Tag: crab spider

Bug o’the Week – Running Crab Spiders

Bug o’the Week
by Kate Redmond

Running Crab Spiders

Greetings, BugFans,

Long-time BugFans know that the BugLady is infatuated with the lovely, sedentary Flower Crab spiders (family Thomisidae) that she photographs throughout the summer https://bugguide.net/node/view/5610/bgpage, https://bugguide.net/node/view/2383290/bgimage, https://bugguide.net/node/view/1299520/bgimage,  and she recently posted a BOTW about the chunkier Ground crab spiders https://uwm.edu/field-station/bug-of-the-week/ground-crab-spiders/ (also Thomisidae).

Running crab spiders, in a separate family (Philodromidae) have been mentioned briefly throughout the years – here’s their story.

They are “running” by both name and by inclination – they move along smartly, and Philodromidae comes from the Greek “philodromos,” meaning “lover of the race/course.”  There are 92 species of spiders in this widespread family in North America, and they’re usually found on the stems and leaves of plants.  Philodromuis and Tibellus are common genera.

These are not flashy spiders – most are small (measuring less than ½” long), flat-bodied, and drab.  Many (but not all) are crab-shaped like the Thomisids, but in Philodromids, the second pair of legs is noticeably longer than the first.  Eye arrangement is an important tool in spider ID – here’s what it looks like to stare two genera of Philodromids in the face https://gnvspiders.wordpress.com/7-philodromidae-running-crab-spiders/.

Philodromids don’t spin trap webs, but they do generate silk to make egg sacs and to form drag lines that catch them if they catapult off of a leaf in pursuit of prey or if they have to bail in order to avoid capture themselves.  They are, of course, carnivores that eat any small invertebrate that they can ambush and subdue, including other spiders, and they are small enough to become prey of larger spiders, themselves.

Most sources said that their venom (should they even be able to puncture your skin) might result in some pain and swelling, but is not considered dangerous. 

Males encounter females as they wander the landscape.  She leaves a trail in the form of a pheromone-laden silk dragline; he catches up with her and romance ensues.  She conceals her egg sac and guards it (like the female Philodromus guarding eggs that she had stashed in an empty beech nut shell) until her young hatch toward the end of summer, which markedly enhances the spiderlings chances of survival.  The almost-mature spiderlings overwinter sheltered in leaf litter and under tree bark and mature the next year.  A bitterly cold winter takes a toll on overwintering Philodromids. 

The most common Philodromid genus is PHILODROMUS, flat spiders that look similar to the Thomisid crab spiders.  There are 55 species in North America and about 200 more elsewhere.  They’re found on vegetation, but also on the ground or on walls.  Larry Weber, in Spiders of the North Woods, writes that Philodromus spiders are often found in trees (and sometimes inside the house, high on the wall), and that he has collected immature Philodromus spiders on the snow in early winter.

Philodromus spiders don’t spin a web but they may create a silken shelter.

With their cylindrical abdomens, spiders in the genus TIBELLUS (tib-EL’-us), the Slender crab spiders, are un-crab-like crab spiders.  There are seven species in North America and two (or three) in Wisconsin, and some are striped and others are not.  Based on the presence on the abdomen of both stripes and of two spots toward the end, the BugLady thinks she’s photographed Tibellus oblongus, the Oblong running spider, which has a patchwork range across North America https://bugguide.net/node/view/143110/data and is also widespread in the northern half of the Old World.  

When a male Oblong running spider encounters a female, he taps her rapidly with legs and palps, and if she’s agreeable, she remains motionless.  He spins a “bridal veil” that covers her and fixes her to the substrate.  When the show is over, he leaves (in a rush) and she releases herself from the veil.

Today’s Science Word – the Oblong running spider is referred to as an “epigeal” organism, which means that it’s found on/above the soil surface and does not tunnel, swim, or fly.  Oblong running spiders are often seen stretched out on grass leaves – the first two pairs of legs forward, the third pair hanging on, and the fourth pair extended back. 

Like other spiders, Philodromids have superpowers, and one is their ability to walk on smooth, vertical surfaces without sliding off.  How do they do it?  Scopulae (scopulas).  Alert BugFans will recall that many bees have clumps of hairs – scopa/scopae – on their legs or abdomens that allow them to collect and carry pollen.  Same root word – the Latin “scopa” means “broom,” “twig,” or “brush” but scopula is the diminutive form (mini-brush).  Scopulae are dense tufts of hairs that are found below the claws and at their tips on the feet of walking or wandering (non-web-spinning) spiders.  The ends of those hairs are further fragmented, forming many, microscopic contact points for the spider’s foot.  This creates a natural adhesion that is sometimes enhanced by liquid excreted from adhesive pads (alternately, one source suggested that the scopulae respond to a super-thin layer of water that covers most surfaces).

HEADS-UP!  CICADAS ARE COMING!! – https://www.smithsonianmag.com/smart-news/watch-for-cicadas-billions-from-brood-xiv-will-soon-emerge-after-17-years-underground-180986592/?utm_source=smithsoniandaily&utm_medium=email&utm_campaign=editorial&lctg=91269370

Kate Redmond, The BugLady

Bug of the Week archives:
http://uwm.edu/field-station/category/bug-of-the-week/

Bug o’the Week – Ground Crab Spiders

Bug o’the Week
by Kate Redmond

Ground Crab Spiders

Howdy, BugFans,

Crab spiders need no introduction to these pages – several genera of delicate, flower crab spiders https://bugguide.net/node/view/621778/bgpage, https://bugguide.net/node/view/3928/bgpage, https://bugguide.net/node/view/2201967/bgimage have appeared in previous episodes.

Well, maybe a quick review:

 

They are in the family Thomisidae, which has about 130 species in nine genera in North America (14 genera worldwide).  The coolest genus that the BugLady has seen is the genus Tmarus, which can look like tiny octopi https://bugguide.net/node/view/1238420/bgimage.  

Crab spiders do not spin trap webs; they are ambush hunters that lurk on flowers, leaves, or bark, or in leaf litter, waiting for their prey – insects and other spiders – to appear.  They get their name from their ability to walk sideways and backwards using just their four back legs and, of course, from their two pairs of long, thick front legs (the name “crab spider” is shared with several unrelated, crab-like spiders).  They have eight eyes https://bugguide.net/node/view/306006/bgimage, and in some species, the eyes are on tubercles. Their wide, flat bodies are generally less than a half-inch long, and some species can (slowly) change color from white to yellow and back.   

Although they don’t spin trap webs, they do spin silk for reproductive purposes and as drag lines when they launch themselves at prey on a flower top. 

There are sixty-seven species of GROUND CRAB SPIDERS, genus Xysticus, in North America.  Most come in earth tones, and many have a disruptive pattern on their abdomen that helps to camouflage them.  Contrary to the name “Ground crab spider,” they can be found on leaves, stems, and flowers as well as on the ground, on rocks, and on rotting logs. 

The BugLady has a file of Xysticus-like spiders, but (alas), there are several similar genera like Bassaniana (the Bark crab spiders) and Ozyptila (sometimes called the Leaf litter crab spiders), that, along with the Ground crab spiders are more, well, muscular-looking, and that can be tricky to tell apart without looking at the “naughty-bits.  Xysticus also has three or four pairs of macrosetae (large, hairlike projections) on its front legs and a more domed carapace (the covering of the front portion of the spider – the cephalothorax).

They don’t make trap webs, and they don’t wrap their prey before eating it, either.  They station themselves where there’s a lot of “traffic,” grab small invertebrates that get too close, subdue them by wrapping their long, front legs around them, and then kill them with a venomous bite and consume the innards.  They’re eaten by birds, reptiles, and small mammals that forage on tree trunks or on the ground. 

Not many sources took a deep dive into their natural history, and the accounts were a bit contradictory.  Some lumped them in the generalized Crab spider pattern of eggs/spiderlings staying in the egg sac all winter, emerging in spring, and maturing in summer.  Other sources said that the young overwinter as almost-mature spiderlings and that Xysticus spiders have been seen trekking across snow on warm days in winter.  Boy meets girl in summer and he immobilizes her with silk to ensure her cooperation.  He is small and she is large, and she has no trouble slipping her bonds when he leaves.  She will continue to create egg sacs, sometimes folding a leaf around the sac and webbing it partly shut to conceal it https://bugguide.net/node/view/2372239/bgimage, until she dies in fall’s first freezes.  The total life span is about a year in northern climes.

Like many kinds of spiders, male Ground crab spiders are smaller and more angular than females, with noticeably slimmer abdomens (sexual dimorphism), and they have large pedipalps (the segmented, sensory mouthpart-like appendages) that look like boxing gloves https://bugguide.net/node/view/1959514/bgimage.  Larger females can catch larger prey, and so consume the extra nutrients needed to make eggs.  There are several hypotheses about the size difference.  First, females may be larger because they produce eggs, and larger females tend to produce more and healthier offspring, but large size is not an advantage for the males.  Another idea called “male dwarfism” says that smaller males can get around more easily and have a better chance of finding a female.  Still another hypothesis says that the size difference was a chance development and there’s no particular advantage to being either large or small.

Thanks, as always, to BugFan Mike for his spider advice. 

Kate Redmond, The BugLady

Bug of the Week archives:
http://uwm.edu/field-station/category/bug-of-the-week/

Bug o’the Week – Midsummer Memories by Kate Redmond

Bug o’the Week
by Kate Redmond

Bug o’the Week Midsummer Memories

Howdy, BugFans,

Last year the BugLady had so many midsummer stories to tell that she wrote one episode about dragonflies, and a second about “other” (because as seasoned BugFans know (well) her camera gravitates to dragons and damsels).  She’s got a heap of pictures to share again this year, but she’ll mix and match the groups in a two-part summer feature.

ROSE CHAFER BEETLE – The BugLady saw a single Rose Chafer last year and wrote about it https://uwm.edu/field-station/rose-chafer-beetle/.  This year, she found bunches of them – orgies of them (she’s not sure what the collective noun for Rose Chafers is, but she’s pretty sure it’s “orgy”).  And she was enthralled by the leggy designs they made on the undersides of milkweed leaves.  

American Copper
Bronze Copper

COPPER BUTTERFLY – A highlight of the BugLady’s recent explorations of Kohler-Andrae State Park was finding two species of Copper butterflies – American Copper and Bronze Copper (she rarely finds Coppers).  The Coppers are in the Gossamer-wing butterfly family Lycaenidae, along with the Harvesters, Hairstreaks, Elfins, and Blues.  Their caterpillars feed on plants in the rose and buckwheat families (dock, sorrel, and knotweed).

VIOLET/VARIABLE DANCER – The BugLady was talking to a friend recently about the colors that dragonflies and damselflies come in.  Black, black and yellow, green, blue – even red.  But purple?

FLY ON PITCHER PLANT – This is just the way it’s supposed to work.  Insects with a “sweet tooth” get lured to the lip of the pitcher plant and partake of the (slightly narcotic) nectar there.  Judgment impaired, they mosey around a little, maybe venturing onto the zone of down-pointing teeth below the lip, and then onto the slick, waxy zone below that.  It’s all downhill from there.

GOLDENROD CRAB SPIDER on yarrow (not all Goldenrod crab spiders have red racing stripes).  Incoming insects have trouble seeing her, too.  Out of all the species of crab spiders in the world (about 3,000), only a very few have the ability to change colors, and that ability is limited to the female of the species.  Her color palette includes white, yellow, and pale green.  She sees the background color with her eyes, and because a wardrobe change takes her between three days and three weeks she tends to stay on her chosen flower.  Her base color is white, and switching involves either creating yellow pigment or reabsorbing and then sequestering or excreting it.  

Why?  Good question.  Scientists have tested spiders on matching and non-matching flowers (which they often sit on), and they saw no boost in hunting success when the spiders matched their background (she likes prey that’s bigger than she is, like bumblebees, because she has eggs to make.  She loses weight on a diet of small flies).  When spiders themselves are the prey, they are not picked off more often on non-matching flowers.  Maybe the color change gives her some sort of advantage when she forms her egg case, or maybe it’s a vestigial solution to a long-ago problem.

ORANGE-LEGGED DRONE FLY – This Syrphid/Flower/Hover fly is so serious about its bumble bee disguise that it makes a loud buzz when it’s flying

SEDGE SPRITE TUSSLE – the BugLady was in a bog not long ago when she saw two damselflies tussling on some leaves.  At first, she thought there was some predation going on, but that didn’t make sense because they were both Sedge Sprites.  He had grabbed her and was wrestling with her, and she was having none of it.  He suddenly flipped her around and clasped the back of her head with the tip of his abdomen (SOP for mating dragonflies and damselflies).  Rather than reaching forward and taking his sperm packet, she ultimately gave a couple of good shakes and dislodged him.  One small drama.

PHANTOM CRANE FLY – Flies come in all sizes and shapes, but this magical creature in white spats is the BugLady’s favorite.  It lives in dappled, brushy wetland edges where it flickers through the vegetation like a tiny wraith.

FORKTAIL AND POWDERED DANCER – Eastern Forktails are voracious hunters that go after other damselflies, even those close to their size.  The mature female forktail (in blue) found a teneral (young) Powdered Dancer (in tan) that was probably not a strong flyer yet.

Go outside – look at bugs,

Kate Redmond, The BugLady

Bug of the Week archives:
http://uwm.edu/field-station/category/bug-of-the-week/

Bug o’the Week – Early Summer Scenes

Bug o’the Week

Early Summer Scenes

Howdy, BugFans,

Well, the sun has solsticed, and it’s all downhill from here.  Our pre-Christian, Germanic ancestors, who were more intimately attuned to the rhythms of the sun, correctly celebrated the winter solstice, aka Yule (which may have come from the Norse word houl, which referred to the sun as the wheel that changed the seasons).  They recognized that the winter solstice marked a turning point that would lead to longer, warmer days.

In the BugLady’s neck of the woods, the insect world is dominated these days by mining, sweat, and bumble bees and by lots of flies, including a big hatch of mosquitoes that timed their appearance to coincide with the Riveredge Butterfly and Dragonfly count (causing the BugLady to move along the trail rather smartly).  Here’s what she’s been seeing in the run-up to summer.

STILT BUG ON FERN: This started out as a fern fiddlehead picture – the BugLady did not see the stilt bug when she took the picture, it was one of those happy surprises that photographers get when they put an image up on the monitor.  Most stilt bugs/thread bugs are plant-eaters that supplement their diet of plant juices with the odd, small invertebrate.  Some are more “meat-oriented,” and one species is used to control Tobacco hornworms.

CRAB SPIDER: A friend of the BugLady’s recently asked where all of the beautiful, plump crab spiders are.  They’re here, but they have some growing to do.

KATYDID NYMPH: And another friend, from Southern climes, asked if the BugLady was seeing katydids yet.  Same answer.

TIGER BEETLE: The BugLady loves seeing the flashy, green Six-spotted tiger beetles.  Usually they perch on a bare path, wait until you get too close, fly ahead of you about a foot above the ground, land, and repeat the process when you get too close again.  Until this year, the BugLady had never seen one off the ground, but she’s photographed three in the past month.  Get to know Wisconsin’s tiger beetles at https://wisconsinbutterflies.org/tigerbeetle.

MILLIPEDE ON RUST: Millipedes are decomposers/detritivores, feeding on dung, plant juices, and pieces of dead plant materials like decaying leaves, breaking them down for organisms even smaller than they are.  Some like fungi. 

If you’ve seen the invasive shrubs Glossy and Common buckthorn, you’ve probably seen stems and petioles with a bright orange blob on it.  The blob is a rust – a fungus – called Crown rust (Puccinia coronata).  Buckthorn is one of its hosts, and the alternate hosts are a variety of grasses, including agricultural crops like oats and rye.  If you see grass leaves with thin orange streaks on them, you’re probably seeing a variety of crown rust.  Crown rust has a complicated life cycle (http://www.minnesotaseasons.com/Fungi/Crown_Rust.html ), but the bottom line here is that the rust on buckthorn releases its spores in a soupy, sweet liquid that attracts insects, and the insects carry the spores to rust patches on other buckthorns and fertilize them.  The rust probably doesn’t get much bang for its buck when its spores are eaten by a short-legged pedestrian like a millipede.

BALTIMORE CHECKERSPOT CATERPILLER: The astonishing Baltimore Checkerspot https://bugguide.net/node/view/1771510/bgimage and https://bugguide.net/node/view/1636206/bgimage, and its caterpillar, is one of the BugLady’s favorites.  This caterpillar hatched last summer and munched on its host plant (historically white turtlehead, but in the past 50 years, they’ve adopted Lance-leaved/English plantain, and those are the only two plants a female will oviposit on).  It overwintered as a caterpillar, woke up hungry this spring, and looked around, – no turtlehead in sight yet – so it’s been eating a variety of plants, especially white ash.  Both turtlehead and plantain leaves contain poisonous glycosides (turtlehead has more), allowing the caterpillar and butterfly to get away with their gaudy colors.  And remember – the butterfly (and the oriole) get their names not because they were discovered in that city, but because 17th century English nobleman Lord Baltimore, a familiar figure to the colonists, dressed his servants in orange and black livery. Get to know Wisconsin’s butterflies at https://wisconsinbutterflies.org/butterfly.

MONARCHS: Most of the Monarchs that return to Wisconsin are probably Gen 2 – the second generation north of their wintering ground in Mexico.  There ensues two short-lived generations – Gen 3 and 4 – whose only job is to increase the population, and these two clearly got the memo.  Gen 5, produced in August, is the generation that is signaled by both waning day length and the lowering angle of the sun to migrate instead of reproducing (though there always seem to be a few that didn’t get that memo). 

BEE ON LEATHERWOOD: At a quick glance, you might think that this is a bumble bee, but bumble bees have hairy butts.  The BugLady thought this was a carpenter bee (which have shiny butts), but now she thinks it’s one of the larger mining bees in the genus Andrena.  Leatherwood is a spring-blooming shrub in woodlands – those fuzzy bud scales protect the bud from chilly spring nights.  It gets its name from the fact that its branches can’t be torn off the shrub, and from its strong bark fibers, which were woven into baskets, bowstrings, ropes, and the cords that lashed together canoe frames.  Settlers used its branches when they took their children to the woodshed.  All human use of it is problematic, because its caustic bark raises some serious blisters.

ROBBER FLY: Another bumble bee look-alike.  Bumble bees eat nectar and collect pollen to feed their larvae; robber flies are carnivores.  Laphria thoracia (no common name) can be found on woodland edges from the Mason-Dixon Line north into the Maritime Provinces and west through the Western Great Lakes.  Adult Laphria thoracia eat bees and adult beetles (this one has a clover weevil, but the BugLady recently photographed one with an assassin bug), and their larvae feed on beetle larvae in decaying wood.  Get to know Wisconsin’s robber flies at https://wisconsinbutterflies.org/robberfly  

GOLD-BACKED SNIPE FLY: June is the only month to enjoy these dramatically-colored flies that perch low in the vegetation in moist areas. 

SWAMP MILKWEED BEETLE: The BugLady loves finding these “ladybugs-on-steroids.”  They’re often tucked down into the axils of the milkweed leaves, and when they see company coming, they either duck down deeper into the crevice or they default to the typical escape behavior of an alarmed leaf beetle – they tuck in their legs and fall off the plant.  Their bright (aposematic/warning) colors tell potential predators that they are toxic, due to the milkweed sap they ingest, but damsel bugs, stink bugs, and flower/hover/syrphid fly larvae prey on them nonetheless.  For the full (and fascinating) Swamp milkweed leaf beetle story, see https://uwm.edu/field-station/swamp-milkweed-leaf-beetle/.  

ICHNEUMON WASP: Every year, large and colorful Therion (probably) Ichneumon wasps drift through the vegetation in perpetual motion, legs dangling, taunting the BugLady https://bugguide.net/node/view/739675/bgimage.  They often occur in wetlands, and the BugLady swats mosquitoes and deer flies as she waits for them to show their faces.  Which this one did.

Experienced BugFans are saying, “But, but, but – where are the dragonflies?”  Tune in next week.

Go outside – look for bugs.

Kate Redmond, The BugLady

Bug of the Week archives:
http://uwm.edu/field-station/category/bug-of-the-week/

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