Predators with Personality

Brownish-Grey Fishing Spider (Dolomedes tenebrosus) Photo by Frank Kaczmarek.

A living jewel hangs suspended beneath the microscope. An emerald sheen shifts with its every pulsing breath over iridescent silver, gold, and bronze swirls. Aquamarine legs hang poised, deftly manipulating invisible threads. The creature under magnification is an orchard orb weaver: a member of the spider family Araneidae and an animal not normally celebrated for its beauty, or indeed, celebrated at all.

For many, the appearance of a spider occasions a scream of “Spider!” (and maybe a reach for a shoe) with little further examination. They are symbols of evil or bad luck, assumed to be dangerous. In truth, spiders are shy and retiring creatures. As skilled predators, they are significant consumers of insects. Indeed, spiders can make up half the predator biomass on the forest floor. And while all spiders have a venomous bite, it is used on prey, and only rarely in self-defense.

A closer look at spiders – and since most are smaller than half a centimeter, a closer look is required – reveals an amazing array of forms and behaviors. There are almost 4,000 known species north of Mexico. While there are no official estimates for the number of spider species in the Northeast, a recent student collecting trip in the Burlington, Vermont, area found over 100 species in each of two locations. Spiders come in a range of sizes and shapes, from fat gray orb-weaving barn spiders to fast and tiny iridescent jumping spiders. They pursue a variety of life strategies, from ambushing to active hunting, orb webs to cobwebs to no webs.

What follows is an introduction to seven commonly seen spider families; the idea is to showcase important differences between each and, hopefully, squash the casual perception that a spider is just a spider.

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Image source: Wikipedia

Pholcidae
Cellar Spiders

If your housekeeping is like mine, you’ve seen a cellar spider. The most common ones are skinny gray-brown spiders, with disturbingly long legs, that hang in the corners of houses and other manmade structures. They can be confused with other long-legged arachnids like the harvestmen (daddylong-legs), but most cellar spiders have a distinctive front section and an elongated abdomen, while a harvestman, which is not technically a spider, has just one spherical body part.

Pholcidae is a large family, distributed across the world. Several pholcid species, most notably the long-bodied cellar spider (Pholcus phalangioides) have closely associated themselves with humans and now live worldwide.

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Longbodied Cellar Spider, Pholcuz phalangioides.
Illustration by Rachel Sargent.

Cellar spiders make tangled webs, which look messy to human eyes, but are effective at snaring prey even without the sticky properties of orb webs. These spiders are opportunistic feeders and will eat anything small enough to catch; they’re not above cannibalism and often invade neighboring webs and eat the neighbor. A disturbed spider will hang from its web and vibrate so quickly that it becomes a blur, making it difficult for a predator to catch. Female cellar spiders care for their spiderlings by carrying them around or guarding them on their web.

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Image source: Wikipedia

Araneidae
Orb Weavers

Orb weavers are perhaps the most famous family of spiders, thanks largely to their classic spiral webs. While these spiders typically use the same web strategy, they vary radically in size, shape, and color. Orb weavers are frequently nocturnal, so when you see one hanging in its web, don’t disturb it – it’s getting a good day’s sleep.

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Black and Yellow Argiope, Argiope aurantia.
Illustration by Rachel Sargent.

While you’ll see many different orb weavers in the Northeast, one of the most conspicuous and beautiful is the diurnal black and yellow argiope, Argiope aurantia. They are commonly seen in fields, hanging in spiral webs a foot across that incorporate a bold zig-zag of white silk, called a stabilimentum. The argiope female is up to one inch long, patterned in classy black and yellow. The plainer male is about a quarter-of-an-inch long. They are a gardener’s friend, as they prey on pest insects.

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Image source: Wikipedia

Salticidae
Jumping Spiders

Jumping spiders are the teddy bears of the spider world. With their small, compact, fuzzy bodies, gigantic, round primary eyes, and habit of turning to face whoever is looking at them, it is hard to resist their charm.

This family is larger than the orb weaver family, but jumping spiders are less frequently seen because they’re smaller and don’t usually hunt in houses. Unlike the spiders already described, they do not sit on a web and wait for prey; they are active hunters and earn their name through their ability to jump thirty times their body length. They have excellent vision – hence the adorable gigantic eyes.

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Bold Jumping Spider, Phidippus audax.
Illustration by Rachel Sargent.

Since jumping spiders are so visual, they have evolved elaborate courtship dances, eye-catching colors and patterns, and on the opposite end of the spectrum, ingenious cryptic forms. The bold jumping spider, Phidippus audax, is one of the more noticeable jumping spiders in the Northeast because it is large, has iridescent mouth parts (chelicerae), and is diurnal.

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Image by Simone Ross.

Thomisidae
Crab Spiders

“I found a dimpled spider, fat and white / on a white heal-all, holding up a moth / Like a piece of rigid satin cloth--”

In his poem “Design,” Robert Frost must have been describing the goldenrod crab spider, Misumena vatia, a common crab spider in the Northeast that sits on a flower and ambushes pollinating insects. (They can catch bees twice their size.) Goldenrod crab spiders are found on yellow or white flowers because the females can slowly change their color between white and yellow to match their flower choice – they’re the chameleons of the spider world.

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Goldenrod Crab Spider, Misumena vatia.
Illustration by Rachel Sargent.

Crab spiders are almost as numerous as orb weavers and, like the orb weavers, are colorful and easy to spot. They are aptly named for their resemblance to crabs, both in shape and in their habit of scuttling sideways.

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Image by Richard Migneault.

Agelenidae
Funnel Weavers

Bedecked in various shades of brown, funnel weavers are not as glamorous as some spiders. (They’re boring enough that even experts have a hard time telling different members of the family apart.) But you’ve undoubtedly seen them. This family likes to build its webs in meadows and bushes, or sometimes between window screens. On dewy mornings in late summer, look for funnel spider webs scattered in silvery patches across your lawn. These were made by grass spiders, Agelenopsis spp.

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Grass Spiders, Agelenopsis spp.
Illustration by Rachel Sargent.

Funnel weavers build a sheet web with a tube-like funnel at one end that acts as a refuge and a sensor – the spider responds to vibrations on the web by either dashing out of its funnel to grab the prey or retreating into its hiding place.

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Image by James Reben.

Pisauridae
Nursery Web Spiders

I went to my stove to make tea one morning and found that a large brown spider had taken over a gas burner overnight and hatched her egg sac before expiring. The entire burner had become a nursery web with hundreds of pin-head-sized spiderlings suspended by invisible threads. Every breath of air caused the cloud of spider siblings to shift in an eerie choreography.

The spinning of a nursery web is a classic characteristic of this family. They are dedicated mothers, carrying their egg sac in their jaws before spinning a nursery web for the hatchlings and, if the mother lives long enough, guarding the helpless spiderlings. The most commonly seen species in this group bears the same name as the family, the nursery web spider, Pisaurina mira.

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Nursery Web Spider, Pisaurina mira.
Illustration by Rachel Sargent.

Nursery web spiders are common across North America and often move into houses. Some species are seen along shorelines, because they can run on the surface tension of water. They are active, hunting down their food instead of waiting on a web. These stocky, brown spiders can be confused with the wolf spiders, which also carry their egg sacs.

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Image by Patrick Edwin Moran / Wikimedia.

Lycosidae
Wolf Spiders

Wolf spiders are among the most common spiders across the world and, as you might guess from the name, are accomplished hunters. They’re frequently seen, because they come into houses to overwinter.

A female wolf spider will carry her egg sac on her spinnerets, dragging it along behind her and taking it into sun or shade to optimize the temperature for the developing offspring. She assists the spiderlings when they emerge and will carry them on her back.

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Thin-legged Wolf Spider, Pardosa milvina.
Illustration by Rachel Sargent.

The thin-legged wolf spider, Pardosa milvina, is a common sight in the Northeast. They are small for a wolf spider, with spiny legs that help them grip surfaces. Most wolf spiders have stripes that run lengthwise on their bodies, but the stripes of thin-legged wolf spiders are irregular.

 
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