Saturday, September 23, 2017

Walking on water

Scanning a sunlit pond floor for crayfish, I was distracted by seven dark spots gliding in a tight formation. Six crisp oval shadows surrounded a faint, less distinct silhouette. The shapes slid slowly and then, with a rapid motion, accelerated before slowing to another glide. I can remember seeing this pattern as a child, in my first explorations of pond life.

Water strider shadows are far larger than the insects casting them. To visualize the surprising proportion of legs to body, it may help to think in human scale. For mathematical simplicity, picture a six-foot-tall man lying flat on the water surface. Imagine that attached near his hips he has a pair of seven-foot-long, stick-skinny legs pointing back at a 45 degree angle. Just forward of these spindles he has another pair pointing forward at a 45 degree angle; these are nine feet long. A pair of three-foot-long arms point forward and each has a single claw protruding from the palm.

The legs are long for good reason; they distribute body weight over a wide area, and aided by water repellent hairs, allow the insect to coast across the water’s surface tension. The minute leg hairs are densely packed and each has many air-trapping surface grooves. According to the Chinese scientists who discovered the grooves, water striders displace enough water to float up to fifteen times their own body weight. This extreme buoyancy is enough to keep the water strider’s body high and dry above the water, even during rainfall and choppy conditions.

Because the insects literally walk on water, some call them “Jesus bugs.” When fish or backswimmers approach, the water striders are well positioned to make an aerial getaway. Their super buoyancy means that they can use their long legs to jump straight up from the water surface, and once airborne, they can spread their wings (yes, they have wings) and fly to safer haunts.

Slow motion video reveals how water striders move. The longer middle legs sweep back rapidly like oars, pushing against the surface tension to drive the insect forward. Human rowers lift their oars out of the water on the recovery stroke to reduce drag, and rapidly moving water striders do the same thing. However, when moving more slowly, they drag their middle legs forward along the water surface. The rear legs trail and change angles like twin rudders steering the insect towards food, or mates, or away from hazards.

All the while, the front legs rest on the water surface just forward of the insect’s head. Theirs is a murderous function, allowing the water strider to find and seize its next meal. Subtle ripples made by surfacing aquatic insects including mosquito larvae, or struggling terrestrial insects on the water surface function like tugs on a spider web, leading the water strider to its prey. The single-clawed forelegs grapple the prey while the insect’s piercing mouthparts stab through the cuticle, consuming bodily fluids as if through a drinking straw.

To see this first hand, my Saint Michael’s College students and I dropped a few large carpenter ants onto the water surface of some ponds in Winooski. It took only seconds for a water strider to grab the first ant. Others were rapidly scooped up and carried off. A braver student dunked a yellow jacket, trapping her in the surface tension. The water striders investigated but took a pass on that risky meal. The yellow jacket climbed out on some vegetation a little the worse for wear.

My students and I were also curious to see if the insects were faithful to particular pools or if they moved around. We used paper correction fluid (“Wite-Out”) to mark a dozen water striders and released them where we caught them. The following day, we found marked water striders in their home pool, but also in pools upstream and downstream. We frequently observed water striders fighting each other. Perhaps territoriality and competition drives them to seek other living space?

As summer arrives, I have noticed that the water striders are back in force from their winter hideouts among the pond-side leaf litter. I’d welcome a little sun any day now so that their spectacular shadows may also return.

Declan McCabe teaches biology at Saint Michael’s College. His work with student researchers on insect communities in the Champlain Basin is funded by Vermont EPSCoR’s Grant NSF EPS Award #1556770 from the National Science Foundation.


This article was written for Northern Woodlands Magazine's Outside Story and first published on June 12th 2017

Download the Article © by the author; this article may not be copied or reproduced without the author's consent.

Sunday, September 3, 2017

Beetles and ballet


The tree dance with flowers awaiting pollination. 

Seated with my children on folding chairs at Philo Ridge Farm in Charlotte; strains of Vivaldi pierced the evening air.  There’s nothing quite like live music.  But we were not there just for the music.  A pair of dancers pirouetted onto the ‘stage’, or should I say ‘lawn’.  An expectant hush moved through the audience as the dancers met, and exchanged glances of feigned indifference for the beginning of their performance. Strangely, their gazes seemed focused behind their partner’s backs. 
The performers turned and parted, the side-long view revealing unusual costume choices for classical ballet.  Each had a flickering, glowing, insect-like abdomen extending from beneath beetle-esk wings. This was Farm to Ballet, and we were being treated to ‘The Firefly Dance’.
Perhaps only in Vermont, would a ballet company take to the fields, contributing to the charm that keeps us all here. The dancing was amazing as ballerina and ballerino circled and posed, all the while, each examining the other’s flashing light pattern.  Initially lack of synchrony between their abdominal lights seem to cause repulsion between the dancers.
Real fireflies are innocuous beetles, easily overlooked during daylight hours. Their larvae eat insects and snails and may well be important pest control agents.  They are found in vegetation, leaf litter, and along the soil surface where they are frequently pit trapped by Saint Michael’s College student researchers. 
It is only at night that fireflies come into their own and truly capture the imagination.  The adult beetles use flashing light pulses and larger eyes than those of many beetles to communicate with and attract mates.  Males flash as they fly a few feet off the ground, and choosey females sit in darkness returning the male’s signal only when a particular attractive flash pattern tickles their fancy.  Female fireflies can afford to be picky, at least early in the season when they may well be outnumbered two to one by males.  Mark Branham and Michael Greenfield used computer controlled lights to demonstrate that females of one firefly species really preferred fast flashing males; in fact they responded best to flash patterns that were even faster than most male beetles could ever achieve.
Because fireflies use light to find mates, biologists have frequently expressed concern that light pollution might disrupt their mating habits.  Anyone who has made the mistake of leaving the lights on with a window open can confirm that artificial lights attract insects; entomologists rely on this quirk of insect biology to trap study specimens.  Firefly numbers seem to have declined in recent years as light pollution has increased, but the precise link between fireflies and lights was more clearly established this year when Kevin Costin and April Boulton demonstrated that even a single powerful light placed at a field site could reduce firefly flashing by half. 
If the Farm to Ballet dancers were at all concerned about light pollution, they did not mention it to me.  But creative director Chatch Pregger did confirm my perception of the developing firefly dance.  As he danced with his partner Avi Waring, their lights gradually changed from random, asynchronous flashes, to tightly choreographed patterns that flashed in unison.  The ballerina’s initial distain for her partner was replaced by harmoniously flowing parallel moves and lifts as they simultaneously achieved synchrony of light flashes and choreography that captivated their audience.
According to Pregger, the light flashes controlled remotely by an off-stage cast member were designed to gradually synchronize by the end of the dance.  The synchronous flashing lights mimic the patterns used by the same firefly species studied by Branham and Greenfield.  Females of Photinus consimilis, respond to the males using flash patterns that are dimmer than, but remarkably similar in frequency and duration to those of the males.  If the female sends an appropriate signal to the male, they achieve their own form of highly evolved choreography.
As the evening drew to a close and the crowd filtered out, the subtle sparks of real fireflies continuing their evolutionary journey went largely unnoticed by dancers and audience members.  With summer over, dancers have abandoned the fields in favor their South Burlington Vermont studio.  As the Farm to Ballet troupe develops the following season’s choreography, next year’s firefly larvae have burrowed into the soil following choreography that has sustained them over eons. 

Saturday, April 1, 2017

Flashlight on a stick


Figure 1.  The truly amazing Flashlight on a stick
Yes folks, I have finally broken into the invention market.  After several minutes of research and development, I bring you, Flashlight on a stick (Figure 1).

Flashlight on a stick comes with two, count them, TWO revolutionary components: a shiny blue impact-resistant flashlight lovingly constructed from cheap flashlight-grade aluminum, and a high-quality, 100% organic, high-fiber stick.  Flashlight on a stick can be your third hand on those occasions when you are tempted to go against the advice of your dentist by holding a light in your teeth.  You can use it to illuminate specimens on a microscope (not provided), or as a handy door stop or paperweight.   

Flashlight on a stick has three settings, on, off, and out of batteries.  Because of it's unique single screw design, Flashlight on a stick can rotate through a full 360 degrees allowing you to deliver cool LED illumination wherever it is needed.  You can shine a light on impossible-to-reach-but-at-least-you-can-now-see-them items under your desk, or right up your nose.

You can have flashlight on a stick for 24 easy payments of $12.99....or you could just make your own.

Figure 2.  Light in use with microscope
But seriously folks, I needed a way to put light on specimens on a microscope (Figure 2) for a program in the woods far from electrical outlets.  Simple is sometimes best.  The flashlight cost $0.99 from an Ebay vendor; the mounting bracket cost $1.25....and I had some 2.5" by 1.5" lumber laying about the place.  The single screw mounting bracket really is convenient so you can direct the light anywhere.  I could see using this for camping.  I cranked out 8 of these in about half an hour and I'll probably use them until I retire.

Saturday, January 7, 2017

Cloudy with a chance of flies

Clouds of tiny insects, rising and falling hypnotically along lake shores, contribute to the ambiance of warm summer evenings. My recent bike ride was interrupted by a lungful of this ambiance.

If you find yourself in a similar predicament, you might wonder what these miniscule flies were doing before being swallowed, where they came from, whether they bite, and whether we need these interrupters of peaceful lakeside jaunts. We’ll get to these questions, but first, let me say that as an ecologist, I find these insects to be among the most fascinating and important freshwater invertebrates.

Non-biting midges, also called chironomids, are most conspicuous when they hover in swarms near water. Not to be confused with the no-see-ems or biting midges maligned by Thoreau, they constitute a diverse family found on every continent. Two midge species are the only known insects in Antarctica. One Antarctic species lacks wings entirely and is therefore, I suppose, at little risk of death by human inhalation.

Whether Earth-bound or in flight, mating is the reason for midge swarms. Newly emerged adults have a short time to find mates, and dense swarms function like singles bars.
My clumsy encounter with a nuptial swarm did not make much of a dent in local midge numbers. They are abundant. They’re also hyper-diverse, with more species in this one true fly family than in all the families of stoneflies combined. Entomologists have described more than 5,000 species and are regularly called upon to come up with scientific names for newly discovered species. Dicrotendipes thanatogratus, a midge named for the Grateful Dead (thanatos is Greek for “dead” and gratus is “grateful” in Latin), is one example.

With so many species, it’s not surprising that non-biting midges thrive in all sorts of habitats. Saint Michael’s College students and I have found them in every stream, pond, and lake we have sampled, and they often exceed 50 percent of the insects we capture. In ponds and deep river-silts, bright red midges called bloodworms use skin-bound hemoglobin to scavenge every trace of oxygen from their stagnant habitats. Dr. Richard Jacobsen studied a midge found only on the backs of mayflies; its life cycle synchronizes perfectly with that of its bigger host.

Non-biting midges are also diverse in their culinary predilections. They eat nearly every conceivable foodstuff; they can be scavengers, herbivores, predators, or parasites. One species, Metriocnemus knabi, feeds exclusively on insect parts in pitcher plants in northern bogs. There are abundant midges grazing algae in salt marshes, consuming leafy detritus in tree holes, and they may well be scavenging from the rain water in the gutters of your house. These insects are essential in the aquatic food webs that support fish populations, and anglers seek to replicate their delicate forms to lure their catch.

Like many insects, midges grow through a series of larval stages. Slim, legless, translucent larvae hatch from eggs laid in gelatinous masses. They grow quickly and become too big for their exoskeletons. These split, revealing softer exoskeletons that stretch and harden around their bodies. In streams, where I do much of my research, discarded exoskeletons accumulate behind rocks and logs. Sieving exoskeletons from stream froth is a little like panning for gold. Much information can be coaxed from these discarded shells. Cleaner streams host more midge species and certain species are never found in polluted streams.

After four rounds of growing and shedding, non-biting midges enter a pupal stage. They may appear somewhat static, but each pupa is a hive of cellular activity. Cells migrate and rearrange, forming compound eyes, six legs, and in most species, a pair of wings. After a few days, the pupae split and adults emerge. Some midges hatch only at certain times of day and the rhythm of a stream can be followed by sampling drifting pupal skins through the day.

The clouds of adult flies are a food source that moves from aquatic to terrestrial food webs, sustaining the swallows and bats that keep real pests in check.  Non-biting midge swarms will persist as long as the weather is warm enough for fly muscles to flap fly wings. Some species hatch early in the season, some later. There are species that hatch once per year; others can produce two or more generations in a season.

So when you find yourself in a swarm of insects this September, try to appreciate the romance. Perhaps the knowledge that fly love is in the air will make up for the occasional fly in your eye. Or in your mouth. Or snuffed right up your nose!

Declan McCabe teaches biology at Saint Michael’s College. His work with student researchers on insect communities in the Champlain Basin is funded by Vermont EPSCoR’s Grant NSF EPS Award #1556770 from the National Science Foundation.
This article was written for Northern Woodlands Magazine's Outside Story and first published on September 4th 2016
The photograph of an adult male midge was downloaded from Wikimedia Commons under a CC BY-SA 3.0 Creative Commons license.
Download the Article © by the author; this article may not be copied or reproduced without the author's consent.

Tuesday, April 26, 2016

Under the Water, December’s Peak Leaf Season


Pteronarcys.jpgBy December, foliage season is long over for us humans, but it’s peak season under the water. Last month, as the last bus of tourists departed for home, fallen leaves accumulated in our streams and rivers, starting a process that’s critical for the nourishment of everything from caddisflies on up the food chain to eagles and even people. In fact, most of a New England stream’s food supply originates in the form of fallen leaves.

The bright yellow and red piles that accumulate on river rocks and fallen branches are not nearly ready for consumption by discerning invertebrates. The witch’s brew of natural chemical compounds that discourages insects from eating green leaves on trees, can be just as repellent to creatures that scavenge freshly fallen leaves under water.  First, cold water must leach out those chemicals. Imagine the process as soaking and re-soaking a teabag. During this period, the leaves are also colonized by microscopic organisms. For a hungry invertebrate, the cleansed layered leaves, covered in fungi, bacteria, and algae, make a sandwich of which Dagwood Bumstead could be proud.

If all leaves were created equal, then the river food supply would consist of a brief crop polished off by whatever ravenous insect species got there first. But of course not all tree and shrub species lose their foliage at exactly the same time, and their leaves decompose at different rates. Some are tough, leathery, and laden with toxins. Certain laurel species can release so much cyanide that entomologists have used them to kill study specimens. Other species, such as linden, are comparatively soft and become an early underwater food source. Oaks and beech trees hold onto their tough leaves late into the season and when they finally fall, they are slow to reach an edible condition.


Variability in the timing of leaf fall, and in the rates at which leaves become palatable, means that edible leaves are available for most of winter. This is also the season when much aquatic invertebrate growth occurs.  A caddisfly species called Pycnopsyche gentilis acts like a chronicler of the leaf supply.  In fall and early winter, its larvae cut disks from leaves, and use silk to make and line pencil-diameter cases in which they live. In early spring, as leaves become scarce, and the larvae keep growing, they add to their cases using large sand grains.  This is why one can sometimes find cases with leaves at the back end and sand grains at the front.

Although fish aren’t typically leaf eaters, they nonetheless rely on the underwater foliage season. Cranefly larvae and stoneflies, fattened up on leaves, are protein-packed snacks for hungry trout, salmon, and bass.  Without invertebrates, fish would go hungry.  Without some knowledge of invertebrates, few anglers would know what to put on a hook to lure a spectacular brook trout.

Cleanest streams host most invertebrate species and simply counting the number of species can be the basis for an interesting study. For example, each fall, I visit forested and urban streams with Saint Michael's College biology students.  This year we found more than 20 species in Browns River, downstream from Mount Mansfield State Forest.  Centennial Brook drains South Burlington neighborhoods and parking lots, and hosts fewer than half that many invertebrate species. Browns River macroinvertebrates include clean-water loving giant stoneflies, and an assortment of mayflies. I have yet to meet a Centennial Brook stonefly because the community is dominated by midges, craneflies, and a particularly tough caddisfly that makes its living by filtering particles from the water.

A view into the world of submerged invertebrates is just a bunch of leaves away.  You can easily lift an intact chunk of leafy habitat from a streambed for study.  Equipment can be as simple as a basin of stream water. Drop a handful of streambed leaves into the basin and observations can begin. Rinse and remove the leaves one at a time to reveal the small creatures living among them.

Declan McCabe teaches biology at Saint Michael’s College. His work with student researchers on insect communities in the Champlain Basin is funded by Vermont EPSCoR’s Grant EPS-1101317 from the National Science Foundation.
This article was written for Northern Woodlands Magazine's Outside Story and first published on December 14th 2015
The photograph of a stonefly was downloaded from Wikimedia Commons under a CC BY-SA 3.0 Creative Commons license.  Download the Article

Saturday, January 30, 2016

Zebra Mussels


Invasive species have earned their bad reputations. English sparrows compete with native birds from Newfoundland to South America. Australian brown tree snakes are well on their way to exterminating every last bird from the forests of Guam. And I don’t think anyone can fully predict how Columbia’s rivers will change in response to drug lord Pablo Escobar’s escaped hippopotamus population.

While our climate protects us from rampaging hippos, the Northeast has plenty of exotic species in its waterways, including some that cause serious damage. Zebra mussels are possibly the most familiar of these. They were first discovered in Lake Champlain in 1993 by a precocious 14 year old, Matthew Toomey, who recognized one based on an identification card he’d received at school. Since then, the mussels have spread throughout the lake and their effects have been well chronicled. They kill native mussels; coat surfaces with razor-sharp shells; foul anchor chains; block water intake pipes; and steal plankton and other food from native fish.

With all of the negative press regarding the species, you might find it jarring to read anything positive about zebra mussels, particularly anything written by a biologist. Discussing positive effects of invaders is practically taboo. We don’t speak ill of the dead; we never praise invasive species. I’m certainly not advocating zebra mussel propagation, but like them or not, they are here to stay. These mussels are an important part of European ecosystems, and it’s interesting to consider what native organisms benefit from their presence.

Zebra mussels are voracious filter feeders. A single mussel can suck a liter of water through its body daily. All of this filtration removes plankton and particles from lake waters, but these particles don’t just disappear. The phrase immortalized in Minna Unchi’s children’s book Everyone Poops applies. Along with excrement, unpalatable particles rejected by zebra mussels are mixed with mucus and dropped on the lake floor. Mussel excrement and mucus might not sound appetizing, but it’s a smorgasbord for lake floor invertebrates and fish.

In addition to covering rocky surfaces, zebra mussels often carpet lake floor sand and silt. Formerly soft sediments that provided foraging grounds for sturgeon and other fish can become a tangled mess of living and dead mussels several inches thick. Not surprisingly, fish such as log perch, bullhead, and sculpins have difficulty finding their insect prey amongst the clutter of shells layered over their sandy habitats. When given the choice, juvenile sturgeon avoid zebra mussels and spend their time on sandy or rocky areas.

What’s bad for these predators may be good for their prey. To figure out just how good or bad zebra mussels could be for Lake Champlain invertebrates, we ran experiments under 30 feet of water in sandy areas of Appletree Bay. When my colleagues Ellen Marsden, Mark Beekey, and I fenced off lake floor patches with and without zebra mussels, twice as many invertebrates colonized areas with zebra mussels. More species also moved in. After a month, the number of species in experiments with added mussels doubled and included some species more typical of rocky lake floors. Nooks and crannies between zebra mussel shells seem to act like very small, natural shark cages that protect tiny insects from hungry fish. And when we placed insects and fish in aquariums, far more invertebrates survived with zebra mussels than without.

On balance, I would rather have a lake without zebra mussels than with them. But unless ways are found to eliminate them, it will remain important to understand how they affect native species. In Lake Champlain, the zebra mussel population grew rapidly and has since fallen below peak numbers, as often happens with this species in a new location. This month, for the first time in recent years, we pulled up a lake floor sample in Burlington Bay that entirely lacked zebra mussels. Perhaps we are reaching a new equilibrium?

Declan McCabe teaches biology at Saint Michael’s College. His work with student researchers on insect communities in the Champlain Basin is funded by Vermont EPSCoR’s Grant EPS-1101317 from the National Science Foundation.
This article was written for Northern Woodlands Magazine's Outside Story and first published on October 5 2015
The photograph of zebra mussels was downloaded from Wikimedia Commons under a CC BY-SA 3.0 Creative Commons license.
Download the Article

Thursday, December 17, 2015

Keeping it clean downstream

Agnetina.jpgIn peaceful streams, aquatic macroinvertebrates such as crayfish, stoneflies, and caddisflies travel over and under submerged rocks, foraging for other invertebrates, leaves, and algae. When rain falls, their world turns upside down.  At first only the surface is disturbed, but before long, runoff reaches the stream and increases its flow many fold. Silt and sand blast every exposed rock surface. At peak flow, boulders are propelled downstream by powerful currents.

How do small creatures survive such crushing chaos? They hunker down. Water-filled nooks and crannies extend deep below streambeds and far beyond river banks. These deep interstices provide a safe haven even while turbulent water pulverizes the riverbed, comparable to a storm cellar in a tornado.