In the past couple of blogs, we learned that oak trees are a keystone species in their habitat, especially for the vast network of relationships between oaks and insects.
Ladybug on oak tree leaf by EMFA16, Getty ImagesLeaf litter and under-bark room for rent, by Wayne S. Grazio, Nov 2013
Insect holes & homes on cork oak, Quercus suber, by Bloor4ik, Getty Images
Oak trees and their surroundings provide shelter and food from leaves, wood, bark, sap, flowers, pollen, and acorns to thousands of species of insects and other invertebrates. Shelter is provided on the tree, inside cavities or other fissures, among the leaf litter, and around the root systems. As oaks age, there are more opportunities for shelter and food, including after branches or the whole tree dies and falls to decay on the forest floor.
Chickadee nest by Jack VandenHeuval, Getty Images
Chickadee eating a caterpillar by Bettina Arrigoni, May 2018
Over 900 caterpillar species have been identified in oak habitats, more than three times the number found in forests dominated by maple trees. Canopy leaves and branches provide shelter and nesting opportunities for dozens of bird species who find a ready source of food within the insect populations. Ninety percent of bird species feed insects, especially caterpillars, to their young. The Carolina Chickadee feeds four to six chicks for 16 days before they fledge. Mealtimes require 400 to 500 caterpillars each day.
Aphids and ants by oday222, Getty Images Pro
Philodromus praedatus spiders live mainly in mature oak trees, by Nikk, May 2016Oak gall by Michael Boubin, Getty Images
Several species of flies and wasps lay their eggs on oak trees, stimulating a growth hormone in the tree to grow a gall, an outgrowth of bark, around the eggs. When the larvae hatch, secretions from the gall feed the larvae, and the gall provides protection to the developing insects. The abundance of insects attracts other invertebrates from higher up on the food chain. Spiders frequently inhabit mature oak trees hunting and feeding on many of the insect species. Aphid colonies are often found on oak trees, but cause little damage to the tree. Aphids feed on the sap from the tree and secrete a sticky, sugary substance called honeydew, a favorite food for ants. The ants protect the aphid colonies, keeping them underground during inclement weather and herding them up the tree in summer to ensure the aphids are well fed to keep producing more honeydew.
Fall webworm, Hyphantria cunea, by Anita Gould, Sep 2015; Polyphemus moth caterpillar, Antheraea polyphemus, by Ed Uthman, Sec 2018; Speckled wood caterpillar, Pararge aegeria, by Dean Morley, May 2013; Linden looper caterpillar, Erannis tillaria, by sankax, Jun 2009
Insects and oak trees have created an environment rich in food for many of its inhabitants. According to Doug Tallamy, a leading entomologist at the University of Delaware, “caterpillars transfer more energy from plants to other animals than any other type of creature.” The loss of habitat for insects puts considerable strain on all other environments, including ones supporting ourselves. Insects do most of the work of pollination, allowing plants to reproduce. They also provide for quick decomposition and the return of nutrients to the soil for growing new plants. Insects are a driving force of the world’s food webs and are necessary for a healthy environment.
Morning in an oak forest by Slatan
There are over 400 species of oaks worldwide, with about one quarter found in North America. As we have briefly touched upon in this series of blogs, oak trees provide opportunities for healthy habitats for many other species. For information and further discussion on the relationships between caterpillars and oak trees, please see The Nature Of Oaks, by Doug Tallamy.
In the last blog, we discussed oak trees as a keystone species, substantially affecting the types and abundance of other species in their habitat. There are 400-500 species of oaks worldwide, supporting an extraordinary 2,300 wildlife species not including fungi, bacteria, and other microorganisms. Oak trees in all stages of life and death have numerous biotic relationships with wildlife.
Badger in tree cavity by Byrdyak, Getty Images||Golden millipede in Lagos by efeghali, Getty Images||Neanura springtail by Henrik_L, Getty Images||Pileated woodpecker in oak tree by mtruchon, Getty Images||Slug & rollie pollies by Sonya Kate Wilson, Getty Images||Wood Mouse in tree cavity by byjohn, Getty Images
Fungi are often identified as attacking oak trees, but they can have very beneficial relationships. Fungi growing in the ground assist an oak tree in getting nitrogen, phosphorous, and other nutrients out of the soil, and in return get carbon and energy from the sugars in the tree’s sap. Oaks provide a place to live for over 700 species of lichens, plus uncounted liverworts and mosses. Lichens covering the oak’s surface help to keep them free of fungal infections and invasive insects. Liverworts and mosses help oaks to retain water and release it into the soil over a long period of time. As oak limbs fall and decay, water retention softens the wood providing food and habitat for decomposers.
Green moss on oak tree by tntemerson, Getty Images
Fungi on oak tree stump by Rixie
Lichen & peat moss on oak by Sean Gardner, Getty Images
Fallen oak leaves are slow to decompose due to their tannin and lignin content, both preservative compounds. Leaf litter, composed of several layers of fallen leaves, becomes habitat for many millions of species including millipedes, springtails, woodlice, slugs, beetles, ants, and other organisms that feed on decaying plants. Through their activities, the creatures of the leaf litter help to return nutrients to the trees.
Oak forest leaf litter by Tina_C_Olsen, Getty Images
Acorns, with high amounts of fats, proteins, and carbohydrates, are one of the healthiest and most sought after foods in the woodland. White oaks, living between 200 and 300 years, will produce about 3 million acorns during their lifetime. Many bird species eat acorns, but oak trees enjoy a special relationship with blue jays, whose beaks are strong enough to pry an acorn open. In autumn, blue jays enjoy feeding on acorns, but also cache them for winter, burying several at a time under a few inches of soil in various locations up to a mile from the originating tree. Although blue jays cache large quantities of acorns, they can only remember and retrieve about 25% of them, allowing many new oak trees to grow and spread into new areas.
Blue jay with red oak acorn by mirceaux, Getty Images
Oak trees support 31 mammal species who consume acorns for food, use the tree for shelter, or use the surrounding habitat for hunting. Gray squirrels and red squirrels favor acorns in the autumn and throughout the winter from caches hidden in nearby locations. They remember far more cache locations than blue jays, but there are still uneaten acorns that will germinate in spring to start new trees. Acorns are also a favorite food for badger, deer, wild board, and wood mouse.
Gray squirrel eating acorn by viktor2013, Getty Images
Red squirrel with acorn by Neil_Burton, Getty Images
Oak trees offer shelter for many species. Squirrels often build their nests high up among the leaves that provide protection from weather and predators. Dead branches, especially those with cavities, may remain on the tree for many years, providing excellent roost sites for bats. Open limbs, leafed areas, and cavities all provide nest sites for a variety of birds. In addition, the many insects drawn to oak trees provide a ready source of food for all of these nesters. Humans have been acorn consumers for millennia. Raw acorns, high in tannin content, can be toxic in larger quantities; but, properly prepared, acorns are high in calories, vitamin C, starch, magnesium, calcium, phosphorous, and antioxidants. They have been a food staple in many cultures and can be found in the records of ancient Greeks, Iberians, Japanese, and English.
Oak trees have many direct and indirect relationships with insects, which we will explore in the next blog.
Seventy percent of the Earth’s surface is under the ocean, and only a small portion is in shallow water along continental shelf areas. The ocean is divided into five zones; the sunlight zone, above 650 feet; the twilight zone, extending to 3300 feet; the midnight zone, down to 13,000 feet; the abyssal zone, down to 21,300 feet; and the hadal zone, extending to the bottom of the ocean. Below 3,000 feet, no light penetrates from the surface; the water temperatures are freezing; and oxygen levels are very low. The pressure exerted on any surface at sea level is 14.7 pounds per square inch (psi), and humans can withstand three to four times this amount, or 45 psi to 60 psi. At 3,000 feet deep, the pressure is 1,345 psi.
Ocean zone chart by DonArnold, 2023
Delta submersible by Robert Schwemmer, CINMS, NOAA, Oct 2010
Pressure keeps sea water from becoming solid ice, even when it is at freezing temperatures. It also makes exploring the ocean difficult, requiring special submersible vehicles. Everything moves more slowly under pressure, and a submersible can take an explorer deep into the ocean given enough time and oxygen. Deep sea creatures can survive because the structure of their bodies is lean and contain no air spaces. Let’s take a look at a few of the wondrous creatures that live in these habitats.
Humpback anglerfish by August Brauer in Public Domain
In the darkness of deep areas, many species find food and mates by touch. Others may use bioluminescent communication – the ability to create light from a chemical reaction between luciferin and oxygen within an organism’s body. Lights show up as spots of various colors on different parts of the body and may be used for attracting a mate, confusing a predator, or attracting prey. Lanternfish have several spots located on their heads, undersides, and tails. Female anglerfish and dragonfish have a shaft that protrudes from their head out in front of their mouths with a glowing tip attracting prey within striking distance. Gulper eel use the lighted tip of their tail as a lure to attract a meal.
Tripod fish by NOAA Okeanos Explorer Program, Public domain, 2010
Fangtooth fish by Sandra Raredon-Smithsonian Institution, Public domain
Tripod fish have two pelvic fins and a tail fin that are elongated and can be filled with fluid to stiffen them, allowing the fish to stand on the ocean bottom while conserving energy. Two long, wavy pectoral fins act as arms to detect prey floating or swimming by and push the prey toward their mouths. Fangtooth fish is another species that can detect vibration and nearby movement. This species is only six inches in length, but have the largest teeth in proportion to their body size of any fish in the ocean. The long lower fangs fit into pouches in the roof of their mouths so their teeth do not pierce their brain cavity.
Dragonfish teeth array by UC San Diego Jacobs School of Engineering, May 2019
The dragonfish, another small fish about six inches long, has a frightening array of teeth located on its jaws and tongue. Their teeth are transparent and their bodies are black, making them impossible to see even in depths where there may be some light. The jaws are loosely hinged, allowing the fish to open its mouth wider than normally hinged jaws would allow. Prey swimming nearby may not notice the wide opening, nor be able to detect the transparent teeth, making the dragonfish a top predator of invertebrates, squid, and shrimp. In addition, when biting, they inject a highly toxic poison to paralyze and kill their prey. This toxin can be dangerous to humans getting bitten or attempting to eat this species.
Giant spider crab by Michael Coghlan, Jan 2014; Gulper eel by Claf Hong, Mar 2005; Lanternfish, Myctophum punctatum1 by Emma Kissling
Some fish practice diel vertical migration, a pattern of movement where a species feeds near the surface at night and moves back into deeper waters to rest during the day. Lanternfish come up to feed on zooplankton and fangtooth fish feed on squid in shallow waters. Some species, including anglerfish and gulper eels, have elastic-like skin for their mouths and stomachs. Mouths can be opened extremely wide to swallow prey larger then themselves. The food is contained in a similarly elastic stomach which shrinks slowly as digestion progresses. Several different species of spider crabs roam the ocean depths scavenging for meat or plant material that falls to the bottom.
Deep-sea animals are seldom seen, but are not immune from climate change and human impacts. Scientists continue to study changes in deep-sea food webs caused by overfishing, ocean acidification, and expanding low-oxygen zones. Learn more about the habitat and species of these areas at the Jurica-Suchy Nature Museum at Benedictine University or your local nature museum or aquarium.
A lot of creepy critters are starting to show up in my neighborhood as Halloween approaches. Many people are putting out scary pumpkins, bats, spiderwebs, and spiders. There are about 3,000 species of real spiders in North America, and all spiders have fangs that inject venom used to paralyze or kill their prey.
Spider web house by Stephanie Wallace, Oct 2007
Spiders are normally quite timid and must be threatened or provoked before they will attack a species larger than themselves. All spiders will bite, but most species do not have teeth that are large enough to break human skin. Of those that can bite through our skin, only four species dangerous to humans are found in North America. They belong to two groups, the widow spiders with three species in North America and the recluse spiders with eleven species in North America.
Widow spiders are all commonly called black widows, but they are actually three different species located across North America and include the western species, Lactrodectus hesperus, the northern species, Lactrodectus variolus, and the southern species, Lactrodectus mactans. In northern Illinois, the northern widow is a small species between 1/8″ and 3/8″ long. Males have long abdomens with white and red markings while females have more rounded abdomens with a red hourglass marking on their underside.
Northern black widow, Lactrodectus variolus, male by Judy Gallagher, May 2018
Northern black widow, Lactrodectus variolus, female by Andrew Hoffman, May 2012
Widow spiders are shy and tend to remain hidden under logs and stones, or just inside entrances to animal burrows. During autumn, as temperatures drop, they will move inside if possible and are often encountered under furniture, boxes, or discarded items that are not often disturbed. Webs are funnel-shaped and provide for adults and eggs. Once eggs are laid, the female will rarely leave the eggs untended, and will aggressively protect them from all harm, attempting to bite anyone that disturbs her or the eggs.
Black widows tend to flee rather than bite, unless they are protecting eggs. Only the females bite and their venom is especially dangerous to humans, but bites are not painful and may not even be noticeable at first. Severe stomach cramping develops within an hour or two and breathing may become difficult. Despite the uncomfortable effects, black widow bites are lethal in less than 1% of cases.
The brown recluse, Loxosceles reclusa, is the most widespread of the recluse spiders, and is often found in or around human dwellings. Other recluse species are found in very limited areas. Their favorite outdoor spots are under boards, stones and log piles, but they are most often found inside in quiet areas on the floor or behind furniture. Adult spiders are a light yellow-brown with a dark violin-shaped marking on their back. Adults are between 1/4″ and 1/2″ long with long, thin legs that can be three to four times the length of their body.
Brown recluse, Loxosceles reclusa, by Mike Keeling, Jan 2008
Recluse spiders are not aggressive and will only bite when disturbed. Most bites occur when the spider is caught in an article of clothing that is picked up off the floor, startling the spider. Once bitten, the wound develops a crust with a red zone around it. The crust may fall off rather quickly but leaves a crater behind that may take several months to fully heal. Although their bite may cause tissue damage, there have been no confirmed deaths in the United States.
Halloween is a special time of year and can be a fun time with scary creatures and other haunts. The Juricha-Suchy Nature Museum is hosting its 13th annual Creepy Critters Halloween Open House on October 26th (for info, please call (630) 829-6546 or email JuricaSuchyMuseum@ben.edu). I hope you get out for some trick-or-treating of your own, and let the real spiders live quietly in their own habitats.
This week we take a look at one other group of species found in the forest litter, those that we can best observe using a hand lens. Springtails are tiny insects colored gray, brown, and white. They are wingless with a worm-like body, and are named for a unique abdominal structure that allows them to suddenly jump. They are extremely numerous, ranging from 500 to 50,000 individuals per square meter. Springtails may form dense groups that come out in winter on top of new fallen snow earning them the nickname “snow fleas.” They are an important species of decomposer feeding on fungi, decaying vegetation, and live vegetation.
Springtail, genus Isotoma, by Ryszard, Aug 2009
Springtails, aka Snow Fleas, by mwms1916, Mar 2015
Soil mites are members of the arachnid family, the same as spiders. When viewed up close, they may look like tiny spiders having four pairs of legs, and a rounded, glossy abdomen in a variety of dark earth tones. Soil mites are decomposers, as well as predators. They feed mostly on decaying vegetation, but also eat springtails, round worms, and fungi.
Red velvet soil mite, Trombidium sp, by Alexey Nikodimov, Apr 2018
Pseudoscorpions, also called false scorpions, look like real scorpions without the dagger-like abdomen. They carry no poison, but have two large claw-like appendages in front. They are predators of springtails, soil mites, and certain worm species. Pseudoscorpions have no eyes or ears, living in the dark soil just below the leaf litter. Almost as numerous as springtails and soil mites, they depend on scent and vibration to locate their prey.
Pseudoscorpion by Philippe Garcelon, Mar 2021
Pseudoscorpion by Philippe Garcelon, Oct 2018
Other animal species that can be observed with either your eyes or a hand lends include ants and beetles. These two groups are quite diverse and can be found in all habitats and soil types.
Bark beetle, by Katja Schultz, Jul 2017
Eastern Bess beetle larva, by Katja Schultz, Jul 2014
Ground beetles by Bernard DuPont, Feb 2006
Beetles make up the largest order of insects with over 300,000 known species. They can be found under decaying logs, under loose bark, and in the leaf litter. They are especially attracted to light sources at night. The larval stage of a beetle is called a grub, often found in shallow soil layers both on the forest floor as well as in our own backyards. Beetles feed on decaying vegetation, live roots, and other plant parts. They are a major food source for a variety of birds, mammals, arachnids, and other predatory insects.
Ants in bark by Michael Jefferies, Mar 2010
Ants are another insect group, forming vast colonies organized into social castes. There is a single queen in each colony plus thousands of workers and soldiers. Each individual has an appointed job serving the colony. Ants provide several ecological functions in any habitat: predators, scavengers, pollinators, recyclers, and soil aerators. Ant species are split into four groups identified as carpenter ants, little black ants, red ants and fire ants.
Hidden Hollow by DonArnold, Nov 2016
Forests are stopping grounds for many migrating species of birds, mammals, and insects. Forest litter is an excellent layer of insulation, and many of the species we have reviewed are active throughout the year, providing food for migrators and ecological services to the other year-round inhabitants. I encourage you to get out and observe this exciting habitat as you hike the forest paths this autumn.
Last week, we started to look at the forest floor and the litter covering it, composed of leaves, dead wood, animal carcasses and other organic waste. A complex community of organisms thrives in this habitat, working to return the nutrients from the litter back to the soil to be used again as food for green plants. The first layer of this community consists of decomposers. This week, we investigate several other layers.
Forest floor & rotten log by DonArnold, Sep2022
Old wood by DonArnold, Sep2022
Many species can be spotted among the litter, but observing them takes patience. Carefully sorting through leaf litter is a skill learned through practice. Overturning decomposing logs and probing through rotting bark will yield great results if done slowly and without great disturbance to the animals present. Animals can be observed with your eyes, a hand lens, or a microscope.
Using your eyes, there are several species that like moist conditions and are easily found under decaying logs. Many are very active after an autumn rain. Some of the more abundant species are:
Slugs are a type of mollusk with a soft, slimy body that leave a slime trail wherever they go on their nighttime feeding excursions. They eat decomposing leaf litter and animal remains.
Slug, Maple Grove by DonArnold, Sep2022
Snail, Maple Grove by DonArnold, Sep2022
Snails, another mollusk, are covered with a hard shell for protection from predators and to help retain moisture. They also eat decomposing vegetation and animal remains.
Isopods, also known as wood lice or pillbugs, must have moist conditions because they breathe using gills. Often found under logs after a rainfall, they move quickly using their 14 pairs of legs. There are several hundred species found in field and forest habitats.
Pillbug, Armadillidium vulgare, by Dann Thombs, Dec 2010
Millipedes are segmented and covered by an exoskeleton. Feeding on litter and animal remains, they can be found in any slightly wet area. Millipedes protect themselves when threatened by rolling up into a tight ball.
Millipede, Maple Grove by DonArnold, Sep2022 (3)
Millipede defense, Maple Grove by DonArnold, Sep2022
Several species can be found in any litter conditions. Many are predators, hunting and feeding on other animals. Some often found in our forests include:
Centipedes may look like millipedes, but are predators, eating many smaller insects. The first pair of legs by their head are modified into sharp, poisonous claws used to capture and stun their prey.
Centipede by Gary Lopez, 2007
Spiders have four pairs of legs, no antenna, simple eyes, and powerful jaws with poison glands. The injected toxin liquifies the soft tissues inside the victim’s body, allowing the spider to suck them out. Many species, including the popular wolf spider, are ground dwelling, digging burrows and hunting by night.
Wolf spider by RWarrin, Feb 2014
Paperbark spider, Maratus pavonis by Jean&Fred Hort, Sep 2015
Harvestmen, also known as daddy long legs, are similar to spiders. They have four pairs of very long legs. When disturbed, they will wave the front two pair around to ward off another predator. They feed on small insects and decaying plants and tend to hunt in groups, mostly at night.
Harvestmen by Chuck, Aug 2007
Harvestmen, Phalangium opilio, by Dann Thombs, Sep 2007
Next we will investigate what a hand lens can reveal about some of the most numerous inhabitants.
Moon jellies are a group of ten species in the genus Aurelia. They are considered true jellies, but DNA testing is required to distinguish between the species. They are found in oceans worldwide in shallower waters common in coastal and upwelling areas where prey is more abundant.
Moon jellies have a shallow, transparent, dome-shaped body and short tentacles that hang down from underneath. Full size adults grow from 12″ to 16″ in diameter. As with all jellyfish, their body is 95% water, and many of the organs found in other animals are missing. Jellyfish lack respiratory, circulatory and excretory systems. They have no lungs, heart, blood, brain, bones, nor teeth. They do have rhopalia, small sensory organs found around the rim of the dome, containing statocyst structures that sense gravity to determine balance and depth in the water.
Moon jellies by Eric Kilby at New England Aquarium, 2009
Dietary requirements of moon jellies are not well understood. Jellyfish are dependent on what the wind and currents bring by to eat. Stinging cells call cnidocytes cover their tentacles and contain nematocysts that can deliver toxin to immobilize prey. Moon jellies are predators hunting fish, mollusks, crustaceans, and other small invertebrates. Food is collected in small pockets along the rim of the dome. There are four arms that transfer the food to the gastrovascular cavity located in the middle of the underside. Digestive enzymes break down the food and nutrients are distributed throughout the body by a system of canals.
Moon jelly, Aurelia aurita by James St. John at Lake Superior Aquarium, 2015
Reproduction includes both sexual and asexual processes. Adult males release strands of sperm into the water which adult females will ingest and use to fertilize their eggs. She incubates the eggs in pockets located on her four arms. Eggs hatch and larvae, called planulae, are released into the water. Planulae continue to grow and eventually attach themselves to rocks on the ocean floor. Anchored to the rock, they enter their next life cycle stage known as a polyp. At this time, they can catch, eat and digest their own prey, and may spend several years as a polyp. As a polyp, they begin strobilation, an asexual reproduction process whereby a polyp clones itself and buds off the clone to form an ephyra. Both the polyp and ephyra grow into adult jellyfish. Through an unknown process, polyps can determine when conditions are ideal to enter their final adult form, called a medusa, through sexual reproduction. Strobilation allows the population to expand quickly, while egg production guarantees a diversity of genes in the next generation.
Moon jelly, Aurelia aurita by Keppet at Monterey Bay Aquarium, 2013
Moon jellies are social animals, travelling in smacks, large groups numbering in the thousands that float across great distances. An adult in the wild will live about a year, but may live several years in captivity. During summer, jellyfish try to reproduce daily. At the end of summer, with less food available and energy levels waning, many individuals become susceptible to bacterial diseases and die before winter. In addition, they are food for open ocean predators including ocean sunfish and sea birds. Leatherback sea turtles feed exclusively on moon jellies, and can eat several hundred at each meal.
Moon jelly, Aurelia aurita by Roger Myers at Monterey Bay Aquarium, 2003
In areas of increased human activity, moon jellies tend to thrive due to a decrease in competitors for food. Moon jellies do well in waters with low dissolved oxygen concentrations and high nutrient loads. When food is limited, moon jellies can shrink to one-tenth of their full size, returning to their previous size as food opportunities become more abundant. A recent study identified the moon jelly as one of the “immortal jellyfish” groups. Several individuals have been observed reversing the aging process, becoming younger all the way back to sexual immaturity, and then aging back to adults. Studies hypothesize that this is an unending cycle. You can view these incredible creatures at many of the world’s aquariums including the Shedd Aquarium in Chicago.
Argiope aurantia, a large spider with black and yellow markings, is a common visitor to many gardens. I watched one in our garden weave a new web. The spider started by attaching a strand of silk to an anchor point about halfway up a sunflower stalk. Then the spider dropped downward, releasing a strand of silk behind it until reaching a new level. It attached the strand to a single point and doubled the strand back to the beginning point. It repeated this process to several new points around the first anchor, eventually creating a pattern that looks like the spokes of a wheel. Each strand is stretchy, and as soon as it leaves a strand, its weight having stretched it downwards, the strand snaps back to a taut line between its two end points. The spider then starts to make a spiral from the center point working outward.
Orb-weaver laying tripline by Pepperberryfarm, 2018
Spiders are classified by the type and shape of the web they weave. Funnel weavers make a cone of dense silk walls that taper downward directing the prey to the bottom where the spider waits. Others spin a variety of silk strands with no discernible pattern. Orb-weavers, like the one described above, construct a large circle with spokes radiating out from the center. Hunting spiders do not weave webs at all, preferring to stalk and chase their prey.
Orb-weavers hard work, by Julie Falk, 2016
All spiders produce silk for use in reproduction, web-building, comfort, and moving around their habitat. Spiders can produce two kinds of silk strands, ones that are dry and ones that are tacky. After laying their eggs, females will use tacky silk to wrapped each egg into a silk sac for protection and warmth. Burrowing spiders use strands to line the inside walls of underground dens. Dry strands become draglines used to climb on or hang from when moving from one perch to another.
Black & Yellow Garden Spider, Argiope aurantia, with prey by Judy Gallagher, 2019
The spokes of an orb-weavers web are made from dry silk strands. The spiral wound from the center across all the spokes in several circles, each larger than the previous one, are made from tacky strands. Insects encountering the web by crawling or flying into it get caught by the tacky strands and are trapped. A single dry strand called a trip line runs from the center of the web to the spider sitting quietly underneath the web. When the struggling insect vibrates the web, the trip line signals to the spider to come out, biting the insect to inject venom, and wrapping its prey in more silk. The prey is left hanging in the web for a later meal.
Leucauge decorata, Silver orb spider, on dragline by Frank Starmer, 2007
Orb weavers and their webs are easy to find. They eat many insects in our gardens and are a natural form of pest control. They make great subjects to observe to learn many of their behaviors including building webs, catching prey and feeding. In summertime, you may also observe courtship, mating, and egg-laying activities. Watch for these easy to find and fascinating garden companions!
Is it a hundred-legger or a thousand-legger? It’s “one of those things with all those legs!”. “Those things” are members of the sub-phylum Myriapoda, “many-legged,” containing over 16,000 species of centipedes, millipedes and others. They were some of the first animals to leave water and adapt to living on land about 250 million years ago.
Centipede by Gary Lopez, 2007
Millipede by Andrew, 2011
They share a common habitat and many similar characteristics, but centipedes and millipedes have several distinguishing attributes by which we can tell them apart. In North America, both animals are between 1/2″ to 6″ in length. Millipedes are black with light markings and have a round, tube-like body. Centipedes are pale yellow to dark brown with a flat body. Both have exoskeletons, a hard outer shell providing protection for the soft parts of their inner bodies. As the animals grow, they shed their exoskeletons and grow a new one. Millipede shells are made from calcium, a hard and inflexible material. Centipede shells are made from chitin, a fibrous substance that is hard to penetrate, but is flexible to allow the animal to bend or flatten.
House centipede by PRkos, 2006
All species of centipedes and millipedes have many pairs of jointed legs. Centipedes have one pair of long, slender legs for each body segment, allowing for high-speed movement when chasing prey or escaping danger. Millipedes have two pairs of short, stubby legs per body segment that are used mainly for pushing when digging burrows. While still in the egg, millipedes undergo a fusion of every two body segments, resulting in each segment having four legs. While milli means one-thousand and centi means one-hundred, the greatest number of legs is 750 and 254 respectively.
Common centipede by Roadsidepictures, 2009
Centipedes and millipedes do not compete for food but do share the same habitat, under leaf litter, in burrows of loose soil, and cool, damp places. Millipedes are decomposers, able to chew and tear plants efficiently. They cannot break down cellulose easily by themselves, but prefer to eat plants already partially consumed by bacteria and fungi. Centipedes are carnivores and their first segmented pair of feet end in a set of lobster-like claws used for catching and rending prey including silverfish and cockroaches. The claws are sharp and contain venom ducts for stunning prey.
Millipede in defensive posture by Matthew Venn, 2007
Myriapoda generally live in dark, humid places because they cannot protect their bodies against water loss. Many centipedes have light gathering sensors located over the entire body to help them detect brighter areas and stay well hidden, away from predators with better eyesight. Millipedes may roll up and play dead when threatened, exposing only their hard exoskeleton to predators. Other millipede species exude a sticky glue-like substance behind them to slow down predators, and still others have the ability to spray an attacker with hydrogen cyanide from ducts located along each body segment.
Narceus americanus, millipede by siralbertus, 2013
Centipedes and millipedes both provide vital environmental services. Centipedes eat a variety of smaller insect prey including earthworms and household spiders. Millipedes are detritivores, feeding on decomposing vegetation and organic matter. Sow bugs, pill bugs and millipedes together reduce the amount of leaf litter built up on the forest floor by about five percent each year. Whenever you have a chance, I urge you to take a closer look at these wondrous garden denizens.
Spiders are omens of good luck, and the bigger they are, the more luck for you. If you see a spider on Halloween, it means that a deceased loved one is watching over you. According to folklore, spiders have mystical powers with their ability to spin both physical and magical webs. The name spider is from “spinder” a reference to its spinning ability. The Greek goddess Arachnea was jealous of her rival, the goddess Athena and challenged her to a silk spinning contest. When Arachnea lost, Athena turned her into a spider destined to spin silk forever. There are more than 600 species of spiders in Illinois with about 60 of those common to northern Illinois. Let’s take a closer look at spiders and their abilities.
Spiders are part of the largest phylum of animals on earth: arthropods, which include crustaceans, insects, myriapods (millipedes and centipedes) and arachnids (spiders, scorpions, mites and ticks). Spiders are characterized by having eight legs and two body parts, the cephalothorax and the abdomen, connected by a narrow portion called the pedicel.
Spider & Web by Brian Rogers, c-2014
We may characterize the cephalothorax as the head, with the spider’s face in front, mouth at the bottom, and all eight legs attached to its underside. Internally, the cephalothorax contains the venom gland, the brain and the sucking stomach. At the top of the face are six to eight simple eyes arranged in two rows from left to right. Each eye is a single lens, but all can detect color, movement, shape and size. Below the eyes are two vertical jaws lined with teeth and tipped with fangs. The fangs are used to inject both poison to disable and kill a victim and enzymes to break down a victim’s internal tissue to a liquid form. Located below the jaws is another pair of appendages called pedipalps. These are used when holding prey and feeding and are used in mating on fully grown adult males.
The abdomen contains all remaining organs including heart, intestines, book lungs and trachea, ovaries and silk glands. The abdomen may be long and thin or large and bulbous and is often colorfully marked. These distinctive colorings are useful for species identification. At the very back of the abdomen are three pairs of spinnerets. Each one attaches to an internal silk producing gland. Silk is a liquid mixture of proteins, which when exposed to air, dries immediately to a threadlike, elastic material. It can be stretched up to three times its original length, and the tensile strength is greater than that of solid bone. Each gland may produce a different type of silk. The spider uses silk, both sticky and non-sticky strands, to form webs. A web may be designed as a sheet, a funnel, a circular orb or in an irregular jumble of strands. Other uses for silk are for wrapping prey for later consumption, creating the outer covering of an egg sac, or to create a shelter. Silk is used in two ways for movement. One is to create a dragline, which a spider attaches to an anchor point, such as a tree limb or house eave, and uses it to lower themselves. The second movement, used by immature spiders to leave home, is called a balloon string. The young spider points its abdomen skywards and shoots out a set of three threads in a triangle pattern designed to catch the wind and fly them to new territory. Ballooning usually takes the spider several inches or feet to the next branch, but it has been known to transport a spider over many miles. The last use is to create a sperm web, which I will discuss below. Silk is reusable, and all spiders consume their webs after each use, returning the proteins to liquid form available to be re-used within minutes.
All spiders are predators and hunt for food. Favorite foods include other arthropods as well as other spiders. Adult females are considerably larger in size than adult males who must impregnate the female without getting eaten. When males reach sexual maturity, the ends of their pedipalps enlarge to form a sperm holding chamber. A sperm web is formed from silk and sperm is laid on this web to be taken up into the pedipalps where it is stored until needed. To avoid being eaten, males will court a female to clearly establish his intentions. For species with poor eyesight, the male will walk onto a female’s web using an intricate pattern of vibrations that indicates he is not prey. For species with good eyesight, the male will get in front of the female and perform a courtship dance or combination of poses.
Crab Spider in Yellow by Judy Gallagher, c-2016
Once the female accepts the male, his sperm must be deposited from each pedipalp into the epigynum, an opening on the bottom of her abdomen leading to the ovaries. He will climb on the back of her abdomen, reach around and deposit sperm from both pedipalps and leave. Males may mate with more than one partner, but most will die shortly after mating. Eggs are produced and fertilized during the summer, then deposited in an egg sac. The egg sac may be carried around by the female or attached to the edge of her web. Egg sacs may contain from one to several hundred eggs. Eggs will hatch within a few weeks, depending on the species. Spiders are born blind but will grow functioning eyes within several days of hatching. The young stay close to the egg sac to use it for nourishment until they can see and begin to hunt for themselves. The young will molt from four to twelve times, growing functional eye tissue, fangs and spinnerets during subsequent molts. Any lost body parts, such as a leg, can also be regrown during a molt, however once they are adults, they will never molt again. The molting process normally takes several months and many species will spend their first winter between molts, having their final molt during spring of the following year.
Following the first or second molt, juveniles are able to feed themselves and will begin to hunt on their own. As predators, they quickly find that other spiders make good meals, and cannibalism in large hatches is a reality. In general, spiders are either active hunters, typically found in species with good eyesight, or web weavers, typically those species with poorer eyesight. For web weavers, all prey is caught in a web. Prey thrashes about getting more entangled until the prey tires. Spiders can tell from the vibrations at which point they can safely move in and using their fangs, inject venom to further subdue and kill the victim. At the same time, enzymes are also injected to break down internal tissues into liquid form. Active hunters will lie in wait or chase down prey. Many active hunters use coloration to blend in with flowers and other vegetation while hunting. Some species, including crab spiders in our area, can change their body colors to match different flower colors. Spiders eat all meals in a liquid state and have powerful stomach muscles that pull all liquids into their stomach.
Crab Spider in White by Michael Figiel, c-2016
All spiders produce venom. In northern Illinois, there are only two species that may pose a serious threat to humans. They are the Brown Recluse, Loxosceles reclusa and the Northern Widow, Latrodectus variolus. Both of these species are native to areas farther south and are not commonly found in northern Illinois. It is thought that they only occur when brought into an individual home from elsewhere. Spiders, in general, including these two species, are not known to bite unless provoked. Most spiders live an average of one to two years, although some species in the tropics may live up to 20 years. Their most effective predators are found among wasps. Two wasp families will repeatedly sting the spider until it is paralyzed, then drag it off to their nests. Instead of eating the spider, the wasps lay an egg on the spider’s abdomen, and when the egg hatches, the larva will feed on the still living spider until it dies and the wasp pupates. Other predators include fish, frogs, toads, salamanders and other spiders. Spiders are one of our gardens most beneficial inhabitants, eating many of the garden’s numerous flower and vegetable pests.
Winter is the time of least activity, but warmer days or when the sun is providing radiant warmth, you can observe spiders being active even on top of the snow. Most overwinter in leaf litter, under bark or in hollow logs or crevices. If they decide to move inside with you and you prefer they didn’t, they can easily be captured with a paper cup and a lid (3×5 cards work well) and released outdoors. However, they will do a good job patrolling insect pests, including aphids on indoor plants, as well. There are many good books and websites to get more information. A couple of my favorites include “Good Garden Bugs” by Mary M. Gardiner, Ph.D.; “Spiders of the North Woods” by Larry Weber, part of the North Woods Naturalist Series; and a video of ballooning on the Science Magazine website found at watch-ballooning-spider-take-flight.
