A Flower Trap

With its foot stuck in a milkweed flower like a Chinese finger trap, the European Skipper was struggling to free itself. On another flower nearby only a leg remained from a previous struggle. Survey enough milkweed flowers and eventually you’ll find a few dead insects, usually small species, left dangling from a leg or two.

A butterfly leg left behind stuck in the flower with a pollinia attached.

They are not a carnivorous plant; trapping and death are just an accident. Instead, milkweed has solved the problem of pollination in a unique manner. There are five pinkish hoods with horns where the nectar is located. Milkweed produces copious amounts of sweet smelling nectar in the hoods to attract insect pollinators. Between each of the hoods is a dark spot with a long slit leading down from it. With most of the flowers in the umbel hanging downward, these slits are a natural place for insects to grab with their feet while syphoning nectar upside-down.

Unlike most flowers, milkweeds don’t produce tiny grains of pollen to be carried away piece by piece. Instead, the flower produces sticky, orange packets of pollen, called pollinia, which are designed to stick to an insect’s leg. In each of the five slits are two pollinia waiting to be accidentally snagged and carried off.

Butterfly leg is being pulled out with the pollinia attached.

In order for an insect to pick up one of the pollinia from a milkweed flower, its leg has to slip into a tiny slit between the anthers along the side of the flower.  As the insect struggles to pull its leg back out of that tiny opening, it might emerge with a pollinia or two stuck to it. If the insect is too small or too weak, the only way it can escape the flowers grip is to leave its leg behind. Worker bumblebees, much smaller than spring queens, that forage on milkweed often are missing a claw or leg part.

If the flower is lucky, the insect will travel to another milkweed flower in search of nectar and deliver the pollinia. To do this successfully, they must again pass their leg through one of the anther slits in another flower and have the pollinia come into contact with a very small area at the base of the stigma lobe. There’s a cost to the insect for this delivery service. Bumblebees with pollinia attached forage about 25 percent more slowly.

The odds for successful pollination are slim. Seed set in milkweeds is often quite low with only a flower or two in the entire umbel producing seed. But a few flowers are enough to produce clouds of drifting seeds each autumn to sow a new generation in some far off field.

Virginia Ctenucha (Ctenucha virginica) trapped

European Skipper resting on grass blades with milkweed pollinia stuck to several legs.

Can you spot the lost leg among the Common Milkweed flowers?

A Water Lily’s World

Water Lily Beetle (Donacia sp.)

At the height of summer many ponds are covered in lily pads with beautiful white or yellow flowers spread across the water. Moose munch on them. Beaver and muskrat devour them. Deer consider them delicious. But peer a little closer and you’ll find an amazing miniature world inhabiting each floating leaf.

In our region there are several plants with floating leaves that one may call ‘lily pads’. From bullhead pond-lily (Nuphar variegata) with its bright yellow flower petals and deep orange pistil, to the incredibly fragrant white water lily (Nymphaea odorata), or even water-shield (Brasenia schreberi) with its slimy, gelatinous-covered leaves and tiny, dark red flowers that almost escape notice; they all have specialized adaptations to allow them to rise from the deep muddy bottom up through the water column and into the air.

Water lilies are in a quandary. Their roots need oxygen, but the muck beneath the water is anaerobic. To solve this, they pump up to two liters of air from the surface down to the roots each day during the growing season using a special gas conducting tissue running down the length of stem called the aerenchyma. Air enters tiny openings on the leaf, called stomata. While land plants have them on all surfaces of the leaf, they are only found on the upper surface of water lily leaves. When the sun heats the young leaves it creates a pressure gradient that forces air down the aerenchyma. As leaves age they lose this ability to pressurize air. The roots return carbon dioxide to the surface through these older leaves.

There are many species of water lily leaf beetles that ride and feed on the surface of the lily pads. One of the earliest to emerge with the fresh leaves is named by Latin loving scientists as Galerucella nymphaeae. These oblong, dark-brown beetles are just a quarter of an inch long. They lay eggs on the surface of the leaves in June. Soon, the eggs hatch and the shiny black larvae with yellowish bellies begin to feed on the leaves. They cause the leaves to age more rapidly as they chew through them. During the height of their growth, the beetles can cause them to last just a third as long as uninhabited leaves.

Another group of water lily beetles are called Donacia. The quick moving adults have a golden metallic shine and stand tall on long legs on the lily pads. They have a layer of silky hairs on their underside that helps repel water in their soggy world. Depending on the species, some lay eggs by chewing a hole through the lily pad and then dipping their abdomen below the surface to glue rows of eggs onto the leaf. While other species may bend over the edge of the leaf to cement the eggs or climb under the leaf and down the stem to deposit eggs. Tiny grubs hatch from the eggs after about ten days and fall down through the water column eventually finding their way into the roots of the plant. The larvae have two tiny pores, called spiracles, at the end of their abdomen, each guarded by a spine. They use these as picks to open holes into the air chambers inside the plant stem thereby gaining access to a steady air supply for breathing while they feed on the plant. When ready to pupate, they build a silky, waterproof cocoon from special glands in the mouth and fill them with air by once again cutting holes into the stem’s air chambers. After developing quickly into an adult, they remain underwater until the next spring when they bursts out of the cocoon, and holding air bubbles under the wing covers and body hairs, float to the surface to find a new lily pad home.

You might notice tiny serpentine patterns snaking through the leaf surface. These are from the larvae of leaf-mining midges. Active at dusk, these tiny insects resemble mosquitoes, but don’t bite. The larvae tunnel between the leaf layers, which eventually turn brown and rot through the leaf.

Even moths find a home on water lilies. The caterpillars of the water lily borer moth feed on leaves and tunnel into the stalks of the lily pads. The poetically named polymorphic pondweed moth caterpillars feed on the leaves. As they grow larger they cut and tie two pieces of leaf tissue together and hide in it under the lily pad when they are not feeding. But perhaps the most spectacular feat is that of the water lily moth caterpillar. The adults live for just six days, but in that short time a female can lay up to 900 eggs on the surface of the lily pads. The tiny green caterpillars hatch and begin to feed on the leaves. After three weeks they’ve grown from just a few millimeters to over an inch long, turning a deep red color. Amazingly, the caterpillars swim to land using a porpoise motion with the rear third of their body. Once on land, they build a silk-lined chamber in the soil and pupate.

Flip over a lily pad and you’ll find a floating hatchery holding the eggs of mites, snails, whirligig beetles, caddisflies and others. Freshwater sponges, microscopic tube-dwelling rotifers and bryozoans colonize the surface. Snails crawl across the leaves feeding on algae. Spread across the pond each summer are entire floating worlds, each built on a lily pad.

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Note: This article first appeared in print in Rutland Magazine.

The Fresh Smell of Spring Skunk

There is nothing like the fresh smell of a spring morning, unless, during the night, a skunk skulked about your neighborhood. The striped skunk is armed with just a teaspoon of odoriferous oil in its two anal glands, but a little bit goes a long way.

When I was in junior high, I was hit with a burst of spray from a skunk at close range. I can attest that at high concentrations it causes nausea at first. It also acts like tear gas, causing watering eyes and a running nose. Oh, and your mother will most definitely make you take your clothes off outside and throw them out. If you’re lucky, she’ll let you back in after a series of home remedies, which never seem to fully cure the stench.

Skunk oil research has been going on for over a century as scientists have tried to determine what makes the stuff so potent that it can drive a bear away. Way back in 1896, Thomas Aldridge at Johns Hopkins University showed that humans could detect the smell at just 10 parts per billion, the equivalent to detecting just one drop of it diluted into a medium-sized, backyard swimming pool. More recently, William Wood, a chemist from Humboldt State University, pointed out that a number of chemicals have been incorrectly attributed to skunk oil over the years, and his work has now given us a fairly complete understanding of the chemical compounds and how to neutralize them.

The scent-gland secretion is a yellow oil composed primarily of volatile compounds known as thiols, and their derivatives. (A thiol is a compound distinguished by its sulfur-hydrogen bond.) Most of us immediately recognize the smell of ethanethiol (also called ethyl mercaptan), a common thiol that’s added to otherwise odorless propane gas so we can easily smell any leaks. Another thiol creates the “skunky” smell of beer after it has been exposed to ultraviolet light.

The thiol derivatives present in skunk oil are not particularly odoriferous, but they are easily converted to far more potent thiols when they react with water. For weeks after I was sprayed, I would give off the faint smell of skunk at basketball practice. Perhaps the thioacetate derivatives trapped in my hair reacted with the moisture from my sweat. I don’t remember, but I wonder if my defenders backed off a bit affording me more scoring opportunities. The power of thiols.

Many people believe that tomato juice will neutralize the odor of a skunk, but human olfactory fatigue is a better explanation for the apparent disappearance of the odor. I could hardly smell the odor on my body after a few hours, but when a new nose came into range, its owner squealed with disgust. A tired nose will smell the tomatoes rather than the skunk.

You can neutralize the offensive thiols in skunk spray with the sulfonic acids found in most detergents. Oxidizers such as hydrogen peroxide and baking soda are mild enough to be used on pets, although they may create interestingly colored hair for some. For washing down your deck or trash can, try liquid laundry bleach.

The smell is certainly memorable. Even decades later, the thought of that moment when the skunk turned and sprayed almost turns my stomach and brings tears to my eyes again. The skunks are reluctant to use it, though. With only enough for a half dozen sprays at most, and a 10-day period to manufacture more, skunks will only spray if they absolutely have to. In an attempt to avoid spraying, skunks often give warning. First, they show their striped white back to warn you. This is followed by threat behaviors, like stomping with both front feet, sometimes charging forward, and then edging backwards dragging their feet and hissing. If all this fails, watch out.

Each spray gland has a nipple, and skunks can aim and direct the spray using highly coordinated muscles. A skunk can spray up to 25 feet and hit something fairly accurately up to 7 feet away. When there is a target, they can direct a fine stream right at the victim’s face. When being chased, a skunk will instead emit a foul cloud for the predator to run into.

There is one predator that remains undeterred by the odiferous oil, the great-horned owl. The small size of the olfactory lobes in their brains suggests that they have a very poor sense of smell. Some individual owls can downright stink of skunk, a common complaint among wildlife rehabilitation workers. Their nests can even smell of their musky meals. But larger-lobed mammals quickly learn to avoid the white stripe in the night.

Back from the Nearly Dead

Wood Frog floating in a vernal pool.

Just a few days ago they were frozen rock hard, a frog-sicle. But today, they are barking up a storm in the pond. They’re back from the nearly dead.

Late last autumn ice began to form inside the bodies of these Wood Frogs. Glucose levels increase in their blood by as much as 200-fold in just eight hours, creating an antifreeze that preserved their tissues and organs through the long winter.

The ice penetrated throughout their abdominal cavity encasing all the internal organs. Large flat ice crystals formed between the layers of skin and muscle, and frozen lenses made their eyes white like zombie frogs. Their blood stopped flowing. As much as 65% of the frog’s total body water was locked in ice. Breathing, heart beat, and muscle movements all stopped.  The frozen frogs were in a virtual state of suspended animation. They were nearly-dead.

Female Wood Frog has just emerged from underground for spring migration to a nearby pond.

When melting snow and spring rains began to seep into the ground, the Wood Frogs became aroused from their frozen state and began their annual migration to breeding pools. Remarkably adapted to the cold, it is not unusual to find individuals scampering across old snow or swimming in water amidst ice.

Wood Frogs are explosive breeders, and most mating in a given pool takes place over just a few days. The loud duck-like calls of males are often a key to finding these pools. Females often deposit their gelatinous egg masses communally. The center of an egg mass may be up to 5°F warmer than the surrounding water, speeding development. Eggs often become covered by symbiotic algae (Oophilia ambystomatis) that enhance the oxygen supply to developing embryos in exchange for nutrients and carbon dioxide.

By mid- to late-summer nearly all juvenile frogs have left the pool as it dries up. Over 70% of these will succumb to predation before reaching adulthood. The rest will be frozen in time until spring comes again.

From a Peep to a Cacophony

Spring PeeperIt’s a warm evening, and the only signs of snow are the eroding piles beside the driveway. Down in the valley, there is a chorus erupting, and up on the hill in a pond, another is just beginning. The spring peepers are in stereo. Spring has finally sprung.

The cacophony is emanating from hundreds of male spring peepers. Each peep is made when a frog forces air from its lungs, over the vocal cords in the larynx, and into an air sac in its throat. The air enters the sac from openings on each side of the mouth cavity, causing the sac to balloon outward. The inflated sac acts as a sounding board, amplifying the sound and carrying it from the frog to my ears across the valley.

What sounds like chaos to me sounds organized to a peeper. Several males may interact vocally by forming duets, trios, or quartets, with alternating peep calls and individual notes. When males alternate calls, one individual, the follower, usually calls within 40 to 70 milliseconds from the end of the leader’s call.

Males tend to stay within a close pitch range of each other. The spacing and timing of calls accentuates the distinctiveness of each male’s call so that it is not lost in the overall din and allows a female to zero in on a single calling male. When another male frog moves too close, one male may use a second type of call, a trill. The trill seems to reflect a higher degree of aggression than the peep call and will stimulate one of the individuals either to move away or perhaps to trill back in challenge, causing a trill-off. A trill-off can escalate into a brief physical scuffle, with the winner staying and the loser moving on to quieter waters.

Each male peeper can pump out from 3,000 to 4,000 peeps an hour for several hours each night. So it is not surprising that male trunk muscles, which help propel air from the lungs, average 15 percent of their body mass compared to only 3 percent for the quiet females. Aerobic capacity of trunk muscle is six times that of leg muscles and, in males, is 17 times greater than that of female trunk muscle. Peepers derive about 90 percent of their energy for call production from fat reserves in these muscles. Males weigh on average about the same as two dimes, yet their sound pressure is comparable to the song of a warbler (about 4 quarters in weight) or a blackbird (a whopping eight half-dollars in weight). These little peepers have big bellows.

The peeper mating system is based on female choice. The louder and faster he peeps, the better his chances of attracting a receptive female. When biologists played recorded peep calls for female peepers, the females preferred peep rates double those found in the wild, indicating a strong sexual selection for males that can peep fast. Male peepers, therefore, push their singing abilities to the limit, performing at or close to their full physiological capacity. But one night of binge calling doesn’t seem to wear them out: males that have the higher peep rates in one night tend to have higher peep rates every night.

The evening temperature can affect calling patterns. On warmer evenings, peepers call much more frequently. The consumption of oxygen increases with calling rate, which in turn increases with temperature. At a balmy 60°F, peep calls are repeated up to 13,500 times per night.

Not all males sing, though. A big chorus of singers will also attract a host of silent males, who mix in around the edges. These shy guys tend to be smaller than the big singers. They quietly wait near a good singer, watching for a female that may be attracted to a peeping male. When she comes along, they use their quickness and agility to beat the singer to the female.

According to the Vermont Amphibian and Reptile Atlas, peepers can begin calling as early as March 15, with peak activity in early May. Chances are good that the spring peeper chorus is now happening earlier than in the past, according to a study by James Gibbs, from the State University of New York in Syracuse, and Alvin Breisch, of the New York Department of Environment Conservation.

From 1900 to 1912, Albert Wright, an instructor in zoology at Cornell University, visited ponds around the campus daily each spring to record the date of the first calls of frogs. Ninety years later, volunteers collected the same kind of information for the New York Amphibian and Reptile Atlas, allowing Gibbs and Breisch a chance to compare. Wright, on average, heard his first peepers on April 4. Atlas volunteers heard them around March 20, about 13 days earlier.

For us, it is spring music to our ears. For the peepers, it is a singing battle of life and death. I hope their spring tradition goes on and on.

Hidden in Underwear

Western Conifer Seed Bug (Leptoglossus occidentalis)

There was a scream upstairs and then a yell for mom. It sounded like another teenage moment so I kept my nose in my book downstairs. A few minutes later my wife showed up at the table with a pair of underwear in her hands. “Can you tell me what this is,” she asked. I thought about telling her it was indeed a pair of dirty underwear, but her white knuckled grasp of it was an indication that this was no time to be smart-alecky. She loosened her grip a bit and there in her hand was what appeared to be a Hemiptera. The odor it was emitting was quite pungent when I grabbed it and put it to my nose. Now I was really interested.

What my girls had found crawling on the wall was a Western Conifer Seed Bug (Leptoglossus occidentalis). This bug was originally a Pacific Northwest species, but it has been moving eastward for the last 100 years. Our winter guest is in the family of squash bugs or leaf-footed bugs, named for the leaf-like flattened extensions on their hind legs. Nationwide, there are 88 species of leaf-footed bugs. All of them feed on plants. Our little friend enjoys the sap from developing pinecones.

It was very tame and easily handled. They are not poisonous and they don’t cause any damage. They’re just trying to get out of the cold. Normally, they winter under tree bark or crevice near the evergreens they feed on. There is a Red Pine tree right beside our house, so it wandered in somehow.

That scent I smelled? It was an alarm pheromone that is secreted from glands and consists mostly of hexyl acetate, which is often used in the creation of fragrances and flavor manufacturing, as well as hexanal, which is used to make fruity flavors in foods.

This bug was a lucky one. I put him outside on the pine tree and far away from the underpants monster.