Month: November 2024

 

 

The past couple of weeks we have explored the strategies insects use to deal with chilly winter weather in temperate parts of the country, including the DMV. We learned that some butterflies and true bugs (Hemiptera) employ a snow-bird strategy and simply migrate south to warmer regions to avoid freezing to death. But not everyone gets out of town. Last week we met the banded woolly bear caterpillar and its cousin the giant woolly bear. Think about the lowly banded woolly bear caterpillar. How long would it take for these caterpillars to wiggle their way from the DMV to Florida to avoid freezing to death? That doesn’t happen. So, what do they do? Through eons of trial and error, woolly bear caterpillars and several other species of insects have evolved a strategy called freeze tolerance. Here’s the backstory.

Insects and many other animals like reptiles and amphibians are ectotherms. Unlike humans, other mammals, and birds whose temperatures stay more or less constant, ectotherms rely primarily on ambient temperatures to heat or cool their bodies. Most insects that winter-in-place where freezing temperatures prevail enter a state of dramatically reduced development called diapause. Diapause is triggered by environmental cues such as changing food availability and quality, changing day length, and cooling temperatures. These cues initiate physiological processes to acclimate in preparation to endure winter’s cold. When temperatures drop below freezing, water molecules inside cells throughout the insect’s body can form lethal ice crystals that can destroy cells and result in a chilly death. The lowest temperature an animal reaches before freezing is called the super cooling point (SCP).

Some Freeze tolerant insects produce compounds called ice-nucleating agents. These agents cause ice crystals to form rapidly and harmlessly in the hemolymph at relatively high temperatures. Water molecules move from within cells to the hemolymph where they also freeze. This prevents ice crystals from forming inside cells where they could rupture cells and cause cell death. Insects like bald-faced hornets employ this clever tactic. A second group of compounds called cryoprotectants have been discovered in several freeze tolerant insects like our friend the banded woolly bear, as well as the spring field cricket. These compounds include sugar alcohols such as glycerol, sorbitol, and trehalose, and amino acids like proline. Cryoprotectants act in the same way as ethylene glycol in the radiator of your car, which prevents your engine coolant from freezing. Cryoprotectants prevent ice formation, keeping vital fluids liquid and thereby allowing the supercooling point of an insect to drop dramatically.

Insects living in regions where winter temperatures dip below freezing evolved clever ways to avoid a chilly death. Some species like overwintering baldfaced hornet queens produce compounds that hasten the formation of ice crystals in their blood. This prevents ice crystals from forming inside cells where they would lethally rupture cells and kill the queen. Another freeze-tolerant insect, the spring field cricket, is close kin to the fall field cricket we visited in a previous episode.  Banded woolly bears that we met last week don’t employ ice-enhancing compounds. Instead, they produce antifreeze-like compounds, cryoprotectants including glycerol and sorbitol. These protectants prevent their cells and blood from freezing at subfreezing temperatures that are normally encountered in their habitats. This allows woolly bears to chill-out rather than die.

Of course, for all insects there will be a minimum temperature at which life will be impossible. This varies both within and between insect species and depends on a variety of environmental conditions leading up to and during the seasons of subfreezing weather. So, how low can freeze tolerant insects go before they freeze to death? One tiny fly that makes galls on goldenrod in North America can survive temperatures of -40 degrees Fahrenheit or less. Now that’s one cool fly!

Acknowledgements

The following articles provided fascinating insights into the overwintering and anti-freezing strategies of insects: “Insect antifreezes and ice-nucleating agents” by John G. Duman, “Cold Hardiness of Insects and the Impact of Fluctuating Temperatures” by Ashley Dean and Erin Hodgson, “Freeze tolerance and cryoprotection in caterpillars of the giant leopard moth (Ecpantheria scribonia Lepidoptera: Arctiidae)” by Jack R. Layne Jr., “How crickets become freeze tolerant: The transcriptomic underpinnings of acclimation in Gryllus veletis” by Jantina Toxopeus, Lauren E. Des Marteaux, and Brent J. Sinclair, “The sub-lethal effects of repeated freezing in the woolly bear caterpillar Pyrrharctia Isabella” by Katie E. Marshall and Brent J. Sinclair, “Cold-hardening of the ground beetle Carabus granulatus L. (Coleoptera:Carabidae)” by Irja Kivimägi,  Angela Ploomi, Anne Luik, Katrin Jõgar, Ivar Sibul, and Aare Kuusik, “Landscape effects on the thermotolerance of carabid beetles and the role of behavioral thermoregulation” by Lucy Alford, Sacha Roudine, Jean-Sébastien Pierre, Françoise Burel, and Joan van Baaren, “The role of ice nucleators in the frost tolerance of overwintering queens of bald faced hornet” by J. G. Duman and J. L. Patterson, “Changes in Chemical Composition and Accumulation of Cryoprotectants as the Adaptation of Anholocyclic Aphid Cinara tujafilina to Overwintering” by Roma Durak, Joanna Depciuch, Ireneusz Kapusta, Joanna Kisała, and Tomasz Durak, “Cold Hardiness of the Woolly Bear Caterpillar (Pyrrharctia isabella Lepidoptera: Arctiidae)” by Jack R. Layne Jr, Christine L. Edgar, and Rebecca E. Medwith, and “Insect overwintering in a changing climate” by J. S. Bale and S. A. L. Hayward.

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Mice are curious, agile, adaptable critters that run rampant across the globe. Two of the most common mice found throughout the Northeastern United States are deer mice, which is a type of field mouse, and house mice. Understanding the difference between the two and learning how to accurately identify these pests can aid in minimizing health risks. It’s also the key to unlocking effective mouse elimination strategies.  

Introduction to Deer Mice and House Mice 

What is the difference between deer mice and house mice? These two species are among the most common mice found throughout the Northeastern United States. Although they are both tiny in size, these creatures can create big problems when they decide to move into your home or other structures.  

Why It’s Important to Differentiate Between Deer Mice and House Mice 

Deer mice and house mice pose separate risks, with house mice closely linked to secondary pests like fleas and dangerous pathogens like salmonella. On the other hand, deer mice can carry Lyme disease and transmit other illnesses, including Hantavirus, which can spread by inhaling germs from deer mouse droppings or urine.

Perhaps even more importantly, knowing which type of mouse you are dealing with will guide your treatment and removal strategy.  

Overview of the Most Common Types of Mice Found in Homes 

Tons of different species scamper about around the world, but only three are typically found in this region: deer mice, house mice, and white-footed mice. White-footed mice are closely related to field mice and can be identified by the color of their feet. Deer mice and house mice are two of the most likely culprits for infestations. 

Key Differences in Appearance 

To those who are unfamiliar with these pests, mice can look pretty similar. However, when you know what to look for, the subtle differences are easier to spot and can help you figure out exactly what kind of mouse has become an uninvited houseguest.

Physical Characteristics of House Mice 

As a general rule, field mice have white bellies with either gray or brown backs. House mice are dark colored and fairly solid or slightly lighter bellies with a nearly hairless tail. 

Physical Characteristics of Deer Mice 

Unlike house mice, deer mice have hair on their tails and brown or dark brown fur on most of their bodies, except their white-furred bellies. These mice have larger eyes and rounder ears and typically grow up to seven inches long, including their two-toned tails.  

How to Identify Mice Based on Appearance 

• Eyes and Ears: Are they small and beady or larger and rounder?
• Fur Color: Is the fur primarily a single color or two-toned? 
• Tails: Is the tail as long as the mouse and hairy or shorter, two-toned, and hairless? 

Behavioral Differences Between Deer Mice and House Mice 

Inside homes, field mice (deer mice and white-footed mice) are most commonly found in the basements, attics, and inside walls. House mice, however, are most commonly found in kitchens, pantries, and the living space (especially around the perimeters of the room). Other differences between these common household nuisances include the following:  

Habitat Preferences 

Although all mice love fields and forests, house mice are equally comfortable in urban environments. Deer mice, on the other hand, prefer parks and meadows, making them more likely to infest cabins and homes in quieter, rural settings.  

Nesting and Feeding Behaviors 

as a general rule regarding mice inside of a home, field mice (deer and white-footed) get their food from the fields and house mice get their food from the house. Field mice will often leave the structure to gather seeds and nuts or other food outdoors and bring it into the home to store it, eat it, and use the house as a shelter and a place to have their babies. House mice, when in the home, are resourceful at finding scraps, crumbs, or other food right from the home. Although they certainly do come and go from the structure, if a home has food available, a house mouse may never leave the structure and will rely on the food inside the home for them. Fun Fact: mice don’t need a lot of water. In fact, they get most of their water from their food. 

When it comes to feeding, one of the biggest differences between the two is the deer mouse’s hoarding habit. Because they usually live in wild spaces where food may be scarce, they often stock up and store food near their nests.

Risks Posed by Deer Mice and House Mice 

Gnawing, crawling over surfaces and food items, and leaving their urine and droppings everywhere are some of the risky behaviors of both types of mice. Explore the various risks, some similar and some different by species, to better understand the ramifications of an infestation.  

Disease Transmission and Health Risks 

Both species can transmit dangerous bacteria and germs. Each can also introduce secondary pests like fleas, ticks, and lice into human spaces, which can pose additional health threats. One of the biggest concerns with deer mice is the possibility of spreading hantavirus, a condition that affects the lungs and can be fatal. House mice are less likely to transmit hantavirus but more likely to spread illnesses like salmonella.

Damage to Property 

Mice are notorious for gnawing on just about anything. Structural elements, insulation — nothing is off limits. Over time, these behaviors can cause significant property damage. Worse, when the gnawing habit affects wiring, you could end up dealing with electrical shorts or even fires.  

Preventing Infestations of Deer Mice and House Mice 

Field Mice (deer and white-footed) are less associated with sanitation and clutter issues. For field mice, exterior exclusion (such as Cat-Guard) is the best solution. House mice, however are much more dependent on solving santitation and clutter issues.  

Sealing Entry Points 

Both deer and house mice can squeeze into tiny openings. Perform regular inspections of your home and property to find any cracks or openings that might leave it vulnerable to intrusion. Seal smaller gaps and openings with steel wool and caulk or spray foam. Close off larger entry points with screening, metal sheeting, or hardware cloth. You might also consider investing in an exclusion system, which provides a long-term barrier and targeted protection for vulnerable areas. 

Reducing Attractants in and Around the Home 

House mice often look for easy access to food sources, making it particularly important to store food, including pet food, in airtight containers. Regular cleaning and sanitation indoors can help prevent house mice. Keeping outdoor spaces tidy with regular mowing, weeding, and storing firewood away from buildings can reduce the risk of deer mice and house mice alike.

When to Call Professional Pest Control 

If you see one mouse, the odds are pretty high that more are hiding out nearby. House mice and field mice are prolific breeders. Each female is capable of having 48 offspring per year. Even if you don’t see a live mouse, any signs of mouse activity can be an indicator that it’s time to call a pro. The DIY approach can be effective if you’re dealing with a single mouse or preventing infestations, but a larger-scale mouse problem can be very challenging to combat on your own.  

Signs You Need Professional Help 

Having just a single mouse in the house is rare. Worse, deer mice and house mice are both known to reproduce very quickly, which can further complicate things. If you see any of the following signs, consider calling Catseye Pest Control as soon as possible:

• Live Mice: You often see these nocturnal critters at night, typically in out-of-the-way areas that don’t get much foot traffic. 
• Mouse Droppings: These small pellets look similar to grains of rice and are dark brown when fresh and gray-brown when older. 
• Noises: Mice often make scurrying, scampering, and rustling sounds in walls, attics, and other areas where they like to hide. 
• Nests: Mouse nests can look like ball-like structures or loose piles of materials like insulation, plant matter, fabric, and paper. 

Benefits of Professional Mouse Control 

Professional mouse control removes all the guesswork from the equation. Trained, licensed technicians can identify the type of mice you’re dealing with, how and why they are getting inside, and steps you can take to prevent future issues. Additionally, professional mouse control from Catseye Pest Control gets tailored to the unique conditions in and around your home. This customized approach ensures maximum effectiveness while keeping everyone safe.  

Call Catseye Pest Control to Keep Mice Out of Your House 

Deer mice vs. house mice — the difference matters, but no matter which species you’re dealing with, you need to partner with experts who can handle the issue. Catseye offers industry-leading mouse control services that begin with a free inspection and end with your peace of mind. Identifying pests, providing tailored treatment plans, disinfecting and repairing affected areas, and providing preventative tips are what our expert technicians are trained to do.   

Contact Catseye Pest Control to learn more or to schedule a free inspection to take control back from the inquisitive critters invading your home. 

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In last week’s episode we explored the wonders and perils of migratory Monarchs in the eastern and western regions of the US. Although the journeys of the Monarchs are remarkable, these are not the only migratory visitors to the DMV. This week we meet several other sojourners that make annual warm-weather visits to our temperate region in spring and summer, and then beat a hasty retreat when old man winter warns of chilly days and nights ahead. For the past several weeks in my rapidly fading perennial flower bed, bedraggled zinnias provided some last-minute meals for peripatetic pollinators before they get out of town in advance of a killing frost. One of my absolute favorites is the beautiful Common Buckeye. It arrives in the DMV in the spring and early summer as a migrant from its overwintering redoubts in southern states, where it has three generations each year. During the warmth of summer, females lay eggs and attendant caterpillars consume plantains, foxgloves, figworts, and verbenas. After completing two generations in our region, adults tank-up on nectar from late blooming flowers like my zinnias before heading south.

Late in autumn, bedraggled zinnias provide much needed nutrients for migratory butterflies before they embark on journeys to overwintering grounds in the south. Recently, this pretty Common Buckeye made daily visits to some fading zinnias in preparation for its journey. Not one to wait for Halloween, an orange and black Variegated Fritillary stopped by earlier this season to sip nectar from a cone flower. This pretty Painted Lady also visited the garden before heading south for the winter. And butterflies aren’t the only migratory insects found in your garden. Did you know that Large Milkweed Bugs you see on your milkweeds also head south for the winter before returning to the DMV next spring?    

Another lovely visitor to our region is the pretty Variegated Fritillary. This member of the orange and black Halloween ensemble also arrives in later spring and early summer in the DMV. It enjoys as many as three generations before heading south for the winter. Unlike larvae of the buckeye, I often find variegated fritillary caterpillars in my gardens. Several years ago, I willingly surrendered the battle to maintain a lawn as a monoculture of exotic grasses and now, floristically speaking, my yard has become quite diverse. Among the winners in the ground cover competition, particularly in shady spots and landscape beds, violets rule. With regularity, I notice significant nibbles and bites at the margins of the omnipresent violets, and regularly discover glorious larvae of the Variegated Fritillary.

Whether munching leaves of hooded violets or petals of a pansy, variegated fritillary caterpillars find these members of the Viola clan delectable. Adults love to nectar on cone flowers in the summer and can be seen in late autumn basking in the sun among fallen leaves before heading south for the winter.

Last week I also had the good fortune to spot a Painted Lady on my zinnias. This lady has been called “the planet’s most cosmopolitan butterfly” by virtue of its worldwide distribution. It is found on every continent except Antarctica. Painted Ladies also colonize the DMV each year from their overwintering grounds in Mexico and the southern US. Painted Lady caterpillars can be found on members of the Asteraceae like thistle and burdock, mallows including hibiscus, and a few other herbaceous plant families.  I’ve often thought that the eastern Monarch butterfly sets the standard for long distance migrations with its annual 3,000-mile trip to Mexico. Scientists in Europe discovered that the Painted Lady travels some 9,000 miles on its multigenerational annual migrations between Africa and Northern Europe. Wow!

Are butterflies the only migratory six-legged sojourners in the DMV?  Not at all. Several other insects conduct annual migrations to our region in spring and head south from the DMV to escape a frosty, wintery death. One common migrant familiar to milkweed enthusiasts is the Large Milkweed Bug.  This red and black harlequin arrives from the south in late spring and early summer. Adults lay eggs on milkweed pods and immature stages called nymphs use sucking mouthparts to obtain vital nutrients from developing milkweed seeds. As milkweed wane in autumn, Large Milkweed Bugs migrate to warmer zones. With record warmth here in the DMV and some flowering plants still providing rewards of nectar and pollen, you may yet have a chance to see some of these migratory wonders before they hit the road or, more accurately, take wing for refuge in the sunny south.          

Acknowledgements

References for this week’s episode include “Caterpillars of North America” by David Wagner, “A Swift Guide to Butterflies of North America” by Jeffrey Glassberg, Maryland Biodiversity Project, “Featured Creature, common name: common buckeye, scientific name: Junonia coenia Hübner (Insecta: Lepidoptera: Nymphalidae” by Jaret C. Daniels, “Direct and correlated responses to selection among life-history traits in milkweed bugs (Oncopeltus fasciatus)” by J. O. Palmer and H. Dingle, and “Multi-generational long-distance migration of insects: Studying the painted lady butterfly in the Western Palaearctic” by Constanti Stefanescu and 26 other scientists.  

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In the Northeast United States, flying squirrels are one of the three most common squirrel species. Despite their name, these quirky, slightly unusual-looking critters don’t actually fly. Instead, they use special parachute-like membranes called patagia to glide through the air for distances as far as 300 feet. The squirrels have a patagium on either side, stretching between its fore and hind limbs.  

These creatures’ large eyes help them see at night, and researchers have even discovered that all American flying squirrels emit a fluorescent glow in the dark. Discover more about where flying squirrels live and the steps you can take to prevent flying squirrel infestations in your home and on your property.  

Natural Habitat of Flying Squirrels 

Two types of flying squirrels call the Northeast home. The less common northern flying squirrel has belly hair that is gray at the base and is an average size of 10 to 12 inches. Southern flying squirrels, which are more common, typically reach lengths of eight to 10 inches and have all-white bellies. Where do these curious creatures typically live? Let’s explore their natural habitats and behaviors.  

Where Flying Squirrels Live in the Wild 

Southern flying squirrels are common along the Eastern Seaboard, from south Florida to the southern portion of Canada. They also extend as far west as parts of Texas and Minnesota. Northern flying squirrels are more common along the West Coast, although they occasionally make an appearance in the East. 

Flying squirrels typically nest in areas like woodpecker holes and abandoned nests from other animals. They thrive in forests and woodlands with plenty of trees that produce nuts, one of the staples of these omnivores’ diets. Flying squirrels also eat seeds, berries, mushrooms, small birds, moths, and beetles. 

How Flying Squirrels Adapt to Changing Seasons 

Flying squirrels don’t hibernate, but they do tend to change their habits during the cold weather months. In winter, food stores are typically sparse. These squirrels usually nest together, often in tree cavities, where they can help keep each other warm.  

Why Flying Squirrels Become a Nuisance in Homes 

Cozying up together in nests isn’t the only way flying squirrels adapt to changing seasons. These animals also move indoors to find a safe spot away from predators to raise their young. Additionally, they may move in during their mating seasons of late winter (northern flying squirrels) and early spring (southern flying squirrels). Although they can sneak into homes at any time of year, they tend to be more active in winter and mating seasons. 

Flying Squirrels in Homes 

When they move into human structures, flying squirrels can cause quite a nuisance. Because they are active at night, you might hear odd noises when you’re trying to sleep. You might also notice widening holes and cracks and new damage to siding or roofs. 

Common Areas in Homes Where Flying Squirrels Nest 

Flying squirrels are smaller than other species and can fit through relatively tiny openings. These rodents often gain entry through small cracks and holes near attic or ridge vents, eaves, or dormers. They can also enter through chimneys and other preexisting cracks. Flying squirrels commonly nest in out-of-the-way spots like crawl spaces, attics, and wall voids. 

Damage and Risks of Flying Squirrel Infestations 

Compared to other animals, the risks associated with flying squirrel infestations are minimal. However, they can potentially introduce other pests like mites and fleas into your home. They may also do some very real damage to structural elements and wiring.  

Potential Damage to Your Home 

Nuisance noises during flying squirrel’s nighttime activities aren’t the only downside to a flying squirrel infestation. They also tend to enlarge the entry points they use to come and go, leading to widening cracks and new holes in areas like walls and siding. Additionally, flying squirrels often chew on insulation and gnaw on wires, which can pose a fire hazard.  

Health Risks Associated with Flying Squirrel Infestations 

Flying squirrels aren’t known to transmit rabies. However, they can be carriers of several potential pathogens that pose health risks, including the bacteria that causes typhus. This infection causes symptoms like fever, vomiting, headaches, and a painful rash. Other possible health risks include:

• Salmonella 
• Leptospirosis 
• Parasitic infections 
• Lyme disease* 

*Flying squirrels can carry ticks, including black-legged ticks, which transmit Lyme disease. 

Preventing Flying Squirrel Infestations 

Performing property maintenance and reducing the number of things attracting flying squirrels to your property can help prevent them from moving onto your property. Explore a few preventative steps you can take to help reduce the odds of a flying squirrel infestation.  

Sealing Entry Points 

Sealing the gaps, cracks, and openings through which flying squirrels gain entry to your home is among the most effective things you can do. Be sure to cover chimneys, vents, and louvers with screening or hardware cloth and repair damaged wood around rooflines and other exterior elements. 

Reducing Attractants Around the Home 

If flying squirrels come in search of their other needs, such as access to food, they may just stay to find shelter near their food sources. Some ways to prevent that include the following: 

• Cover gardens and crops with mesh or install fencing. 
• Eliminate bird feeders or move them far from homes and outbuildings. 
• Plant any nut- or fruit-producing plants far from the home’s exterior. 
• Pick up any fallen fruit and nuts from trees.  

Yard Maintenance to Deter Flying Squirrels 

Keeping the yard mowed and reducing any outdoor clutter can help reduce the chances that these unique animals will visit your property. Another effective way to prevent them from gaining access to your home is to trim any tree limbs away from the exteriors of buildings. Trim trees and shrubs about six to eight feet away from structures, at a minimum. Doing so will help keep these adept climbers from using them as a runway to get inside.

When to Call a Professional 

So, you suspect you have a flying squirrel infestation. Now what? 

Signs You Need Professional Help 

Signs of flying squirrels include spotting gnaw marks, suspicious droppings, and widening or new holes in siding, floors, or walls. If you hear activity, it will likely be at night, as they are nocturnal creatures.  

If you suspect you have a flying squirrel in your attic or another area, you should call for professional help as soon as possible. Even if you succeed in evicting one squirrel, there is no guarantee that more flying squirrels aren’t living there. Worse, you may inadvertently separate parents from their young.  

Benefits of Humane Removal by Pest Control Experts 

Professional pest control experts can assess where and how flying squirrels are entering your home. They can identify the animals you are dealing with and determine the best strategy to remove them. Technicians have high-level training and will be able to tell if the flying squirrels have recently had babies, which will change the plan. When you rely on experts, you can rest assured that the job will be done correctly, and the flying squirrels will remain safe.  

Additionally, experts have the right equipment to protect both themselves and the flying squirrels throughout the process.  

Contact Catseye Pest Control to Help Keep Flying Squirrels Out of Your Home 

Flying squirrels can be amusing to watch if you are ever lucky enough to see them in action outdoors. When they move from their natural habitats into your outbuildings or home, they can cause more than a few problems. Flying squirrel removal is not a DIY prospect. For safe, humane, effective service you can count on, contact Catseye Pest Control to learn more or schedule a free inspection to get started. 

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A recent road trip took Bug of the Week to Beavertail Lighthouse, iconic guard to the entrance of Narraganset Bay, Rhode Island. This historical lighthouse, located in Beavertail State Park, is a stopover point for eastern migratory monarch butterflies as they wend their way from the northernmost breeding grounds in eastern North America en route to their winter retreats thousands of miles away in the mountains of Mexico. Recently, scientists have added Beavertail State Park to a growing list of locations where monarchs are recorded and tagged to track the movement of these peripatetic wonders. Our arrival late in October missed the peak of the monarch stopover, but during the course of our visit, we watched a dozen or so monarchs heading south across Narraganset Bay. On a windswept afternoon, we were lucky to see one lonely voyager hunker down for a rest in a thicket of forlorn perennial flowers. A recent status report provided by Dr. Paula Shrewsbury of the University of Maryland brings us up to speed on the status of monarchs in North America. Here is the report in its entirety. 

The Beavertail Lighthouse at Beavertail State Park in Rhode Island is a great place to watch Eastern migratory monarchs heading south to their overwintering grounds in Mexico.   

“Monarch butterflies, Danaus plexippus (family: Nymphalidae), are one of, if not, the most well-known butterflies in North America. There are few children who make it through school without learning the lifecycle of these beautiful and interesting iconic butterflies. There are community science projects and numerous other programs with the goal of monitoring and conserving monarchs. Everyone loves monarchs and rightly so. They have one of the most fascinating lifecycles and migratory behaviors of all insects. In addition, monarch adults provide pollination services and the caterpillars are food for other organisms. Given all of this I think they qualify as a “beneficial” even if the caterpillars make milkweed plants look a little ratty. 

Monarchs have an amazing lifecycle that involves multiple generations and migration across miles. In North America (NA), in general, there are three populations. There is the eastern NA Monarch population that overwinters in Mexico, and in the spring, around mid-March, begins its seasonal migration to the north toward southern Canada traveling a few thousand miles. Monarchs undergo multiple generations during this long journey to Canada. In the late summer–fall months, monarchs begin their migration back to their overwintering habitat in the oyamel fir forests in central Mexico. So basically, the adults that return to the overwintering roost in Mexico at the end of the season are several generations later than those that began the journey (ex. their great, great,… grand-butterflies). There is also a western NA Monarch population (west of the Rockies) that similarly migrates between sites in California and Canada. They overwinter or roost in coastal regions of California, migrate to Canada, and back again to California to overwinter. A few winters ago, in December, I was fortunate enough to visit one of the overwintering roosts of monarch adults in Monterey, CA. A truly amazing site that I recommend you all put on your bucket list to experience. A third, more recently founded population that is non-migratory, is in Florida and Georgia.  

You have likely heard discussion regarding monarch butterfly decline – in both the Eastern and Western monarch populations. Scientists studying monarch butterflies implicate several factors that come together to threaten populations of monarchs. Illegal logging of the forests in Mexico has reduced optimal overwintering habitat for monarchs. Weather events associated with climate change also threaten monarchs. In 2002, unusual weather in the mountains of Mexico killed an estimated 75% of monarchs that were overwintering; in 2015-2016, a winter storm killed more than 7%. These weather events killed tens of millions of overwintering monarchs. Within the U.S., Eastern monarchs have lost an estimated 165 million acres of breeding habitat along their migration route northward. Although monarch butterflies feed on nectar from a diversity of flowering plants, monarch caterpillars only eat milkweed foliage. Scientists believe that critical milkweed resources used by caterpillars have been dramatically reduced due to the use of herbicides and genetically modified crops that tolerate direct spraying of herbicides and kill milkweed. Other threats to their populations include habitat fragmentation and destruction, urban development, and pesticides, along with other climate change related phenomena.  

What is the status of Monarch butterfly populations now? The 2023 annual accounts of the Eastern monarchs that spend the winter in Mexico showed a 22% decline from 2022 counts. The Eastern monarch populations have declined by around 90% since the mid-1990’s. Western monarchs overwinter in forested groves on the coast of California. Western monarch overwintering “Thanksgiving” counts were conducted from November 11 through December 3, 2023 with a total count of 233,394 butterflies across 256 sites in California. The 2023 Thanksgiving count was slightly lower than the 2022 counts, but similar to those of 2021 (Xerces, Jan. 2024). The 2023 Thanksgiving count was followed by a “New Year’s” count (2024) that indicated the highest seasonal decrease on record, likely due to severe winter storms on the west coast. We will have to wait to see what the 2024 Thanksgiving count shows. The Western monarch overwintering population remains at about 5% of what it was in the 1980’s. Scientists say that monarchs are at risk of extinction in North America. 

Amidst the eucalyptus and pines, western monarchs brave the maritime chill on the Monterey peninsula.

What can be done to help monarchs? Globally, efforts to slow (and hopefully stop) climate change, conservation of food resources for adult and larval monarchs, and improvement of habitats for monarchs will help. Actions to influence policy on climate change, pesticide use, and the placement of monarchs on the Endangered Species Act list will also assist monarchs. At a local level, providing habitat with milkweeds for caterpillars and nectar resources for adults should improve monarch reproduction and survival. There are 73 species of milkweed in the U.S., monarch caterpillars use about 30 of these as hosts. Be sure to consult references to learn what milkweed species work well in your geographic region. Here in Maryland, species including common milkweed (Asclepias syriaca), swamp milkweed (Asclepias incarnata), butterfly weed (Asclepias tuberosa), whorled milkweed (Asclepias verticillata), and poke milkweed (Asclepias exaltata) are good choices. Research has determined that tropical milkweed, Aesclepias curassavica, is not a good choice and can actually be detrimental to monarchs. Adult monarchs feed on nectar from a diversity of plants, but not all nectar is created equally. Consult references to learn what plants provide the best nectar for monarch butterflies and their bloom times. Regional references for milkweed plants can be found at this link https://xerces.org/milkweed and references for monarch nectar plants can be found at this link https://xerces.org/monarchs/monarch-nectar-plant-guides. 

Research from the lab of Dan Potter (with student Adam Baker, UKY) shows that garden design is important and suggests how to build more effective monarch butterfly gardens. For example, monarch eggs and larvae were 2.5 to 4 times more abundant in gardens with milkweeds planted around the perimeter as opposed to gardens in which milkweeds were surrounded by or intermixed with the other non-milkweed plants. They also found female monarchs laid significantly more eggs on standalone milkweed plants as opposed to milkweeds that were visually “camouflaged” or physically blocked by adjacent non-milkweed plants. Although planting any milkweed and nectar hosts for monarchs will be helpful, these studies provide guidelines to design gardens that are more effective. Start planning for how to include milkweed and monarch nectar plants in your perennial gardens next spring. We have a critical role to play in conserving these remarkable travelers.”

Research indicates that milkweeds planted along the perimeter of butterfly gardens had 2.5-4 times more monarch eggs and larvae than those planted in the interior. So, if you want lots of monarch caterpillars and butterflies, plant the milkweeds at the edges of pollinator gardens.

 Acknowledgements 

Bug of the Week thanks Dr. Shrewsbury for granting permission to reproduce her story for this week’s episode. The great study “Configuration and Location of Small Urban Gardens Affect Colonization by Monarch Butterflies” by Adam M. Baker and Daniel A. Potter was a key resource for this episode.  Thanks also to Carol and Brian for helping us observe migrating monarchs at Beavertail State Park.

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