Predator and Prey: Ants versus "Lions" and "Tigers"

My last post here chronicled predation on termites by ants in the wake of swarming events in my neighborhood. Today I shall turn the tables and demonstrate that ants are not immune to predators themselves. Antlions and tiger beetles are among the few predatory insects that kill and eat ants. Ants can bite, and either sting, or spray formic acid to defend themselves. One cannot blame a potential predator for avoiding that kind of trauma when ants are not much more than an hors d' oeuvres anyway.

Antlion pit of Myrmeleon sp. larva

While looking for tiger beetles in Lake Pueblo State Park, Colorado on March 18, I was surprised to find the funnel trap of an antlion larva in the middle of a game trail. Usually, the pitfall traps of antlions are clustered, and situated in sheltered areas like beneath a rock overhang, at the base of a tree, or other location where rain seldom if ever reaches them. Since the only genus of antlions in the U.S. that makes such traps is Myrmeleon, I knew that had to be the critter lurking at the bottom of the pit.

Antlion larva from Kansas

Buried just beneath the dusty sand was a single, chubby larva, studded with spines on various parts of its body, and with menacing sickle-like jaws. Nearly blind, the insect relies on its sensitivity to vibration to detect potential trouble or potential prey. When an ant or other terrestrial insect blunders into the antlion's steep-walled trap, the larva becomes alert and proactive. It may use those jaws to fling sand onto its victim, hastening its descent to the bottom of the funnel. The predator then grabs its prey and injects it with enzymes that paralyze it and begin the digestive process.

Adult antlion, Myrmeleon exitialis from Colorado

Antlions go through complete metamorphosis, so the larva eventually constructs a cocoon of sand and silk in which it pupates. An adult antlion, more than making up for its youthful ugliness with its delicate wings and slender body, emerges from the pupa at a later date.

Blowout Tiger Beetle, Cicindela lengi, attacking a harvester ant

The fate of ants in the jaws of an antlion may seem morbid, but it is still better than what happens to ants caught by adult tiger beetles. After two consecutive days of unsuccessful searching for tiger beetles closer to home in Colorado Springs, I finally found at least three Blowout Tiger Beetles, Cicindela lengi, on the afternoon of March 23. I was witness to their ability to swiftly dispatch lone worker ants with their huge, toothy jaws.

Open wide....

Most tiger beetle species are agile daytime hunters that haunt sandy habitats like the sandhill bordering the vacant lot where I found these specimens. The insects run quickly, stop, then run again. They fly a short distance if spooked by a potential predator. Their eyesight is keen, vastly more sensitive to motion than a person; but they focus slowly. They literally outrun their eyesight when pursuing prey, and must stop to refocus before rejoining the chase. This herky-jerky hunting strategy is still effective, and few insects spotted by a tiger beetle will live to tell the tale.

Off with its head!

Tiger beetles appear to have the speed and power to attack insects and other invertebrates at least as large as they are, but most of their victims are quite small. Ants seem to be near the limit of what they will take. They make short work of even the feisty Western Harvester Ants, Pogonomyrmex occidentalis, that are abundant in Colorado Springs. The jaws of the beetle quickly dismember the ant, leaving a trail of carnage around the beetle. The beetle's next victim may be a tiny, unidentifiable invertebrate it plucks from between sand grains.

Another C. lengi surrounded by the remains of its Formica sp. ant lunch

Most tiger beetle enthusiasts are fond of remarking that they are glad tiger beetles do not get any larger in size than they do. Indeed, I would not be prowling around dunes and beaches if there were even raccoon-sized tiger beetles in the neighborhood. Since they are much smaller than that, I recommend going in search of them. Their beauty and behaviors are sure to capture your curiosity and sense of wonder.

Predator and Prey: Ants versus Termites

My neighborhood walk in Colorado Springs the other day, March 25, was like strolling through living confetti at some points. All the local termite colonies were launching swarms of winged males and potential queens (alates as scientists call them). The frail creatures were not ignored by other animals, either, especially ants. Closer inspection of the swarms revealed three species of ants preying on them.

Alate subterranean termites (Reticulitermes sp.) swarming

Termite swarms are not an indication of the impending collapse of your home or any other wooden structure. Yet, that is the first thought that enters the mind of the average person witnessing the spectacle. Such is the power of advertising for pest control companies. Now, a termite swarm inside your home should probably be cause for alarm. Outdoors, subterranean termites like these Reticulitermes sp. are vital to the recycling of decaying wood. They nest in the soil, as their common name suggests, and forage for wood and other dry cellulose in contact with the soil.

The synchronous nature of termite swarms is a marvel. All colonies in a given area need to liberate their reproductive castes at the same time in order to prevent inbreeding, but I have no idea how they "decide" when to do this. The day before we had snow and high winds. The alates issue from the tiniest of cracks in the soil, like toothpaste from the tube, the better to avoid easy detection. Eventually, enough of the insects appear that their gauzy wings reflect the sun and give away their presence. Soldier termites, and workers, too, escort them out and see them off.

Alate termites with workers and soldier (center) escorts

Hundreds, if not thousands, of winged termites begin filling the air. Few will survive the alert eyes and hungry mouths of birds, lizards, and other predators. The early season timing of swarms may in fact be tuned to precede the emergence of reptiles and the arrival of migrant birds. Ants, on the other hand, are already on the prowl.

Worker Formica sp. ant carrying termite prey

Both ants and termites are social insects, so it is fitting they would be deadly enemies and, one would think, well-matched foes. Watching one swarm happen on the edge of a driveway, I began noticing the appearance of worker ants, Formica sp., crossing the driveway. Eventually I saw one toting a winged termite back to the nest. The ant's nest. More ants followed suit.

Pavement ants (Tetramorium caespitum) killing alate termite (bottom) and worker termite (top)

Turning my attention back to where the termites were emerging, I noticed something even more frightening. Tiny "pavement ants," Tetramorium sp., were killing both alates and worker termites right at the termite nest opening. Whereas Formica ants are a bit larger than the termites, the pavement ants were smaller than their prey. How they avoided the menacing jaws of the soldier termites confounds me.

Formica ants near the entrance to their nest, with prey

Just up the street I noticed heavy ant activity originating at the base of a brick-and-mortar mailbox pillar. These were Formica pallidefulva ants, but appeared larger than the other ones I saw previously. It soon became apparent that they were also taking part in the Great Termite Massacre of 2017. Most of them were carrying wingless alates, though.

Ants (Formica pallidefulva) with termite prey

Alate termites, once paired, shed their wings easily. Both pairs of wings have a weak spot that allows the termites to break them off so they can quickly seek cover. The male ("king") termite follows on the heels of his mate (queen) as they form a two-car train in search of a potential nest site. They must do so quickly if they are to avoid the marauding ants.

Dealate queen with her mate trailing her in a "train"

Whether the honey pot ants were taking dealate (wingless reproductives) termites, or just seizing winged individuals and breaking off their wings, remains a mystery. They are certainly easier to transport without those cumbersome wings.

Worker Formica sp. ant carrying termite prey

As I turned the corner to go home, I caught sight of yet another ant, possibly Formica podzolica. It, too, was carrying a defeated termite. The ant seemed at least somewhat disoriented, and I eventually lost track of it in the thick grass at the edge of the curb.

So, termites are both integral to keeping soils fertile with their decomposition activities, and also a bounty for many other organisms that depend on them for food when other insect life is less plentiful. Ants are the lion kings and wolf packs of the macroscopic landscape, keeping termites and other insects from overrunning the planet. The ants are not immune, though, and in my next post we see them on the other end of the predator-prey equation.

Note: Special thanks to James C. Trager for identification of the ant species.

The Maggot on the Rosebush: Aphid-eating Flower Fly Larvae

Gardeners cannot always be faulted for not understanding who their insect friends are. Entomologists have done a relatively poor job of advising the public on what garden insects are pests, and which are beneficial. It is especially problematic when you consider metamorphosis. You do not always know which larva corresponds to which adult, and whether both life stages are helpful or harmful. Case in point, larvae of flower flies (family Syrphidae), also known as "hover flies."

The overwhelming majority of flower flies in the subfamily Syrphinae are aphid predators in their larval stages. What you might easily mistake for just another flower- or foliage-munching caterpillar on your rosebush is probably one of these allies in your war on pests.

Killing an aphid!

Not that you would even notice them, as they can be incredibly cryptic, disguised as a discolored patch on the edge of a leaf, or a shed pollen cone on a pine tree....

Flower fly larva on pine needle

Female syrphid flies lay eggs in or near aphid colonies. The tiny larvae that hatch feed and grow, with three instars before pupation. An instar is the interval between molts. Despite its elastic appearance, the larva still has an exoskeleton that must be shed in order for the insect to grow larger. The final molt results in the pupa stage, a convex pear-shaped lump attached to a leaf, stem, or other substrate. The adult fly eventually emerges from the capsule-like pupa.

A little Allograpta sp. flower fly

Most adult syrphids strongly resemble wasps or bees, to the degree that they frequently fool entomologists. Like their hymenopteran models, the flies are capable pollinators of various flowers, visiting blossoms for nectar and picking up pollen in the process.

Adult female Syrphus sp. laying eggs in aphid colony

Flower flies can be recognized by their hovering behavior (few bees are capable of hovering, oddly enough), enormous eyes that meet at the top of the head in males, and nearly meet in females, and only one pair of wings to a bee's two pairs. Flower flies also have very short antennae in most cases, whereas bees and wasps have longer, thicker antennae, often "elbowed" where the first, long segment is connected to the remaining shorter segments.

A tiny Toxomerus sp. pollinating a flower

Lastly, while bees and wasps have chewing mandibles and sometimes a tongue-like arrangement of other mouthparts, flower flies have an extendable...."arm" tipped with a sponge-like pad. This organ is retracted under the fly's "chin" when not in use.

Adult Eupeodes or Syrphus sp.

Syrphid flies are among the most abundant of garden insects, especially conspicuous in spring and fall when aphid populations are at their peak. Watch for them and be careful not to accidentally kill their larvae when you are contemplating taking aphid control into your own hands. Between syrphid larvae, lady beetle larvae, and lacewing larvae, you may not have to do anything to keep aphids from reaching destructive numbers.

Another one bites the dust!

Sources: There are several excellent online resources about syrphids.
Rotheray, Graham E. 1993. "Colour Guide to Hoverfly Larvae in Britain and Europe," Dipterists Digest. No. 9. Sheffield, England: Derek Whitely and the Royal Museum of Scotland. 160 pp.
Flower Fly Survey of Los Angeles County
University of California Integrated Pest Management website on syrphids.
Texas A & M University website

Mini-mantises: Ochthera Shore Flies

Mantids (aka "praying mantises") are widely acclaimed for having the strongest grip among predatory insects, but many other insects have similar modifications to their front legs that afford them a vise-like purchase on struggling prey. Among the more unusual of these are shore flies in the genus Ochthera, found over most of North America.

I was delighted to discover some of these flies recently here in Colorado Springs, where they favor very shallow, trickling streams with algal mats and other debris they can run around on in search of other small insects.

Ochthera are small, only 4-5 millimeters in body length. They are squat and compact, with triangular faces and somewhat protuberant eyes. Their most obvious feature is the pair of front legs, with an enlarged coxa (segment connecting the leg to the thorax), greatly enlarged and muscular femur ("upper arm" if you will), and curved, blade-like tibia ("forearm" comparison to a person). The tarsi ("feet") are of normal appearance. The forelegs are thus raptorial, meaning heavily modified to sieze prey. Spines and tiny teeth on the inside of the femur help anchor the victim between femur and tibia.

The flies easily overpower other small insects such as midges, mosquitoes, and leafhoppers that alight on the shore or the surface of the water. They can also unearth midge larvae from the muck along the shore.

Watch one of these flies and you will see it periodically "stretch," reaching out, flexing, and waving those front legs. This may be a threat display directed at other members of its own species, or a means of recognizing each other and avoiding cannibalism (Simpson, 1975). Females may literally lash out at males attempting to mate with them. Males attempt to mount females from the rear, jumping on top of them and gripping the female's "shoulders" if they are not rebuffed. He sets the mood by rapidly tapping the sides of her abdomen with his hind feet. Actual mating can last at least five minutes, at least in one species (Deonier, 1972).

Mated females lay eggs singly, usually on dead, water-logged, or partly submerged grass stems at the shore or in the shallows. Larvae of Ochthera are aquatic or semi-aquatic, and likewise predatory; they feed mostly on midge and mosquito larvae that they coil around like a snake constricting a rat. They have mouthparts that penetrate the exoskeleton of their prey and feed on soft internal tissues. Larvae progress through three instars (an instar is the interval between molts), before pupating. The pupal stage is also aquatic, equipped with breathing tubes. The larval stages last an average of 7-11 days, the pupal stage about 7-10 days. Egg to adult thus takes about 16-21 days, at least under laboratory rearing conditions.

Look for Ochthera adults from the end of March through the end of October in appropriate habitats. There are thirteen species known for North America, collectively distributed over most of the continent.

Sources: Deonier, D.L. 1972. "Observations on Mating, Oviposition, and Food Habits of Certain Shore Flies (Diptera: Ephydridae)," Ohio J. of Sci. 72(1): 22-29.
Simpson, Karl W. 1975. "Biology and Immature Stages of Three Species of Nearctic Ochthera (Diptera: Ephydridae)," Proc. Entomol. Soc. Wash. 77(1): 129-155. This is an excellent, well-illustrated paper.
Winkler, Isaac. 2011. "Insect of the Week - number 57," Insect Museum, North Carolina State University.

Long-legged Flies

Happy “Fly Day Friday,” everyone. Long-legged flies in the family Dolichopodidae include those little, bright metallic green flies you see darting over leaves in sunny spots; but they also include flies that run up and down tree trunks, or skate across the surface of puddles. The diversity of this family is almost as staggering as the Syrphidae, Bombyliidae, and other fly families that are more familiar.

The Condylostylus species imaged above, from Skokie, Illinois, is the typical dolichopodid we normally see in the garden, along forest edges, and similar habitats. Like all longlegged flies they are predatory on other small insects. It can be maddeningly difficult to get a good image of one because the flies aren’t that large to begin with, hardly ever stop moving, and can be sensitive to the pre-flash on your camera such that you wind up with either an empty frame, or an out-of-focus fly in mid-air as it departs.

Condylostylus sp. with prey

Dolichopodids range in size from barely one millimeter to “giants” of ten millimeters. Most are five millimeters or less. They are usually metallic green, copper, or bronze, though many species are muted rather than brilliant.

Hydrophorus sp. pair, Colorado Springs

What is truly astounding is the diversity of this family. There are nearly sixty (60) genera in North America north of Mexico, with about 1,300 species. It is difficult enough to identify a given specimen to genus, but species ID generally requires examining the male genitalia. Not that the male’s “man parts” are not obvious. His claspers and other, um, paraphernalia are easily seen as forward-protruding appendages at the tip of the abdomen (curled beneath the abdomen).

The front “feet” (tarsi) of males of most Dolichopus species are adorned with special scales that may resemble tiny flags. These ornaments are used to display to females in complex courtship dances.

Hydrophorus sp., Pueblo Reservoir, Colorado

Besides looking for these flies on foliage, keep an eye out for them on the water, too. Hydrophorus species skate across the surface of puddles, intermittent streams, and near the shores of lakes and reservoirs where they behave much like water striders. Members of the shorter-legged genus Dolichopus can also be seen on the surface film. The adults of these flies are even adept at preying on mosquito larvae, nabbing the “wrigglers” when they ascend for air.

Liancalus genualis, South Deerfield, Massachusetts

Longlegged flies do not have beak-like mouthparts like robber flies or dance flies, but instead have a lower “lip” modified into an extendable appendage and equipped with a pair of flaring, opposable lobes that can crush a victim or tear it to pieces. Hard to believe these diminutive, delicate insects are really quite vicious predators.

The “woodpecker” flies in the genus Medetera are commonly seen on the trunks of trees, literally standing on tiptoe in a seemingly awkward posture. They still have the agility of their cousins, I assure you.

Medetera sp., Redondo Beach, California

As far as is known, dolichopodid maggots are also predatory. Most are aquatic or semi-aquatic, but the larvae of at least some Medetera species roam the galleries of bark beetles, feeding on the beetle grubs. The larvae of most species, however, remain a mystery.

It is impossible to do justice to these remarkable flies in a blog post, or even a book, but I encourage you to do a double-take the next time you see an unfamiliar little fly. It may well be a dolichopodid, and what you observe could easily yield new knowledge.

Tachytrechus angustipennis(?), Colorado Springs

Sources: Bartlett, Troy, et al. 2004. “Family Dolichopodidae – Longlegged Flies,” Bugguide.net
Marshall, Stephen A. 2006. Insects: Their Natural History and Diversity. Richmond Hill, Ontario: Firefly Books Ltd. 732 pp.
McAlpine, J.F., B.V. Peterson, G.E. Shewell, H.J. Teskey, J.R. Vockeroth, and D.M. Wood (coordinators). 1981. Manual of Nearctic Diptera Volume 1. Ottawa: Agriculture Canada. 674 pp.

Spider Sunday: A Common "Indoor" Spider

At this time of year, there is one spider that is commonly encountered indoors in the eastern United States and southeast Canada. It has a bi-colored body that makes it conspicuous and different from most other spiders one is likely to see around their residence. Trachelas tranquillus, is sometimes known as the “Broad-faced Sac Spider,” a member of the family Corinnidae.

This is a spider of average size, adult females measuring 7-10 millimeters in body length, males 5-6 millimeters. It occurs from Nova Scotia and Minnesota south to Kansas, Oklahoma, and northern Georgia, preferring deciduous woodlands. In nature, specimens are often found in retreats fashioned from curled leaves; or they are seen occasionally under stones.

I have seen this species hunting actively at night, prowling around porch lights where it may be hunting various insects attracted there. Trachelas does not spin a web, but does lay down draglines to help secure itself during climbs. Females probably also impregnate their draglines with pheromones (scents) so that males can track them down.

© Ken Lebo 2012

Mating usually happens in summer and early fall, after both genders have matured (nice images on the highlighted link). Females create a lens-shaped egg sac, the bottom flat against a substrate and the top slightly convex. The whole package is roughly ten millimeters long and usually attached beneath loose bark, or under a rock.

Besides killing live prey, Trachelas may scavenge on dead insects. Perhaps this is why it prospers when other spiders have either perished or gone into hiding in autumn. This scavenging habit may also influence the outcome in those rare instances when the spider bites a human. Secondary infections from its bite have been recorded, originally interpreted incorrectly as caused by the spider’s venom.

© Sarah Rose

The fact that Trachelas hunts regularly in and around homes and other buildings means it is more likely to have interaction with people. Still, verified cases of bites are infrequent, and usually result in only localized pain and swelling. People sensitive to arthropod venoms, or prone to allergic reactions, should seek medical attention for any arachnid bite (or sting in the case of scorpions).

Further complicating this picture is the confusion of Trachelas with another spider that is completely innocuous, though more intimidating. The Woodlouse Hunter, Dysdera crocata, is a specialized predator of woodlice, known commonly as “sowbugs,” “roly-polies,” or “pillbugs.” This species has exceptionally long jaws and fangs it uses to turn over its armored prey. While it looks dangerous, it is not.

Dysdera crocata © Nick Richter 2010

Dysdera is not native to North America, having been introduced from Europe at some point in our history. It has also become accustomed to prowling around human dwellings, so may be found indoors. It does not climb as well as Trachelas, however, and in my experience the Woodlouse Hunter prefers to hug baseboards.

Dysdera crocata © Sarah Rose

I encourage my readers to appreciate all spiders, but also act responsibly. It is a good idea to try and exclude spiders from entering your home and workplace by repairing worn weatherstripping on doors, mending holes in window screens, and sealing any cracks and crevices that could offer passage for insects and arachnids. Be careful when bringing objects indoors from outside, too, like firewood, gardening implements, children’s toys, and shoes and clothing left outdoors overnight.

Sources: Cox, Shelly. 2011. “Ground Sac Spider,” MoBugs blog.
Eaton, Eric R. and Amanda Howe. 2012. “Trachelas tranquillus (Ground Sac Spider),” Spiders.us.
Jacobs, Steve. 2002. ”Broad-faced Sac Spider,” Penn State University fact sheet.

Spider Sunday: Apache Jumping Spider

Jumping spiders in the family Salticidae are arguably the most colorful of all spiders, often quite conspicuous despite the fact they are usually rather small in size. Here in North America, the genus Phidippus includes some of our largest jumpers. I have found one bright species to be quite common in recent weeks here in Colorado Springs. Phidippus apacheanus is the Apache Jumping Spider, if I can assume it has that common name.

Just yesterday, September 8, I found two specimens on two separate sunflower plants. They appeared to be basking, but more likely they were waiting for potential prey to come within pouncing range. The male, black on the bottom and legs and bright orange on top, may mimic the velvet ants that also frequent sunflowers. Females have a dark dorsal stripe that runs up the middle of the abdomen.

These are not the largest of our jumping spiders, but still bigger than most salticids. Males range from 5.2-10.6 mm, while females measure 7.1-13.3 millimeters. At least one of the specimens shown here may also be immature, one molt or so away from adulthood. Mature individuals can be found at almost any time of year, though males in particular are most common in autumn.

Despite the western-sounding name, this species ranges over most of the United States save New England and the Pacific coast states. Most records do come from the southern half of the U.S. and into Mexico and Cuba.

The habitat preferences for the Apache Jumper may also explain its abundance in certain regions. It is most often found in grasslands, prairies, plains, and dry fields, up to 6,000 feet or so in elevation. Look for it on shrubs, perennials, cacti, and yucca where it prowls for insect prey. Even wasps can fall victim, like the little crabronid captured by this male on August 27.

Females of Phidippus apacheanus fashion egg sacs in protected niches, such as beneath the bark on oak logs. There they guard the sac and the spiderlings that emerge from it.

This species occurs in areas where other, similar species of Phidippus can also be found, so you can’t always rely on color pattern alone to identify it. The only way to confirm which species a given specimen belongs to is to put it under a microscope and examine its external genitalia. You still might not be able to reach a conclusion if the specimen is immature.

While I am always curious as to exactly what I am taking an image of, I can still delight in the colorful nature and vibrant personalities of jumping spiders. Their alertness is engaging (if not maddening when they dodge to the other side of a stem), and suggests a level of awareness and intelligence that most other arthropods do not possess. Happy spider hunting.

Source: Edwards, G.B. 2004. “Revision of the Jumping Spiders of the Genus Phidippus (Araneae: Salticidae),” Occasional Papers of the Florida State Collection of Arthropods vol. 11. 156 pp. (available for sale here).

Spider Sunday: Whitebanded Fishing Spider

When Heidi and I went to South Carolina early last May, one of the animals on my “hope to see” list was the Whitebanded Fishing Spider, Dolomedes albineus. It took until the last day of our trip, but I finally found one at the Whack-a-Mole Natural….Wait, that’s not right. The Whatchamacallit National….No….Ah, yes, the Waccamaw National Wildlife Refuge.

The spider was sitting on a piling supporting a floating dock on the Pee Dee River. This is not a small spider. Mature females measure about 23 millimeters in body length (just under an inch). Males average 18 millimeters. Ordinarily, the spider’s mottled gray pattern blends perfectly with lichen-spotted tree trunks where it waits in ambush for an unsuspecting insect or other small animal to wander within striking range.

This particular arachnid perceived motion very well. I ended up chasing it around the piling before it finally settled down. Oddly, it did not bolt, but simply sidled slowly to a new position on the piling. Creepy. Creepy in a creeping, stealthy, smart kind of way.

The white band that gives this spider its common name is the area immediately under the eyes and above the chelicerae (jaws). Maybe it should be called the “whitefaced fishing spider” instead. Sometimes the entire carapace (dorsal surface of the cephalothorax) is white, save for a black spot in the center. Indeed, the color pattern of this species is highly variable. Some individuals are even a mossy green color with darker markings.

This is a fishing spider that really is most common along the edges of aquatic habitats, especially the cypress swamps of the southeast U.S. Its geographic range is from Florida inland and north to the Appalachian Mountains of North Carolina, as well as the Mississippi River basin as far north as Kentucky and southern Missouri.

Not much is known about the life history, habits, and behavior of this species, so your own observations might lend something new to science. At least one researcher, James Carico, noted that adults sometimes congregate in tree holes and crevices, perhaps in a “mating swarm,” though that would be a rare behavior for most arachnids (Carico, 1973).

Like all pisaurids, D. albineus females carry the egg sac in their jaws before eventually creating a “nursery web” amid foliage, bridge beams, or other situations. The female then guards the egg sac and the spiderlings that emerge from it. Once the spiderlings have their first molt outside of the egg sac, they disperse. Their mother then resumes hunting, having fasted during her parental duties.

I consider myself lucky to have seen this magnificent spider, and I hope that you will add it to your own “must see” list of arachnids. You do have one of those by now, right?

Sources: Carico, James E. 1973. “The Nearctic Spiders of the Genus Dolomedes (Araneae: Pisauridae),” Bull Mus Comp Zool 144: 435-488.
Gaddy, L.L. 2009. Spiders of the Carolinas. Duluth, Minnesota: Kollath+Stensaas Publishing. 208 pp.
Howell, W. Mike and Ronald L. Jenkins. 2004. Spiders of the Eastern United States: A Photographic Guide. Boston: Pearson Education. 363 pp.

Spider Sunday: Goldenrod Crab Spider

There are few terrestrial invertebrate animals that can change color at will, but females of the Goldenrod Crab Spider, Misumena vatia, are among them. This chameleon-like quality is just one fascinating aspect of the life of this amazing arachnid.

I should say that while the spiders can turn from white to yellow, or vice versa, this transformation is not instantaneous. It takes from one to twenty days to achieve. The result is quite miraculous in that the spider will end up virtually indistinguishable from the flower upon which it sits. Many a time I have watched one of these spiders materialize from blossoms right before my eyes.

This flower disguise helps these patient ambush hunters to capture prey consistently. The females need to be efficient because their lifespan is relatively short and they need to produce a good clutch of eggs to ensure a future generation. A female puts on about 85% of her body weight after she matures. Her eggs account for most of that mass, of course.

Despite the fact that spiders have an exoskeleton, the cuticle is incredibly elastic. Her abdomen can easily expand to accommodate a large meal and/or her developing ova.

The flower crab spider is small but mighty. Adult females measure 6-11 millimeters in body length, but their strength exceeds what you would expect. Misumena is capable of taking down some impressive, well-defended prey like the honeybee in the above image. I actually found the spider by noticing the awkward posture of the honeybee first. The Boulder Raspberry blossoms were certainly getting a lot of attention from pollinators, so the spider picked a prime hunting ground (on Cheyenne Mountain near Colorado Springs, Colorado).

Even more stunning, I came across another specimen, this time in yellow phase on a Golden Banner flower, that had seized a large Chryxus Arctic butterfly (Teller County, Colorado at an elevation of over 8,000 feet). Arctic butterflies never rest with their wings open, so I knew something was up….

The males of Misumena vatia are certifiable wimps compared to their mates. The masculine gender measures a mere 2.5-4 millimeters at maturity. He is skinny and leggy compared to the voluptuous female, and he has an entirely different color pattern. Not strong enough to secure large meals, he may even settle for eating flower pollen. He matures faster than the female, and as an adult will wander constantly in search of prospective mates.

Mated females eventually produce an egg sac that is usually wrapped in a folded leaf. She guards her brood religiously and will not feed until the spiderlings emerge and disperse. Note the gaunt appearance of the female below, standing guard over her bundle of eggs. The “pleats” on her abdomen reflect the elastic nature of her exoskeleton.

Misumena vatia is a member of the crab spider family Thomisidae; it is a common and widespread species ranging across the entire northern hemisphere including North America, Eurasia, and northern Africa. Female spiders may be yellow or white, with or without rosy stripes on their flanks. It takes a sharp eye to spot them, but I can just about guarantee you have some in your neighborhood somewhere.

Want to know more? Almost every aspect of the natural history of this species has been studied in detail, a fact reflected in the numerous scientific papers generated over the decades. An entire book has even been written about it: Predator Upon a Flower: Life History and Fitness in a Crab Spider, by Douglass Morse (Harvard University Press, 2007). You will also find a more succinct yet still captivating summary at Spiders.us, courtesy of Mandy Howe’s diligent research.