As the dawn bird chorus now fades from northern forests, summer erupts in the sparkle and drama of insects. Here’s a short guide to some of July’s lesser known natural history.
Four plants serve as a backdrop for four natural history events not to be missed here in the Northeast each July. So consider this your annual reminder to seek out drama among the plants.
Although it is by no means a carnivorous plant, Common Milkweed can be a killing field for small insects. Take the saga of this Virginia Ctenucha moth. With two legs stuck in milkweed flowers like a Chinese finger trap, the moth was struggling to free itself. On another flower nearby only a leg remained from an insect’s 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. What’s going on here? Here’s a full report from a field full of milkweed.
Like most of you, Bryan Pfeiffer likes to spend his summer leisure time contemplating the tongue of the Primrose Moth. Okay, it’s not exactly a tongue. Butterflies and moths have a straw-like proboscis that they coil like a watch spring and unfurl to suck nectar from flowers (and essential minerals from mud or scat). The Primrose Moth’s proboscis is about half the length of its body. That anatomy alone might be enough to generate interest in this insect. But now consider that the Primrose Moth is Pepto-Bismol pink with a lemony margin at the tips of its wings. In that pink presentation and probing proboscis, the Primrose Moth offers us a lesson in form, function, and evolution. Read more on Bryan’s blog.
At the height of summer many ponds are covered in lily pads with beautiful white or yellow flowers spread across the surface. 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. Even moths find a home on water lilies. The caterpillars of the Waterlily Borer Moth (Elophila gyralis) feed on leaves and tunnel into the stalks of the lily pads. Here’s a report knee deep in a pond.
A Ruby-throated Hummingbird can extend and retract its tongue about 13 times a second. Jewelweed, with its bright orange flowers, attracts hummingbirds and takes advantage of their particularly speedy eating habits to dust the bird with pollen. A single hummingbird can visit as many as 200 flowers in 15 minutes, but can only collect a small amount of nectar – the equivalent of about a few grains of sugar – from each flower.
Ethan Temeles and his students at Amherst College discovered that the jewelweed flower is specially adapted for the feeding style of the hummingbird. The only thing you might notice while watching one of Ethan’s videos of a hummingbird feeding at a jewelweed flower is that the flower shakes back and forth while the bird’s bill probes into the flower. This doesn’t seem like anything remarkable, but to the biologists it was a clue.
Apparently, the flower movement is an adaptation to better smear pollen on the unsuspecting hummingbird. The jewelweed flower has a tiny opening that is about four millimeters wide at the entrance and quickly narrows to only one millimeter wide, bending sharply down and back again toward the front of the flower. At the end of this circuitous tube is the liquid prize for the hummingbird: sweet nectar.
The bird hovers in front of each blossom, using its long tongue to reach down into the flower tube. When the tongue gets to the sharp turn in the tube, it pushes the flower away, then continues on to the end of the tube, where nectar flows into channels on the tongue. The bird then pulls its tongue back to drink the nectar, thus releasing pressure on the back of the tube.
Each jewelweed flower hangs from a stem with just enough tension to allow it to spring back and forth as the hummingbird feeds, depositing pollen on top of the bird’s bill and forehead. When the hummingbird visits another flower, the pollen it carries is brushed off, thus fertilizing a new flower.
Monarchs are famous for their amazing fall migration, flying thousands of miles from the northern U.S. and Canada south to winter in the mountains in central Mexico each year. The last generation of monarchs, those that will ultimately migrate, are produced in July – perhaps in a milkweed patch near you.
Arriving as early as mid-May in some years in the Northeast, monarchs probably have two generations here during the summer before migrating southward each fall. Some years, its impossible to find caterpillars of the second generation in July and August, while in other years (last year was above average), they seem to be plentiful. I have noticed that in late July and August, the place to find hungry caterpillars is on younger and more succulent milkweed. And in late summer, the only places you find this are areas that were mowed in early July.
Research in New York found that manipulating Common Milkweed phenology through mowing could be used to increase monarch productivity in late July and August. Biologists mowed strips in fields at the beginning of July, late July, and mid-August. They compared these to unmowed control areas by carefully monitoring milkweed growth and counting monarch eggs and caterpillars. As they predicted, mowing fields with Common Milkweed extended the monarchs’ breeding season and increased overall monarch reproduction.
The authors wrote, “We found mowing on July 1 and 24 spurred the regrowth of milkweed and sustained a more continuously suitable habitat for monarch oviposition and larval development than the control. Mowing on August 17 proved too late for recovery of the milkweeds. Significantly more eggs were laid on the fresh resprouted milkweeds than on the older and taller control plants. In the strips mowed on July 1, peak egg densities occurred in late July; in the strips mowed in late July, peak egg densities occurred in early to mid August.” But it is important to remember that if you mow for monarchs, only mow patches or some strips so that older growth and other flowering plants will be available for adults and other pollinators.
Adult monarchs need sources of nectar to nourish them throughout the entire growing season and during migration. Try to include a variety of native flowering species with different bloom times to provide monarchs with the food they need to reproduce in the spring and summer and to migrate in the fall. Offering a wide array of native nectar plants will attract not only monarchs but other butterflies and pollinators to your habitat all season long. You can get a list of monarch nectar plants for your region from Xerces Society’s Monarch Nectar Guides.
In the last two decades, the eastern monarch population has declined by 80%. We still have a lot to learn about monarchs in order to protect them efficiently, and you can help! From July 28 to August 5, butterfly watchers across North America are invited to take part in the International Monarch Monitoring Blitz to help provide a valuable snapshot of monarch population status across their late summer range. Participation is simple: find a milkweed patch and look for monarchs, counting the number of stems you examined as well as the number of eggs, caterpillars, pupae, and adults. Then, share your observations with Mission Monarch. Visit Mission Monarch to learn more.
Seriously, don’t do this at home. I tasted a frothy moth secretion one 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.
I was mothing on the back deck when a gorgeous Virgin Tiger Moth (Grammia virgo) fluttered onto my white sheet. I snapped a few shots of it and then I decided to move it to a nearby plant for a more natural looking image. I gently shifted it off the sheet and onto my hand and walked a few feet over to my pollinator garden. Almost immediately, a yellow, frothy goo began to ooze from the front corner of the moth’s thorax (the “shoulder” area).
It’s been long known that these moths have a nasty chemistry. In 1859, Thaddeus William Harris wrote in A Treatise on Some of the Insects of New England: Which are Injurious to Vegetation that, “The largest and most rare of these moths is the Arctia virgo, or virgin tiger moth. On account of the peculiarly strong and disagreeable odor it gives out, it might, with greater propriety, have been named the stinking tiger moth.” The same year in The Life of North American Insects, Jaeger and Preston wrote, “The Virgin Tiger Moth is one of the handsomest and largest of this genus, but on account of its fetid odor it is very disagreeable to handle.” And more recently in 2005, David Wagner wrote in his amazing book, Caterpillars of Eastern North America, that when “adults, when gently squeezed, may bubble generous amounts of their yellow “blood” out of the front corners of the thorax, yielding a frothy mass that contains alkaloids that the caterpillar has consumed.”
I dabbed a bit of the viscous material from the moth onto my forefinger and placed it on my tongue. Wagner’s note of alkaloids explains the intensely bitter taste I experienced. I immediately went inside to rinse my mouth.
For nearly 65 million years moths have been locked in battle with their predators. Bats developed ultrasonic sound to track moth prey at night. Moths countered with ears capable of hearing the bats. The bats responded by changing their frequencies. Tiger moths responded with the ability to actually create their own ultrasonic sound. They are locked in a coevolutionary predator versus prey race for survival.
Many moths in the Noctuidae family have tiny organs in their ears that can hear bat echolocation calls. These moths respond to the detection of bat calls in a mere 40 to 100 milliseconds. Be quick or be eaten. Weak calls, indicating a bat may be some distance away, causes the moth to flee from detection. The strong call of an approaching bat instantly produces erratic flight; the moth’s wing muscles literally go into spasms, causing their flight to be unpredictable loops, twists, or twirls. A last-ditch effort to escape a pursuing bat is the complete folding of wings and ensuing free-fall. Diurnal tiger moths (active during the day) are more likely to use visual avoidance signals, such as bright coloration to warn of their distastefulness to predators like birds. Those that fly mostly at night rely more on sound to ward off echolocating bats. The Virgin Tiger Moth that haunts my backyard has it all – bright color, bad taste, and cloaking clicks in the night.
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 the Vermont Atlas of Life on iNaturalist, a project of the Vermont Atlas of Life.
We encourage you to add your photographs of moths, too. Thanks to the tireless efforts of both professional and amateur Lepidopterists since the 1995 landmark publication Moths and Butterflies of Vermont: A Faunal Checklist, nearly 400 new moth species have been found in Vermont. Preliminary results show that there are now over 2,200 species of moths known from Vermont. And, there are likely many more awaiting our discovery.
Since 2013, professional biologists and naturalists have contributed moth observations to the Vermont Atlas of Life on iNaturalist. Many of us turn on special lights in our backyards on summer nights to find hundreds of moths and other insects gathering on our sheets, hunt fields and forest for day-flying moths, and place rotten fruit bait out to attract other moths. Many of these moths can be identified from good photographs (although some are impossible without dissection and examination under a microscope). With today’s amazing digital photography technology, coupled with the newer Peterson’s Field Guide to Northeastern Moths and web sites like iNaturalist Vermont, BugGuide, Moth Photographers Group, or Moths of Eastern North America Facebook Group, moth watching (aka mothing) has become increasingly popular.
Moth watchers here in Vermont have added nearly 100 new species to the Vermont checklist via the Vermont Atlas of Life on iNaturalist and have documented nearly 1,400 species across the state so far via iNaturalist. What’s even more amazing is that we’ve recorded over 40,000 observations, which helps us understand their phenology, habitat use, and range in Vermont like never before.
I really don’t like weeding. So it was with great pleasure when just moments into the task I spotted a dragonfly acting strangely on a nearby plant. 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 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 notice them in the water unless you were really looking for them. They mate in 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
Bumblebees do it. So do carpenter bees. They sometimes cheat and rob flowers blind. Faced with a short tongue and a long flower, some bees make a cut at the base of the corolla with their strong mandibles and sip the nectar within. But it’s the flower’s loss. The bee bypasses the end of the flower where the anthers are full of pollen waiting for transport and the stigma waits for a pollen delivery. The plant gives up its sugary treat with nothing in return. Once there is an access hole, other insects will take advantage of the easy access too. Watch the long flowers in your garden and see if you can witness a robbery!