The use of interconnected hollow artificial rocks to protect and increase the local diversity of invertebrates and other taxa
It is a well-known fact regarding the imminent collapse of invertebrate populations and its devastating consequences for the ecosystem. There are many reasons for such a foreseen looming downfall which has already been set in motion.
One cause is global warming, which not only stresses animals by constraining them to living under a higher temperature range thereby disrupting biological patterns but also brings an increase in forest fires, a destructive fate for terrestrial species.
Another cause is the ever increasing pressure from human habitation taking vital space and resources. To reverse the disappearance of invertebrates, we can plant indigenous plants and create habitat for invertebrates. However, we can even boost the population of invertebrates by creating a manmade habitat designed around their needs.
Two years ago, during a search for invertebrates for a training course on a very dry and hot winter in KwaZulu-Natal, South Africa an idea came about that might be useful to protect and even boost the local invertebrate and small vertebrate diversity of an area. The idea was: what if a rock is hollow? The concept of a hollow rock and how to keep it cool during a hot day spawned many designs for a faux rock structure.
A hollow rock or eco rock facilitates a habitat for several nocturnal invertebrates that require high humidity and low exposure to the sun, such as millipedes, centipedes, crickets, snails, scorpions, spiders, etc. It is also beneficial for small amphibians and reptiles as well.
An eco rock offers a shelter from predators outside the rock and furthermore a steady humid environment, thus avoiding dehydration. Nonetheless, it is also the arena for battles between predators (e.g. a scorpion vs. a centipede) and a place for predators to find prey that are in search of shelter.
It all started with a simple concept of a rock with a cavity inside and one entrance. Later on it was decided to place a pool lined with moss on top, water from the pool moistens the moss which in turn keeps the interior of the faux rock cool.
The eco rocks turned out to be very successful in harboring spiders in the underlying cavity as well as bees, wasps and butterflies on the moss cover on top. They practically offer a service to most animals of the local ecosystem, thus I termed them “eco rocks”.
Underneath of eco rocks showing different cavities for invertebrates to dwell.
A large eco rock visited by Glossy Starlings.
A useful application of the eco rocks would be to use them to protect the local diversity of invertebrate species in a large area prone to bushfires. For that purpose, the eco rocks must have the following properties:
1- The eco rocks must be relatively light in weight to be easily transported to their destination.
2- Local animals must not be able to lift the eco rocks; this can be achieved by interlocking each rock between each other.
3- The eco rocks must be connected between each other in such a way those invertebrates can move from one eco rock to another one without going outside. This will establish an “underground” world that is not limited to the night time but extended during the day as well.
4- The eco rock must be camouflaged in other to avoid human interference/ disturbance from people.
To satisfy those properties above mentioned I propose a simple collection of eco rocks that connect with one another creating a combination of possible eco-rock landscapes. For the construction a mixture of cement and perlite should be used in which the latter renders a very light weight structure and offers some thermal insulation property as well.
There are two types of interconnected eco rocks: one is simple upper surface and underneath with diverse cavities. The other one is with a depressed upper surface to collect water during rain and inside a shallow container to store the water and make it available to invertebrates.
The eco rocks are connected through a male and female outlet. Therefore invertebrates can move from one rock to another one without coming outside.
The eco rocks are made with a combination of Pratliperl (ultra-lightweight, thermally-insulating and fireproof aggregate for plaster screed and concrete only available in South Africa) and cement, rendering a structure quite light and thermo resistant.
Sketch of two types of interconnecting eco rocks showing the different openings
A simple upper surface eco rock showing a male connector (left) and a female connector (right)
Bottom: A water collector eco rock showing the container that goes underneath.
A sketch of a top view depicting the layout of a series of eco rocks. The path for invertebrates is represented by dashed lines.
Example of a small eco rock landscape.