Arachnida (Spiders, Scorpions, Mites, and Ticks)

Arachnida (Spiders, Scorpions, Mites, and Ticks)

(Spiders, scorpions, mites, and ticks)

Number of families 648

Thumbnail description
Highly recognizable and populous eight-legged invertebrates with two body parts (a prosoma and an abdomen), pedipalps, book lungs or tracheae, sometimes poisonous fangs, and generally the ability to produce silk; they are terrestrial chelicerates (invertebrates with pincershaped mouthparts)

Evolution and systematics

Fossil records suggest that arachnids were among the first animals to live on land, switching from water- to air-breathing. The oldest known arachnid fossils date from the Silurian Period, more than 417 million years ago. It is during this period of time that scorpions (order Scorpionida) appear to have left the water for life on land. Many paleontology experts presume that scorpions were the first animals to make the transition from water to land. In fact, the histological resemblance between the gills of king crabs and the lungs of scorpions help to support this hypothesis. However, the subphylum Cheliceraformes, as a whole, spent many millions of years in the water before it became terrestrial. More than 60,000 species of arachnids are described, although many species, especially mites, remain undiscovered or discoveredbut-not-yet-described. Spiders, mites, and ticks constitute the largest and most diverse orders of arachnids. Among the extant species, scorpions are known to have had a long maritime history that continued well after some of them switched to living on land. The marine-living scorpions, at that time, were very large, some up to 3.3 ft (1 m) in length. The harvestmen (daddy longlegs) are also believed to have had a pre-terrestrial history in the sea.

Currently, arachnids constitute the subclass Arachnida, in the phylum Arthropoda. The subclass is divided into 11 distinct orders: Acari (mites, chiggers, and ticks), Amblypygi (tailless whip scorpions), Araneae (spiders), Opiliones (daddy longlegs), Palpigradi (palpigrades), Pseudoscorpiones (false scorpions), Ricinulei (ricinuleids), Schizomida (micro whip scorpions or schizomids), Scorpionida (scorpions), Solpugida (wind scorpions or solifugids), and Uropygi (whip scorpions and vinegaroons). Many scientists now categorize Arachnida at the class level.

Physical characteristics

There are at least 10 features of arachnids that are often used to describe the group, including:

  • carapace may be uniform or in part segmented
  • pedicel may be absent or present
  • sternum may be uniform or segmented
  • opisthosoma may be uniform or segmented
  • chelicerae may contain two or three segments (podomeres)
  • pedipalpi may be pincer-like or leg-like
  • coxae of legs or pedipalpi may or may not contain gnathobases (plate-like anterior expansions)
  • first leg may be used as a leg or like an antenna
  • legs may be of seven segments (podomeres) or may be sub-segmented anywhere
  • coxae may meet and hide the sternum or may be separated

Anatomical features such as two pairs of limbs, the pedipalps and chelicerae, are distinctively present but greatly modified for different uses in various arachnid species.

The 18-segment arachnid body is often protected by sternites below and tergites above, connected by a soft pleural membrane, and is divided into two tagmata: anterior and posterior. The anterior (front) part, called the cephalothorax (or prosoma), contains sense organs, mouthparts, and limbs or appendages in pairs. The cephalothorax is composed of an anterior, unsegmented region called the acron, and six true segments (each bearing a pair of appendages). It accommodates both the head and limbs. A carapace-like shield completely or partially covers the cephalothorax of arachnids. The first pair of limbs (chelicerae) attached in front of the mouth may form pincers or poison fangs, and the second pair (pedipalps) behind the chelicerae may serve as pincers, feelers, or additional legs. The other limb pairs are used for walking. The 12-segment posterior (rear) part of the body, the abdomen (or opisthosoma), contains the genital opening and other structures. The abdomen may be segmented (as in scorpions) or unsegmented (as in most ticks and spiders). Abdominal appendages are either lacking, or modified into special organs such as the spinnerets of spiders and the pectines of scorpions.

Arachnids breathe by means of tracheae (windpipes), book lungs (modified gills), or both. The mouth of arachnids is not readily noticeable from the external surface. They do not possess jaws (mandibles), but instead have cutting or piercing appendages called chelicerae. The open circulatory system distributes blood from the heart to an enlarged blood space by the use of arteries. The heart is a tubular organ located dorsal to the mid-gut, containing various openings so that blood can be returned to the heart. The central nervous system consists of two cerebral ganglia connected to a pair of sub-esophageal ganglia by means of a circum-esophageal linkage (commisure). Arachnids possess a number of sense organs, many related with the outer body covering (cuticle). The most common of these sense organs is the hair-like setae that are sensitive to various stimuli; they are generally located throughout the surface of the body.


Arachnids are found throughout the world from equatorial to polar regions, but reach their most abundant numbers and diversities in very warm to hot, arid and tropical/subtropical regions.


Arachnids are essentially terrestrial animals that are found in nearly every habitat around the world.


Arachnids are terrestrial, except for some mites and a few spiders that can still be found in water. Most arachnids are solitary creatures, other than during mating periods. Even normally sedentary species will roam when in search of a mate. A courtship ritual usually precedes reproduction. A large proportion of their lives are spent in long periods of inactivity, often waiting for prey to stumble upon them. When disturbed by possible danger, they often fall motionless, acting dead, and try to appear nearly invisible to approaching enemies. Regular activities are instinctive by nature, geared primarily toward perpetuating the particular species and activated by external circumstances (such as the general environment and light intensity) and internal adaptations that have been modifying over thousands of years. Some species ambush their prey, while others chase them down. They feed on specialized prey or on many different types of food, depending on species. Arachnids also feed in various ways: as herbivores, scavengers, parasites, cannibals, and carnivores.

Feeding ecology and diet

Arachnids are predaceous, either actively hunting or patiently lying in wait for small animals such as insects. They have various structures that are geared to capturing prey. Some of these features are the segmented, stinging tail of scorpions and the abdominal spinnerets (that allow for the construction of insect traps, or webs) of spiders. Since they do not have the ability to masticate (chew) their food with their mouthparts, they are generally able only to feed on the fluids of their prey. After piercing the prey’s body wall with their chelicerae, arachnids will either ingest the fluid contents or digest the tissues externally with enzyme-containing secretions that are ejected from the mid-gut (as with spiders) or the salivary glands (as with ticks and mites). A powerful suctorial pharynx draws the fluid up through the pre-oral food canal and delivers it into the mid-gut. Gaseous exchange occurs in a variety of ways. Respiratory gases may enter and leave the body through specialized structures (either lungbooks or spiracles) or may diffuse through the cuticle (as in some mites and larval ticks).

Reproductive biology

During mating, a variety of complex behavior patterns are normally observed. Generally, the reproductive organs are

contained in the abdomen and open ventrally on the second abdominal somite. Male sex organs may consist of one diffuse testis or one or two compact testes. The spermatozoa produced are conveyed to a median gonopore through one or two excretory ducts (vasa deferentia). Insemination into the female may come from the male gonopore in a liquid medium (as in spiders) or may be contained in packages called spermatophores (as in ticks and scorpions). An intermittent organ or penis may or may not be present to direct the spermatozoa into the female during mating. Females possess a single or paired ovary, which may be either compact or diffuse and one or two oviducts may lead to the median gonopore. Eggs may be laid underground, in the shelter of a stone, under tree bark, enclosed in a cocoon, or other variations of these methods and structures. Females usually guard eggs or young, which are often born live and as miniatures of the adult with regard to appearance. Eggs may number from one to more than 1,000 in a single brood.

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Conservation status

As a group, arachnids are considered abundant all over the world. Some species are diminished in numbers, even considered rare or endangered, because of internal circumstances (such as limitations of habitat) or external circumstances (such as human activities). The 2002 IUCN Red List includes 18 arachnid species: one as Endangered; nine as Vulnerable; one as Lower Risk/Near Threatened; and seven as Data Deficient.

Significance to humans

Most arachnids are harmless and contribute to the give and take of nature by controlling the populations of the insects they prey on or the plants, reptiles, birds, or mammals that serve as their hosts. A few species are serious agricultural pests. The bites of some spiders, such as the black widow spider and the brown recluse spider, and the stings of a few species of scorpions are dangerously poisonous to humans.

Spiders That Burrow

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Although spiders might not be the creatures that first come to mind when you think of burrowing, several types of the arthropods regularly engage in the digging behavior. Wolf spiders and trapdoor spiders are just two examples of arachnids that spend much of their time in the ground.

Sit-and-Wait Predators

Many spiders that burrow are sit-and-wait predators, meaning they wait for prey to move past the entrances of their burrows rather than actively pursuing them. When they notice that targeted prey animals are nearby, they launch surprise attacks on them. Arachnids such as trapdoor spiders (family Ctenizidae), tarantulas (family Theraphosidae) and wolf spiders (family Lycosidae) all remain in their burrows while patiently awaiting their next meals getting closer. Mouse spiders (family Actinopodidae) usually sit and wait, although they sometimes venture out to search for prey.

Burrow-Borrowing Spiders

While some burrowing spiders such as tarantulas are adept at digging their own holes, others are not. Long-legged cellar spiders (family Pholcidae) spend time in burrows, but they let other animals do the dirty work for them, especially rodents. Desert grass spiders (Agelenopsis aperta), on the other hand, are frequently found close to burrows made by rodents, but mostly because their webs, which are usually located in high grass, dangle down into them.

Nocturnal Burrowers

Spiders exist both in diurnal and nocturnal varieties. Some burrowing spiders prefer to wait for unsuspecting prey — from the comfort of their burrows — at night. Tarantulas are nocturnal creatures and are part of this category. Trapdoor spiders too are nocturnal. Burrowing wolf spiders, on the other hand, tend to be diurnal.

Spiders That Use Silk to Catch Prey

Burrowing spiders often seize their desired prey with the use of handy silk. Trapdoor spiders, for one, fit this description. These arachnids’ burrows are topped with the «trap doors» of their naming. They use their own silk to produce these doors, which they handily conceal with dirt. One edge of the door is attached, while the spider securely grabs the other. When prey animals approach, these fast-acting spiders immediately force their bodies upward to retrieve them. Funnel web spiders (genus Hadronyche) also employ silk to capture prey. They stick threads of silk out from the entry points of their burrows. When prey animals make physical contact with the threads — and therefore trip on them — funnel web spiders immediately swoop in for dinnertime.

How To Keep Your Yard Free Of Ticks

Although ticks tend to prefer moist habitats such as the vegetation near water, the undergrowth in the woods or at the edge of the forest, and meadows with tall grass, unfortunately, they are also found in increasing numbers in our gardens.

How Do Ticks Get Into My Yard?

Ticks can crawl around, even very slowly, but this also leads to their spreading over time. Ticks mainly spread by hitching a ride on a host, they don’t care whether it is a wild or a domestic animal.

Most responsible for spreading ticks are birds, deer, mice, rats, rabbits, squirrels, foxes, martens, possums or even raccoons. And as all these animals are increasingly entering urbanized areas, they bring along with them unwanted garden guests. But not to forget our pet dogs and cats that roam the outdoors, they pick up ticks and spread them too.

Unfortunately, mice and many rodents may be a host to pathogens, such as Lyme disease, Tularemia, Rocky Mountain spotted fever, Ehrlichiosis, and many others. By biting and sucking the blood of an infected host, the ticks also become infected with the pathogens, and when biting a human next pass the illness on.

How To Check My Yard For Ticks

You may have picked up a tick already in your garden, or maybe your pet has, in fact, most ticks are picked up in urban areas and our immediate surroundings. If you suspect ticks in your yard, you can do a simple test to check whether the nasty bloodsuckers are on your property. The method is called Tick Dragging, researchers use the same method to collect and study tick populations in the wild.

Simply get a white cloth or sheet and slowly pull it through your yard and over vegetation and hiding places where you suspect ticks may be hiding. The little creaturs will cling onto the cloth. Examine the black or brown spots on the fabric with the help of a magnifying glass. Ticks can clearly be identified as arachnids on their eight legs.

Where do ticks hide?

Ticks feel particularly comfortable in shady, humid surroundings amongst grasses and shrubbery. Dense ground cover and undergrowth near walls and fences are areas where mice and rodents travel. Such places can turn into tick hotspots. Other places where ticks lurk may be:

  • between piles of wood
  • between and along stone walls
  • along fences and walls
  • near garden huts and tool sheds
  • around bird feeding places, or around chicken coops
  • compost heap and garden waste
  • tall grass, dense flower beds, and perennial gardens

What can you do against ticks in the garden?

It is really hard to drive ticks completely out of your garden, but you can reduce their number significantly, by depriving them of their hiding places. Ticks love moist and warm places that offer them good protection against excessive heat in summer and a safe place to spend the cold winter months. To reduce tick populations in your garden clean up or remove all those places and make it as unfriendly as possible.

How to Get Rid Of Ticks In Your Yard

In addition to some enemies such as fungi, roundworms, small wasps, and various bird species, ticks have another big enemy: a clean, dry environment without hiding places.

  • Keep your garden clean and allow the sunlight to reach the ground.
  • Regularly trim tall grass, weeds, and shrubbery
  • Prune perennials and trees two to three times a year.
  • The growth in the shade under trees also offers great hiding for ticks. Regularly thin out vegetation under the tree
  • Rake up the leaves and put them on the compost. Large piles of leaves on the ground provide a moist environment and pleasant conditions for ticks.
  • Remove excessive moss from your lawn, use a scarifier to make the lawn more airy and uncomfortable for ticks.
  • Limit plant growth. Prune perennials and trees regularly remove dead, rotting and overgrown vegetation.
  • Avoid overgrowing grass and remove climbing plants and other overgrown bushy plants.
  • Mow the lawn regularly. By keeping the lawn low, sunlight reaches the ground and there is less moisture and shade. Short grass also deprives ticks of the ability to crawl up and wait for a host.
  • Keep the area around birdbaths and bird feeds clean and keep the vegetation low.
  • Store your firewood neatly stacked and in a dry place. Piles of wood can provide ideal dark and moist hidings. A dry stack of wood is uncomfortable for ticks and makes your firewood is dry and doesn’t rot.

Cultivate plants that have tick repelling properties

Plants are food for many insects. To fend of nibbling insects many plants produce chemicals and essential oils.
Many of these essential oils work effectively as natural pesticides or repellents and keep insects, mites, and arachnids away.

What Kills Ticks In The Yard

Using commercial insecticides will kill ticks, but also all beneficial insects. Insecticides should be used with care and only applied locally in tick-infested areas. You can use the following natural methods to get rid of ticks in yard and garden.

Spray Your Yard With Beneficial Nematodes

Nematodes are tiny worms that are almost invisible to the naked eye, they occur naturally in soil throughout the world. They are either free-living or parasitic – means they need a host to feed on. Each species of nematodes specifically affects one particular or a small group of similar hosts.

The Beneficial nematodes that are used in gardening are harmless to humans or animals and do not harm aquatic life, birds, reptiles or amphibians either.

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Apply Diatomaceous Earth to Tick Prone Areas

Diatomaceous earth also called Diatomite, consists of the powdered fossil shells of extinct algae (diatoms). The consistency is powdery, the colors range from pure white to gray-brown.

Diatomaceous earth has the ability and power to kill all bugs: razor-sharp edges, invisible to our eyes, tear open the protective “chitin shell” of creeping insects and fleas and ticks. Pests are literally dried out.

Diatomite has no side effects for humans and animals.

Home Tick Spray For Yard And Garden

A tick spray for yard and garden that is made from naturally occurring substances will be less harmful to the environment. If you fear unwanted side effects to your family and your pets, it may be safer to use around the house. The following recipe is based on natural ingredients to fight the pests without toxins:

  • Boil a quart of water in a pot
  • Slice some lemons, put them into the pot
  • Add peppermint leaves or sage, or basil or garlic
  • Let it boil for an hour
  • You may add a few drops of essential oils such as geranium of lavender oil enhance the effect
  • Let it cool down
  • Fill into a pressure sprayer
  • Spray all dark, damp, places where ticks may hide regularly

Personal Tick Protection When Outdoors

There is no 100% protection against tick bites, just as there is none against mosquito bites or catching the flu. However, you can reduce the risk by a few protective measures. The risk of a tick bite can be minimized with just a few rules of precaution:

Avoid their hiding places: Ticks lurk in tall grass, shrubs, and undergrowth. If you don’t have to foray through tall grass and undergrowth, stay away from it.

Wear the right clothing: Ticks can only bite directly into the skin, they cannot bite through clothing. Long-sleeved clothes also offer effective tick protection. Wear closed shoes and long trousers, put your pants leg in your socks. Light clothing makes it easier to spot the crawling animals.

Use tick protection: Using good repellants that contain DEET or Picaridin provides effective protection against ticks for a couple of hours. Before using such synthetic repellents, read instructions and use it as recommended.

Natural insect repellents that contain essential oils can also provide protection, but they are not as effective as the known synthetic repellents. Certain factors such as high temperatures, wind or excessive sweating may reduce the effectiveness of topical tick protection.

Have a tick removal tool ready: You should remove a tick as soon as you notice that you are bitten by one. The faster you remove a tick, the lower the risk that it will transmit an illness.

After being outdoors in nature, you should check your clothes and body thoroughly for ticks. Ticks may bite everywhere, but prefer sites where the skin is thin and soft. Check under armpits, in the neck area, in the back of the knees and in the groin area.

Natural Resources Conservation Service

Soil Biology Primer Chapters

Soil Arthropods

By Andrew R. Moldenke, Oregon State University


Many bugs, known as arthropods, make their home in the soil. They get their name from their jointed (arthros) legs (podos). Arthropods are invertebrates, that is, they have no backbone, and rely instead on an external covering called an exoskeleton.

The 200 species of mites in this microscope view were extracted from one square foot of the top two inches of forest litter and soil. Mites are poorly studied, but enormously significant for nutrient release in the soil.

Credit: Val Behan-Pelletier, Agriculture and Agri-Food Canada. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Arthropods range in size from microscopic to several inches in length. They include insects, such as springtails, beetles, and ants; crustaceans such as sowbugs; arachnids such as spiders and mites; myriapods, such as centipedes and millipedes; and scorpions.

Nearly every soil is home to many different arthropod species. Certain row-crop soils contain several dozen species of arthropods in a square mile. Several thousand different species may live in a square mile of forest soil.

Arthropods can be grouped as shredders, predators, herbivores, and fungal-feeders, based on their functions in soil. Most soil-dwelling arthropods eat fungi, worms, or other arthropods. Root-feeders and dead-plant shredders are less abundant. As they feed, arthropods aerate and mix the soil, regulate the population size of other soil organisms, and shred organic material.


Many large arthropods frequently seen on the soil surface are shredders. Shredders chew up dead plant matter as they eat bacteria and fungi on the surface of the plant matter. The most abundant shredders are millipedes and sowbugs, as well as termites, certain mites, and roaches. In agricultural soils, shredders can become pests by feeding on live roots if sufficient dead plant material is not present.

Millipedes are also called Diplopods because they possess two pairs of legs on each body segment. They are generally harmless to people, but most millipedes protect themselves from predators by spraying an offensive odor from their skunk glands. This desert-dwelling giant millipede is about 8 inches long.
Orthoporus ornatus.

Credit: David B. Richman, New Mexico State University, Las Cruces. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Sowbugs are relatives of crabs and lobsters. Their powerful mouth-parts are used to fragment plant residue and leaf litter.

Credit: Gerhard Eisenbeis and Wilfried Wichard. 1987. Atlas on the Biology of Soil Arthropods. Springer-Verlag, New York. P. 111. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.


Predators and micropredators can be either generalists, feeding on many different prey types, or specialists, hunting only a single prey type. Predators include centipedes, spiders, ground-beetles, scorpions, skunk-spiders, pseudoscorpions, ants, and some mites. Many predators eat crop pests, and some, such as beetles and parasitic wasps, have been developed for use as commercial biocontrols.

This 1/8 of an inch long spider lives near the soil surface where it attacks other soil arthropods. The spider’s eyes are on the tip of the projection above its head.
Walckenaera acuminata.

Credit: Gerhard Eisenbeis and Wilfried Wichard. 1987. Atlas on the Biology of Soil Arthropods. Springer-Verlag, New York. P. 23. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

The wolf-spider wanders around as a solitary hunter. The mother wolf-spider carries her young to water and feeds them by regurgitation until they are ready to hunt on their own.

Credit: Trygve Steen, Portland State University, Portland, Oregon. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

The pseudoscorpion looks like a baby scorpion, except it has no tail. It produces venom from glandsin its claws and silk from its mouth parts. It lives in the soil and leaf litter of grasslands, forests, deserts and croplands. Some hitchhike under the wings of beetles.

Credit: David B. Richman, New Mexico State University, Las Cruces. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Long, slim centipedes crawl through spaces in the soil preying on earthworms and other soft-skinned animals. Centipede species with longer legs are familiar around homes and in leaf litter.

Credit: No. 40 from Soil Microbiology and Biochemistry Slide Set. 1976. J.P. Martin, et al., eds. SSSA, Madison, WI. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Predatory mites prey on nematodes, springtails, other mites, and the larvae of insects. This mite is 1/25 of an inch (1mm) long. Pergamasus sp.

Credit: Gerhard Eisenbeis and Wilfried Wichard. 1987. Atlas on the Biology of Soil Arthropods. Springer-Verlag, New York. P. 83. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

The powerful mouthparts on the tiger beetle (a carabid beetle) make it a swift and deadly ground-surface predator. Many species of carabid beetles are common in cropland.

Credit: Cicindela campestris. D.I. McEwan/Aguila Wildlife Images. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Rugose harvester ants are scavengers rather than predators. They eat dead insects and gather seeds in grasslands and deserts where they burrow 10 feet into the ground. Their sting is 100 times more powerful than a fire ant sting. Pogonomyrmex rugosus.

Credit: David B. Richman, New Mexico State University, Las Cruces. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.


Numerous root-feeding insects, such as cicadas, mole-crickets, and anthomyiid flies (root-maggots), live part of all of their life in the soil. Some herbivores, including rootworms and symphylans, can be crop pests where they occur in large numbers, feeding on roots or other plant parts.

The symphylan, a relative of the centipede, feeds on plant roots and can become a major crop pest if its population is not controlled by other organisms.

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Credit: Ken Gray Collection, Department of Entomology, Oregon State University, Corvallis. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Fungal Feeders

Arthropods that graze on fungi (and to some extent bacteria) include most springtails, some mites, and silverfish. They scrape and consume bacteria and fungi off root surfaces. A large fraction of the nutrients available to plants is a result of microbial-grazing and nutrient release by fauna.

This pale-colored and blind springtail is typical of fungal-feeding springtails that live deep in the surface layer of natural and agricultural soils throughout the world.

Credit: Andrew R. Moldenke, Oregon State University, Corvallis. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

Oribatid turtle-mites are among the most numerous of the micro-arthropods. This millimeter-long species feeds on fungi. Euzetes globulus.

Credit: Gerhard Eisenbeis and Wilfried Wichard. 1987. Atlas on the Biology of Soil Arthropods. Springer-Verlag, New York. P. 103. Please contact the Soil and Water Conservation Society at [email protected] for assistance with copyrighted (credited) images.

What Is In Your Soil?

If you would like to see what kind of organisms are in your soil, you can easily make a pitfall trap to catch large arthropods, and a Burlese funnel to catch small arthropods.

Make a pitfall trap by sinking a pint- or quart-sized container (such as a yogurt cup) into the ground so the rim is level with the soil surface. If desired, fashion a roof over the cup to keep the rain out, and add 1/2 of an inch of non-hazardous antifreeze to the cup to preserve the creatures and prevent them from eating one another. Leave in place for a week and wait for soil organisms to fall into the trap.

To make a Burlese funnel, set a piece of 1/4 inch rigid wire screen in the bottom of a funnel to support the soil. (A funnel can be made by cutting the bottom off a plastic soda bottle.) Half fill the funnel with soil, and suspend it over a cup with a bit of anti-freeze or ethyl alcohol in the bottom as a preservative.

Suspend a light bulb about 4 inches over the soil to drive the organisms out of the soil and into the cup. Leave the light bulb on for about 3 days to dry out the soil. Then pour the alcohol into a shallow dish and use a magnifying glass to examine the organisms.

What Do Arthropods Do?

Although the plant feeders can become pests, most arthropods perform beneficial functions in the soil-plant system.

Shred organic material. Arthropods increase the surface area accessible to microbial attack by shredding dead plant residue and burrowing into coarse woody debris. Without shredders, a bacterium in leaf litter would be like a person in a pantry without a can-opener – eating would be a very slow process. The shredders act like can-openers and greatly increase the rate of decomposition. Arthropods ingest decaying plant material to eat the bacteria and fungi on the surface of the organic material.

Stimulate microbial activity. As arthropods graze on bacteria and fungi, they stimulate the growth of mycorrhizae and other fungi, and the decomposition of organic matter. If grazer populations get too dense the opposite effect can occur – populations of bacteria and fungi will decline. Predatory arthropods are important to keep grazer populations under control and to prevent them from over-grazing microbes.

Mix microbes with their food. From a bacterium’s point-of-view, just a fraction of a millimeter is infinitely far away. Bacteria have limited mobility in soil and a competitor is likely to be closer to a nutrient treasure. Arthropods help out by distributing nutrients through the soil, and by carrying bacteria on their exoskeleton and through their digestive system. By more thoroughly mixing microbes with their food, arthropods enhance organic matter decomposition.

Mineralize plant nutrients. As they graze, arthropods mineralize some of the nutrients in bacteria and fungi, and excrete nutrients in plant-available forms.

Enhance soil aggregation. In most forested and grassland soils, every particle in the upper several inches of soil has been through the gut of numerous soil fauna. Each time soil passes through another arthropod or earthworm, it is thoroughly mixed with organic matter and mucus and deposited as fecal pellets. Fecal pellets are a highly concentrated nutrient resource, and are a mixture of the organic and inorganic substances required for growth of bacteria and fungi. In many soils, aggregates between 1/10,000 and 1/10 of an inch (0.0025mm and 2.5mm) are actually fecal pellets.

Burrow. Relatively few arthropod species burrow through the soil. Yet, within any soil community, burrowing arthropods and earthworms exert an enormous influence on the composition of the total fauna by shaping habitat. Burrowing changes the physical properties of soil, including porosity, water-infiltration rate, and bulk density.

Stimulate the succession of species. A dizzying array of natural bio-organic chemicals permeates the soil. Complete digestion of these chemicals requires a series of many types of bacteria, fungi, and other organisms with different enzymes. At any time, only a small subset of species is metabolically active – only those capable of using the resources currently available. Soil arthropods consume the dominant organisms and permit other species to move in and take their place, thus facilitating the progressive breakdown of soil organic matter.

Control pests. Some arthropods can be damaging to crop yields, but many others that are present in all soils eat or compete with various root- and foliage-feeders. Some (the specialists) feed on only a single type of prey species. Other arthropods (the generalists), such as many species of centipedes, spiders, ground-beetles, rove-beetles, and gamasid mites, feed on a broad range of prey. Where a healthy population of generalist predators is present, they will be available to deal with a variety of pest outbreaks. A population of predators can only be maintained between pest outbreaks if there is a constant source of non-pest prey to eat. That is, there must be a healthy and diverse food web.

A fundamental dilemma in pest control is that tillage and insecticide application have enormous effects on non- target species in the food web. Intense land use (especially monoculture, tillage, and pesticides) depletes soil diversity. As total soil diversity declines, predator populations drop sharply and the possibility for subsequent pest outbreaks increases.

Where Do Arthropods Live?

The abundance and diversity of soil fauna diminishes significantly with soil depth. The great majority of all soil species are confined to the top three inches. Most of these creatures have limited mobility, and are probably capable of “cryptobiosis,” a state of “suspended animation” that helps them survive extremes of temperature, wetness, or dryness that would otherwise be lethal.

As a general rule, larger species are active on the soil surface, seeking temporary refuge under vegetation, plant residue, wood, or rocks. Many of these arthropods commute daily to forage within herbaceous vegetation above, or even high in the canopy of trees. (For instance, one of these tree-climbers is the caterpillar-searcher used by foresters to control gypsy moth). Some large species capable of true burrowing live within the deeper layers of the soil.

Below about two inches in the soil, fauna are generally small – 1/250 to 1/10 of an inch. (Twenty-five of the smallest of these would fit in a period on this page.) These species are usually blind and lack prominent coloration. They are capable of squeezing through minute pore spaces and along root channels. Sub-surface soil dwellers are associated primarily with the rhizosphere (the soil volume immediately adjacent to roots).

Abundance of Arthropods

A single square yard of soil will contain 500 to 200,000 individual arthropods, depending upon the soil type, plant community, and management system. Despite these large numbers, the biomass of arthropods in soil is far less than that of protozoa and nematodes.

In most environments, the most abundant soil dwellers are springtails and mites, though ants and termites predominate in certain situations, especially in desert and tropical soils. The largest number of arthropods are in natural plant communities with few earthworms (such as conifer forests). Natural communities with numerous earthworms (such as grassland soils) have the fewest arthropods. Apparently, earthworms out-compete arthropods, perhaps by excessively reworking their habitat or eating them incidentally. However, within pastures and farm lands arthropod numbers and diversity are generally thought to increase as earthworm populations rise. Burrowing earthworms probably create habitat space for arthropods in agricultural soils.

Bug Biography: Springtails

Springtails are the most abundant arthropods in many agricultural and rangeland soils. populations of tens of thousands per square yard are frequent. When foraging, springtails walk with 3 pairs of legs like most insects, and hold their tail tightly tucked under the belly. If attacked by a predator, body fluid rushes into the tail base, forcing the tail to slam down and catapult the springtail as much as a yard away. Springtails have been shown to be beneficial to crop plants by releasing nutrients and by feeding upon diseases caused by fungi.

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