Springtails. Springtails are among the most abundant of all insects. They live in a variety of habitats and are mainly scavengers on decaying vegetation and fungi. All species are small (less than 1/2 cm in length) and very susceptible to desiccation and typically seek a moist environment. A unique tube-like structure (collophore) is located on the underside of the first abdominal segment of most species. The exact function of this organ is unknown, but it likely helps maintain water balance by absorbing moisture from its environment.
They come in a variety of colors and typically live in hidden locations with soil being their most common habitat. Most soil-inhabiting springtails feed on decaying vegetation or fungi, but some feed on a variety of materials such as dead insects, algae, pollen, insect feces, rotting fruit, mushrooms, fruit in contact with the ground and a few are predators. Being soft-bodied and quite susceptible to desiccation, moisture is the most critical factor in their environment.
Under proper conditions, they can attain huge populations. In an average pasture and other similar situations (lawns), there can be upwards of approximately 250 million of these tiny insects per acre. An acre is the approximate size of a football field. This number is only surpassed by mites that reportedly averaged 666 million individuals per acre. These insects can even be found in extreme climates. Springtails (and mites) are one of the few permanent inhabitants of the Antarctic. On bare ground (not covered by snow and ice), these tiny insects can be quite common even in temperatures as low as -85 degrees F. Under these conditions, they commonly seek out dark rocks which absorb enough heat for them to reproduce and survive.
The authors once saw the entire surface of a large swimming pool covered by these tiny insects. Over a long period of time landscapers had piled grass clippings, leaves and other vegetation in a lot next to the pool. This being an ideal habitat, the springtails built up in huge numbers. In hot weather the decaying vegetation dried up forcing the springtails to leave, and many fell into the pool.
Even though springtails are one of the most (perhaps the most) common insects on earth and occasionally feed on ripe fruit, there are very few cases where they reach pest status. This can be explained by their small size and the fact that most fruit is picked green in agriculture. This is not attractive to springtails. They can be encountered in strawberry fields, as ripe fruit is occasionally found in contact with the ground. In addition, they occasionally are nuisance pests in mushroom farms and various landscaping situations. They rarely are nuisance pests in and around homes.
Springtails are named for a forked jumping organ (the furcula) found on the underside of the fourth abdominal segment. The furcula is retracted against the ventral wall of the abdomen and held there in a cocked position by a special catch (the tenaculum) on the third abdominal segment. Releasing the tenaculum causes the furcula to snap down against any substrate and consequently flips the springtail some distance through the air. The furcula is present in all but a few genera and functions as an effective adaptation for avoiding predation.
Immature Collembola are similar in appearance to adults since both forms lack wings. They usually molt 4-5 times before reaching sexual maturity, and along with silverfish continue to molt periodically throughout the rest of their life. This is very rare in the insect world. Unlike most other arthropods, springtails have evolved in a cooler climate. Their abundance in the soil typically increases as temperatures decrease and they develop most rapidly under cool, humid conditions.
The mating behavior of these tiny insects has been studied quite heavily (Oh! the exciting life of entomologists.) Actually, their behavior is quite interesting because the male has no means of transferring his sperm directly to the female. In one common species, as the male approaches the female she more or less ignores his presence. He often will attempt to gain her attention by continuously stroking her with his antennae until she becomes reasonably still. He then deposits a whole ring of semen droplets (spermatophore) around her. Each droplet is placed on the end of a short stem. Up to 50 of these can be produced by a single male. Of course the female once encountering this encirclement of stalked sperm blobs eventually lowers her reproductive opening over one of the blobs.
Males of other species are less organized (and more spontaneous!) in the placement of these globules and place them more or less at random. Because males of these species can produce hundreds per individual, the total number produced must be staggering considering the number of springtails in nature. The sperm does not last, and is not uncommon for males of these species to consume the older unused stalks and sperm. This type of external reproduction is not unique to springtails but is commonly found in other soil inhabiting arthropods such as mites, silverfish, scorpions, millipedes and centipedes.
Booklice. These tiny insects are generally about the size of a period. They can be winged or wingless as adults and possess chewing-type mouthparts. The best known is the light-colored wingless forms that are called booklice.
Winged Booklouse. Image Courtesy S. Thorpe. Public Domain.
These insects commonly feed on book bindings, various stored products, fungi and in bird nests where their food consists of feathers and waste material. Even though these insects commonly are found in libraries and occasionally are of considerable concern as "book-eating pests"' it is quite unlikely that they can cause any discernible damage. This is based on the fact that large numbers are almost never found around books and the insects are too small to damage such items.
Certain booklice are capable of making faint ticking sounds by tapping their abdomens against a resonant support such as a thin piece of paper. This is thought to be associated with their mating communication. This sound is so faint that it can be heard in only the quietest situation. In Old England, this ticking was frequently thought to be a sign of impending death as it frequently was only heard in quiet sickrooms. Therefore, "Deathwatch" became the term used to describe this sound and behavior.
As indicated, some species of booklice feed on fungi. On occasion, thousands of these insects can be found emerging from the walls of one- or two-year-old homes. In this situation, developers typically have used "green" lumber (has a high moisture content) when constructing the houses. Because of moisture, fungi developed in the wall void and this eventually resulted in huge booklice infestations. When the wood dries, the fungi dies, and the booklice seek a more hospitable environment by emerging from the walls. This is a temporary situation and usually ceases in a few days.
Earwigs. This is a relatively small order (about 1000 species worldwide). Earwigs are commonly encountered and easily recognized by the average person. They sometimes are incorrectly referred to as pincher bugs. Their most obvious characteristic is the pair of pincher-like anal cerci on the end of the abdomen. These structures are useful for defense but cannot harm humans. Earwigs can be non-winged or winged with some being capable of flight.
Most earwigs produce two generations per year. The female normally deposits a clutch of 20 to 30 eggs in small cavities in the ground beneath rocks and boards. Most species periodically turn and groom their eggs in order to prevent fungus from developing that eventually could kill them. This is one of the few situations in the insect world where maternal instinct is exhibited. This is not the same as protective human maternal instinct, because the female earwig frequently eats her eggs if she's disturbed.
Exposed Nest of a European Earwig with Female Protecting and Grooming Her Eggs. Image Dr. Kaae.
The most common species of earwig found in California and throughout much of the United States is the European earwig. This species is about ¾" long, uniformly dark brown in color and bears tan colored short wing pads (modified first pair of wings) that cover the thorax and part of the abdomen. This species feeds on a variety of plant and animal matter but prefers the former. Another common species is the desert earwig that is considerably larger than the European earwig, and is multicolored with reds and yellow on the body. Significantly, this species is a predator and is commonly found in crops. A third common species is the ring-legged earwig. This species is dark brown, slightly smaller than the European earwig and wingless as an adult. It feeds primarily on decaying organic matter although as with most earwigs is somewhat omnivorous.
Plant feeding earwigs occasionally become a problem to the backyard grower as they eat holes in vegetables and flowers. If a gardener is not sure what is attacking plants, this usually can be remedied by a close inspection at night (most insects are nocturnal). If the pests are earwigs and pesticides are not desired for control, they can be trapped out of a garden by placing a damp burlap sack flat on the ground. This serves as an ideal daytime hiding place. Once trapped, they can be destroyed by any number of physical means (e.g. step on them).
The name earwig was given these insects in Europe because of the superstition that they crawl into the ears of sleeping people. Actually there have been a few cases in medical records where earwigs have been removed from a human outer ear canal and even up into the nose. Certainly these situations are quite rare and should not be of concern; it probably is associated with the earwigs’ nocturnal feeding habits. After feeding, earwigs typically hide during the day in dark, protected locations. It is conceivable that the ear canal or nostril of a person sleeping on the ground (e.g. camper) could be confused with a hiding place.
Actually, a surprising number of objects (including insects like cockroaches) have been removed from individual’s ears. Our young daughter once complained of an earache for a few days so we took her to the doctor. The doctor looked in her ear and pulled out a small, soggy wad of paper. When she saw it, she asked if she could have it and quickly unrolled it announcing “It used to have a phone number on it.” Apparently one of her friend gave her a phone number and she had nowhere to keep it, so she stuck it in her ear about two weeks earlier. She doesn’t do that anymore!
Many outdoor insects and other arthropods on occasion enter homes. These are referred to in the industry as dooryard pests. Dooryard pests generally enter homes or structures under doors, or other avenues. This is commonly a result of an unsuitable change in their environment. For example, earwigs are generally found outdoors under rocks, leaf litter, and boards that are in contact with the soil. Moisture is critical to their survival. If their environment dries up or their habitat is removed, the insects will leave in search of new homes. In so doing, they may accidentally blunder into the home. Other reasons that may cause arthropods to leave their outdoor habitats include heat,
Thrips. Thrips are tiny insects (usually less that 1/16-inch in length) and are rarely noticed by the untrained eyes. Regardless, they are another one of the most common insects in the world. For example, in one study over 1,500 thrips were recorded from a single rose flower. With thrips each wing is composed of one central vein that is fringed with rows of hair (Thysano=hair in Greek). This type of wing is unique to this group which is the smallest of flying insects. Most insect wings are composed of a number of veins supporting a strong membrane or in some orders the first pair of wings is protective in nature. This standard type of wing would possible be non-functional in such a tiny insect. Large insects don’t have to deal with the thickness of air creating drag as they fly. In the case of thrips, the fine hairs of the wing replace the membrane and apparently eliminate this potential problem.
Common Thrips-Image Compliments of Rob Hille CC BY-SA 4.0.
Most thrips are phytophagous; being so small, they can feed only one cell deep on a plant surface. They scrape away at the plant cell walls and suck up the contents. Regardless of their shallow feeding, a number of thrips species are important pests on plants.
The citrus thrips are a primary pest of citrus. This species feeds on the new growth, buds and fruit of citrus trees. The growth of young trees may be retarded and fruit and leaves may be distorted. This thrips is an especially important pest on navel oranges. When the fruit is about the size of a small pebble, thrips feed on the fruit immediately next to where the stem attaches. Once this fruit matures, the result is a superficial ring-like scarring about 1 ½" in diameter. This scarring only extends one cell deep and in no way affects the meat of the fruit. In many countries of the world, this type of superficial damage is of little concern. However, in the United States, Japan and other highly industrialized countries, the general public prefers unscarred, nearly perfect fruit. Correspondingly, agricultural agencies regulate the quality of fruit that can be sold in the market place. In the United States navel oranges that have the superficial damage caused by the feeding of citrus thrips cannot be sold as fresh fruit. It makes little difference that their feeding is restricted to the rind and has no effect on the nutritional value of the fruit. Consequently, citrus thrips are considered one of the major pests of citrus grown for the fresh fruit market.
Orange with Superficial Scarring of the Peel Due to Thrips Feeding in This Area When the Fruit Was the Size of a Marble. Image Dr. Kaae.
Thrips occasionally bite humans. This normally happens during hot summer days when thrips are attracted to perspiration on the skin. The bite is obviously not severe and feels like a faint pinprick.
Silverfish. The silverfish or bristletails are moderately sized insects that are carrot-shaped, wingless and possess two or three elongated tail-like appendages (anal cerci) on the tip of the abdomens.
Left. Firebrat (Thysanura). IOmage Dr. Kaae. 34Right. Silverfish. Image Courtesy Christian Fischer CC. BY-SA 3.0
Thysanura have chewing type mouthparts. Their bodies typically are covered with scales and some species are silver colored, hence the name silverfish. Because they exhibit ametamorphosis, the nymphs are smaller replicas of the adults. Silverfish are unique in the insect world in that they exhibit an indeterminate number of molts. They may molt 30 or more times as nymphs and many species continue to molt as adults. The firebrat holds the record at 60 for the most molts in the insect world
Silverfish feed chiefly on materials with high sugar or starch content. In homes they feed on book bindings, wallpaper, paste and starched clothing. Their life cycle is quite long and may take two to three years to complete. They are pests in bakeries as well as homes. Firebrats are a motley brown species that exhibit the same food preference and life cycle as silverfish but prefer relatively high temperatures. In homes they may be found around hot water heaters, furnaces or in attics during the summer.