Investigation of Soil Dwelling Invertebrates

Sara Trombetti
Cicely Williams

Ecology
Dr. Tietjen
December 9, 1999

Not many people know about the diverse world of insects that lie under our feet. To get a better understanding of this diverse world we set up a simple experiment to investigate. What we found was amazing. Soil dwelling invertebrates are a vital link in the food chain as decomposers. Without these insects many take for granted nature would have no way of recycling organic material on its own. The technique we used for capture was a Berlese funnel. Once the insects were captured and preserved a little detective work and some high powered microscopes led us to identify our finds and make a few interesting conclusions.

Materials used for experiment

• Berelese funnel
• Ethyl Alcohol
• 40 watt bulb
• Soil, compost, and leaf litter
• Tweezers
• Dissecting microscope
• Microscope
• Slides
• Funnel paper
• Collecting dish
• Kwik key to soil dwelling invertebrates

Procedure/Techniques
The first step to making a good collection is to determine prime sites where insects inhabit. Although insects inhabit just about every inch of this globe a few of the best spots are leaf litter, soil, mulch, and compost. These are the spots that we decided to use for our experiment. The leaf litter and soil mulch was complements of Bonaventure hall and Maryanne Trombetti of Henry County generously donated the compost. From each site a funnel of litter was collected. The Berelese funnel was set up with a collection jar under the funnel separated by a small screen. The funnel was placed under a 40watt bulb and allowed to sit for two days. The bulb evaporated the moisture form the top of the funnel and as the moisture level drops the insects in the soil will travel down with it. Eventually they will fall trough the screen and be collected in the ethyl alcohol.

The next step is to identify the insects collected. How we did this was to run the ethyl alcohol through some filter paper to trap all the insects. The insects on the funnel paper were allowed to dry and then identified using the two microscopes and the Kwik key for soil dwelling invertebrates. The key distinguishes the insects based on number of legs, if there are wings present, shape of the body, eye types etc. The results were then recorded.

Observations

After looking at our results we decided to do a little research on the certain invertebrates that we found. Below is some of the information we found.

Ants, family Formicidae, are a dominant component in terrestrial ecosystems where they actively compete with other invertebrate taxa for microhabitat and food resources. Ants recycle nutrients (Greenslade and Greenslade 1984a); and are important predators and competitors of other invertebrates. Ants also have a major influence on soil structure as a result of their nesting activities (de Bruyn and Conacher 1990) with some genera such as Iridomyrmex transporting soil particles to the surface from as far down as 10 metres as they expand underground galleries throughout the life of the colony. The diversity and abundance of the formicidae in Australia impacts upon the distribution of other invertebrate species in terrestrial environments. Ants are found in numerous habitats such as soil, under stones, hollow branches and numerous cryptic species inhabit forest leaf litter. The formicidae have a unique ability in exploiting habitat resources and provide an ideal assessment method for environmental monitoring.

Mites (Acari or Acarina) are the most diverse and abundant of all arachnids, but because of their small size (usually less than a millimeter in length) we rarely see them. The ticks are an exception, in that they are usually big enough to see, especially when they are filled with blood. Mites are also among the oldest of all terrestrial animals, with fossils known from the early Devonian, nearly 400 million years ago (Norton et al. 1988, Kethley et al. 1989). Three major lineages are currently recognised: Opilioacariformes, Acariformes and Parasitiformes (Krantz 1978, Johnston 1982, Evans 1992). About 45,000 species of mites have been described - a small fraction (perhaps 5%) of the number of species estimated to be alive today. Mites are truly ubiquitous. They have successfully colonized nearly every known terrestrial, marine, and fresh water habitat including polar and alpine extremes, tropical lowlands and desert barrens, surface and mineral soils to depths of 10 meters, cold and thermal surface springs and subterranean waters with temperatures as high as 50C, all types of streams, ponds and lakes, and sea waters of continental shelves and deep sea trenches to depths of 5000 meters. Some idea of mite abundance and diversity can be gained from analysis of one square meter of mixed temperate hardwood or boreal coniferous litter, which may harbour upwards from one million mites representing 200 species in at least 50 families. Within this complex matrix of decomposing plant matter, mites help to regulate microbial processes directly by feeding on detritus and microbes, and indirectly by predation on other microfauna.

None of these mites exceed a centimeter in length, and the vast majority grow to less than a millimeter, yet they often have a major impact on their hosts.

Spiders are arachnids, a group of arthropods that also includes scorpions, harvestmen, mites, and ticks. Approximately 3,000 species occur in North America.

Spiders, like insects (another group of arthropods), have jointed legs and a hard external or outer skeleton. Spiders have four pair of legs, with a body divided into two regions (cephalothorax and abdomen), while insects have three pair of legs and the body divided into three regions: head, thorax, and abdomen. Spiders have no wings or antennae, but have enlarged, sharply pointed jaws called fangs (chelicerae). All spiders are predators. They feed on a wide variety of insects and other soft-bodied invertebrate animals.

Order Isoptera consists of the notorious insect eaters of wood: the termites. There are around 2200 species living mostly at the equator, but generally found worldwide, except in arctic conditions. 41 of the species are resident in North America. Termites are palid, often white, and have biting mouth parts. Their light color has earned them the name "white ants," although there are many dissimilarities between termites and ants.Termites are social insects, meaning they like to live with each other Termites' colonies range in size from about 100 to over seven million! Like most social insects, the termites also have a complex hierarchy within their colonies. The main types of termites found in a colony include the king, queen and young reproductives who are mainly responsible for reproduction, soldiers to protect the colony and the workers who are generally wingless and blind. Each termite has a small, unicellular protozoan living inside of it that enable it to digest wood and other food. Without this symbiont, termites would not be the pests that they are today. The small protists can break down the main substance present in most plants. Even though the termites plague the human civilization, they are imperative to the natural process of decomposition in nature. Termites can help to replenish the soil and get rid of fallen trees and leaf debris. These protozoa are present in in all termites except one family which has evolved a symbiotic relationship with bacteria and fungi.

Coleoptera is the largest of all the insect orders. There are over 300,000 different species known to scientists worldwide, and more are being discovered rapidly. From the most miniscule beetles that are barely visible to humans to the Goliath beetles in Africa the size of a human hand, there are many that can be found anywhere. More information will be provided soon. The term Coleoptera means "shield-winged" for the hard coating on their outside pair of wings. Beetles can live in almost any habitat, from the desert to lakes. Beetles feed on plants or dried grain products, and are commonly regarded as form and garden pests. Many beetles, however, are beneficiary. The lady-bird beetle, commonly referred to as the lady bug, feeds on aphids. Aphids eat crops even faster than beetles, and are almost microscopic. Farmers often buy galons of lady-bird beetles for their crops or garden to keep the aphids from destroying their crop.

Order Dermaptera contains the insects known as the earwigs. There are 1200 species distributed worldwide, except in arctic regions, and 20 species in North America. Earwigs are commonly identified by the presence of two large cerci, or pinchers, on the back of their abdomen used for positioning the wings or protection.

The Scorpion flies are small to medium-sized insects with four long, narrow wings and long antennae. They have chewing mouthparts located at the end of a broad, flat snout, which is two or three times as long as the head is wide. Metamorphosis is complete, the life stages being the egg, larva, pupa, and adult. Scorpion flies are harmless, but they are so named because some of the males have the end of the abdomen enlarged so it looks like the stinger of a scorpion. These insects are found resting on plants that grow along the banks of streams and in damp woods. The larvae are caterpillar-like and live in damp soil. The adults feed on insects, usually after they are dead, although certain species do capture live insects. The adults are sometimes attracted to lights.

Conclusion
In conclusion, not only did we find that this underground world was diverse, but that it was also very complex. Each insect having its own link and purpose in the soils ecosystem. These insects are natural recyclers, they aid in breakdown and decomposition of organic material to allow the soil to utilize nutrients. The insects depend on moisture content to survive this key factor was what allowed for our funnel to work in the collection of insects. This experiment was not only fun, but also very interesting to see the vast and complex world of the soil dwelling insects.