A Field Guide to July 2017

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A summer hike in the Green Mountains of Vermont. / © K.P. McFarland

The avian breeding season is winding down. Even a few southbound shorebirds will trickle through the region this month on their “fall” migration. But as the dawn bird chorus now fades from northern woodlands, fields and wetlands erupt in the sparkle and drama of summer insects. Here’s a short guide to some of July’s lesser known natural history.

NATIONAL MOTH WEEK – July 22nd to 30th

Moth watching on a warm night. The black light is an old ‘bug zapper’ that has had the zapping parts removed.

National Moth Week celebrates the beauty, life cycles, and habitats of moths. “Moth-ers” of all ages and abilities are encouraged to learn about, observe, and document moths in their backyards, parks, and neighborhoods. Held worldwide during the last full week of July, National Moth Week offers everyone, everywhere a unique opportunity to become a citizen scientist and contribute information about moths. Through partnerships with major online biological data depositories, participants can help map moth distribution and provide needed information on other life history aspects around the globe. Here at VCE, we map moth distribution throughout the year on iNaturalist Vermont, a project of the Vermont Atlas of Life.

How many moth species can we find during moth week?

We encourage you to add your photographs of moths too. Moth watchers have added a whopping 91 news species to the Vermont checklist via iNaturalist Vermont and have documented 864 species across the state. What’s even more amazing is that we’ve recorded over 15,000 moth observations, which help to understand their phenology, habitat use and range in Vermont like never before.

I Tasted a Moth Last night and it was terrible

Seriously, don’t do this at home. I tasted a frothy moth secretion last night and it was downright awful. I should have known from the smell alone, which I can only describe as a strong, old attic odor. But I’ve heard for years that these tiger moths were wildly and brightly marked to warn predators of their awful taste, so I had to try it myself. And it’s true. You’re going to want to read the whole story on our blog…

An arms race

Big Brown Bat digesting an evening meal. / © K.P. McFarland

By Kent McFarland

For nearly 65 million years bats and moths have been locked in an evolutionary battle of predator verses prey. Bats generate ultrasonic sounds that bounce off objects before them. The returning echoes allow bats to create a three-dimensional map in their mind’s eye with amazing acuity, including the moths flying across the night sky. But moths have countered this nighttime vision with their own extraordinary adaptations.

Depending on what family they belong to, moths have a diverse array of hearing devices. Some have head appendages while others have more ear-like vibration receptors called tympani on each side of their body. The tympanum is an extremely thin cuticle that is very responsive to vibrations. When sound waves hit the tympanum making it vibrate, tiny sensory cells capture the mechanical vibrations and turn them into nerve impulses. Each ear is equipped with just a few sensory cells, while our ears have over 15,000 receptor cells. While we need to hear the nuances of speech, moths need one message – is a bat about to make it a meal?

Many owlet moths, a diverse family with over 500 species found in Vermont alone, can hear the high-frequency echolocation calls of bats. They can detect the sounds of a Big Brown Bat, a common species in Vermont, when it is nearly 100 feet away. When a moth hears weaker calls, indicating the bat may be some distance away, they tend to flee from the detection. But a strong detection of an approaching bat call instantly and involuntarily causes the moth to fly erratically. The moth’s wing muscles literally go into spasms causing their flight to be an unpredictable loop, twist or twirl. A last ditch effort by the moth to avoid capture is to completely fold its wings causing a free-fall. The moths respond to approaching bat calls in a mere 40 to 100 milliseconds, about the time one or two frames in a video flash on a screen. Be quick or be eaten.

Tiger moths, a diverse subfamily with over 11,000 species worldwide, have even more elaborate defense systems. Tiger moths that fly by day are more likely to use bright coloration to warn of their distastefulness to predators such as birds. The toxic chemicals in the plants that the caterpillars eat remain and protect them into adulthood. While tiger moths that fly mostly at night rely more on sound to ward-off echolocating bats.

Virgin Tiger Moth (Grammia virgo). / © K.P. McFarland

The Virgin Tiger Moth that haunts forest edges throughout the Northeast in late summer has it all – bright colors warning of their distasteful poisons during the day and acute ears and high-frequency click sounds give warning at night. When the moth hears a bat coming near, the tymbani begin to snap. They work like the popper in the board game Trouble. Push it down and it snaps back with a clicking noise. And if all those defenses fail, when an adult is handled it oozes a yellow, frothy foam from the back of its head that contains smelly and distasteful alkaloids that it consumed as a caterpillar.

A tiger moth that inhabits the Southwest has actually developed the ability to jam a bat’s echolocations with its sound. Biologists have measured up to 450 clicks in just 1/10th of a second from its tympanum. When a bat is about to lock onto its target, it emits a rapid series of echolocation calls that are nicknamed the feeding buzz. But at the same time, the moth begins to rapidly click its tympani. The interference confuses the bat, slowing it down, and often causing it to miss its target.

Closer to home, the elegant Luna Moth has developed another defensive trick. They’re one of four species of giant silkmoths in Vermont, and as the name suggests, they’re huge – as big as your hand. The Luna Moth is perhaps one of the most visually arresting and popularized moths with its lime green wings edged in pink or yellow, eyespot starring back, and its long twisted tails fluttering through the night.

Jesse Barber from Boise State University and his colleagues have recently shown that the Luna Moth’s tails are not decorative, they’re distractive. They pitted Luna Moth against Big Brown Bats and spied on the outcome using high-speed infrared video cameras. The bats were able to grab just 35 percent of the moths. But if they removed the moth’s tails, which didn’t affect the flight of the moths, the bats caught over 80 percent of them.

The Luna Moth’s tails spin as they fly, reflecting the bats sonar. To the bat, the tail appears as a bull’s eye or a confusing second target. Either way, they bat strikes out or at best grabs a tail leaving the rest of the moth intact. The benefit of having a tail was roughly equivalent to the advantage other moths have from bat-detecting ears.

For the last decade the night skies may have been safer for moths. White-nosed syndrome, an introduced fungus that attacks some bats that hibernate in caves, has killed millions of them in eastern North America since 2006. Moths may now be getting a more predator free flight.

The disease has decimated two of Vermont’s formerly most common species, the Little Brown Bat and the Northern Long Eared Bat. Their populations have declined by about 90%. But moths still need to keep their guard up. Big Brown Bat and some woodland bat species are still relatively common. The skies may be a bit quieter for moths, but danger still echoes in the night sky.

It smells like a skunk

A pungent Skunk Currant growing along a hiking trail on Mount Mansfield, Vermont. / © Jason Hill

By Jason Hill

Despite the name, Skunk Currant (Ribes glandulosum) produces a tasty berry…if you can get past the pungent smell that develops as the fruit ripens. This low-lying shrub of the subalpine and alpine zones prefers moist soils, and produces a small, white five-petaled flower with purple stamens in May. The Skunk Currant’s specific epithet stems from the stiff glandular hairs that cover the ripening fruit in July and August. The leaves often take on a stunning assortment of red coloring in the fall.

However, Ribes species (currants and gooseberries) are carriers of white pine blister rust, which can lead to localized loss of high-elevation White Pine (Pinus strobus) in New England. This rust is caused by a fungus (Cronartium ribicola), native to Asia, which has a complex life cycle requiring multiple hosts. All North American white pines are susceptible. Ribes spp. that carry this rust develop tiny yellow spots and orange-yellow fruiting bodies (that resemble metal rust) on the leaves. Ultimately these fruiting bodies (uredia) produce wind-transported uredospores that can infect White Pines within several miles. Infected pines develop cankers that destroy the cambium, thus reducing the pine’s ability to transport water and nutrients. Infected pines often have browning needles, top dieback, and trunk lesions that produce abundant amounts of resin.

Check out all the observations of Skunk Currant on iNaturalist Vermont, more images and a phenology chart, and add your observations too.

A nest full of mushrooms

By Kent McFarland

Crawling on my hands and knees through the thick, stunted forest near treeline, a subalpine forest formation called krummholz, I stumbled upon some fine, black hairs wrapped around a dead Balsam Fir branch just above the mossy understory. I immediately recognized them.  I had seen them woven into the lining of songbird nests I was studying. And remarkably at the very end of a few of these hairs was a tiny mushroom cap not much larger than the head of a pushpin.

Bicknell’s Thrush nestlings / © K.P. McFarland

George Wallace, born and raised in Vermont and later a great ornithologist, studied the life-history of Bicknell’s Thrush in the 1930s on Mount Mansfield, Vermont, not far from where I found these mushrooms. Wallace described in great detail the nests he had found, but he was unable to identify the inner lining of “fine, black rootlets” and commented that “they are unquestionably rootlets of some sort… resembling horsehair, but where the birds get them is a mystery.” I had a hunch I had solved that mystery.

I collected a sample as I lay hunched under the crooked trees. Later, when the birds were done breeding, I collected a few of the nests. Nearly all of them had copious amounts of the black, rootlet lining, which was a perfect match for my sample. But not one appeared to have a mushroom cap. I found the tiny mushrooms in the forest after a rainy period. Perhaps they needed moisture. I placed one of the nests in a plastic container with just a bit of water sprinkled on the bottom. Within just a few days some of the rootlets appeared to spring upward with caps on them. But what kind of mushroom grows in such a strange manner?

Samples of the hair-like structures and caps were sent to a North American expert, Dr. Dennis Desjardin, Director of H. D. Thiers Herbarium at San Francisco State University, for identification. The hair-like structures were identified as rhizomorphs of the Horsehair Fungus (Marasmius androsaceus). It’s considered common in North America, and can be found across the boreal zone and south along the Rockies, the Coastal Mountains and the Appalachians. It belongs to a group of closely related species, all of which produce numerous rhizomorphs.

The thread-like rhizomorphs are made up of parallel hyphae, branched tubular filaments that make up the body of a typical fungus, and absorb and transfer nutrients. Horsehair Fungus is saprotrophic, an organism that lives and feeds on dead organic material, and is found on dead needles, leaves and twigs and parasitic on some ericaceous plants in wet, boggy habitats. They penetrate solid materials such as dead wood and use acids and enzymes to digest it.

The use of rhizomorphs as nesting material, especially by tropical bird species, has been found to be widespread but poorly documented. It had not been reported for any birds breeding in North America prior to my discovery. From Bicknell’s Thrush to Yellow-bellied Flycatchers, we’ve found that most subalpine songbirds in the Northeast use these mushrooms in nest construction, but why?

A number of Marasmius species have been shown to produce antibiotic agents that inhibit the growth of Staphylococcus. However, Marasmius androsaceus, was practically inactive upon Staphylococcus cultures when tested years ago. While it is possible that this fungus may be an effective agent against nest pathogens and parasites of subalpine birds in the Northeast, this is not known. Bernd Freymann from the University of Groningen in the Netherlands examined the physical properties of Marasmius rhizomorphs used by Streak-backed Orioles in nests in Central America. The rhizomorphs had significantly higher tensile strength and absorbed less water than alternative available fibers in the area.  Alternatively, they may simply provide the best of most easily obtainable material in the subalpine forest for lining nests.

Whether the birds are shaman selecting a fungus for medicinal properties, engineers selecting the best construction materials, or just grabbing what is handy; I marvel at the intricate relationships of nature all woven in the lining of a nest.

It’s Not Just a Ride, It’s Phoresy!

Water Mite (Arrenurus) larvae on a Dragonfly. / © K.P. McFarland

By Kent McFarland

I really don’t like weeding. So it was with great pleasure when just moments into the task I spotted a dragonfly on one of the nearby plants acting strangely. What immediately caught my eye was a pile of tiny, red, egg-like sacs all over its thorax. I ran to grab my camera, and at this point, I am sure my wife was rolling her eyes. Anything to get out of weeding. But heck, I was just about to bear witness to phoresy.

Frankly, I didn’t know the term either. But it turns out that those little red sacs weren’t eggs at all, but rather larvae of water mites and they were hitching a ride on the dragonfly. Ecologist call it phoresy, the process of using another organism to move about.

Arrenurus water mite adults are a mere three millimeters long and usually brown or greenish so you wouldn’t really notice them in the water unless you were really looking for them. They mate in the spring and the female lays up to 400 red eggs on underwater objects, one egg at a time.

The six-legged larvae hatch in one to six weeks, depending on water temperature, and they immediately swim around looking for an insect larva. When they find a mosquito, stonefly, damselfly or a dragonfly larva that is in its late stages of growth, they grab onto it, waiting until the larva goes airborne.

As the dragonfly larva crawls out of the water and sheds its exoskeleton, the mites jump off the cast shell and onto the dragonfly. Now they are not only hitchhiking, but they also become parasites. They form a tube that pierces the exoskeleton of the dragonfly so that they can feed on the victim’s hemolymph, kind of like blood in an insect’s circulatory system. After the mite grows enough, its exoskeleton becomes like a sac and inside the larva develops into a nymph.

When the nymph is fully developed, it just drops off the host when it is over water. Now, like all arachnids, it has eight legs and looks similar to an adult water mite. They eat the same foods as adults too – tiny insects, worms and even other mites. After they eat and grow, if they avoid being eaten themselves, they find an object to attach to and form another sac to develop into an adult.

It’s a complicated life cycle for the minute water mite. I never would have guessed that they visited our nicely weeded garden far from water

More July Wonders

Confusing Bumble Bee (Bombus perplexus) nectaring Common Milkweed. / © K.P. McFarland

There’s even more July sparkle to read about in our 2016 issue. Check it out and learn about milkweed pollination, primrose’s ruse, life and death on a lily pad, and big and showy darner dragonflies. Most importantly, get outside and discover the biodiversity unfolding around us and if you’re in Vermont, share it with us on iNaturalist Vermont.

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Comments (1)

  1. jerryspass says:

    Nice photos Kent.

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