within an ecosystem and aid biodiversity, but it also ensures that humans are not overwhelmed by the massive amount of organic waste that Mother Nature produces each year!

Help insects at home and in your garden