Category Archives: Spiders

Spiders

Black Widows: The Hermits of Door County

Spider cases at the UW Insect Diagnostic Lab often boil down to clients wondering if they’ve found either a brown recluse or black widow spider.  Wisconsin is home to approximately 500 species of spiders, and essentially all of these are harmless, beneficial creatures that provide us with an astonishing amount of free pest control*.  While we’re outside the native range of the dreaded, but horribly misunderstood brown recluse spider (Loxosceles reclusa), Wisconsin is actually home to a native black widow species—the northern black widow (Latrodectus variolus).  In Wisconsin, these spiders are rare and have been documented in fewer than 10 counties.  Most Wisconsinites will go their entire lives without seeing a northern black widow out in nature and if you’re lucky enough to spot one of these elusive creatures, you’d almost certainly encounter a lone individual.  In contrast, there are several other widow spiders that can be much more common in other parts of the country.

The vast majority of black widow records in Wisconsin are from the east-central counties.  Door county historically stands out as having the most confirmed sightings and perhaps takes the place of Wisconsin’s black widow “capital”—although only a few sightings occur in most years.  The northern black widow doesn’t seem to occur farther north under natural conditions, which suggests an inability to the survive colder winters in the northern part of the state.  Along these lines, Door county’s unique geography and the moderating effects of Lake Michigan may explain why the majority of reports come from that part of Wisconsin.  Similarly, other confirmed reports of the northern black widow tend to be from nearby counties bordering Lake Michigan.  Away from the lake, northern black widows have also been documented in prairie areas in Crawford, Grant, and Sauk counties, where the microclimate on south-facing slopes may favor their survival.

“Scarlet”—the first Northern Black Widow documented in Sheboygan County. Photo Credit: PJ Liesch-UW Entomology

In a typical year, the UW Insect Diagnostic Lab might get a report or two of black widow spiders, but 2017 stood out in the sheer number of reports.  For spiders like the black widow, I keep in touch with Dr. Mike Draney, an arachnologist at UW-Green Bay.  During some stretches of 2017, Mike and I were emailing reports of black widows to each other once or twice a week!  These reports generally came from Door county and nearby areas.  In addition, these spiders were also documented in two additional Wisconsin counties for the first time last year: Brown county and Sheboygan county.

It’s possible that winter weather patterns might explain the distinct bump in northern black widow sightings last year.  Leading up to 2017, Wisconsin faced two consecutive mild winters, which might have favored insects, spiders, and other creatures that fare better in slightly warmer climates.  While the state did see an increase in reports last year, it’s not yet known if that trend will continue in 2018 as the state just emerged from a veritable winter season.

*A recent study estimated that spiders around the globe consume approximately 400 – 800 million tons of prey annually. Nyffeler, M. & Birkhofer, K. Sci Nat (2017) 104: 30. https://doi.org/10.1007/s00114-017-1440-1

Phenology, Spiders

Signs of Autumn: Orbweavers

Without looking at a calendar, certain things tell you autumn is approaching—pumpkin spice encroaches upon your food and beverage options, weekends are filled with football, the leaves are turning various hues, and brightly-colored orbweaver spiders adorn the landscape.

A beautifully patterned shamrock orbweaver (Araneus trifolium) on the side of a Northwoods cabin. Photo Credit: PJ Liesch, UW Entomology.

Like the overwhelming majority of spiders, the orbweavers (Family Araneidae) of autumn are harmless to humans.  There are a dozen or more common species in the Great Lakes Region and these can be good sized as far as spiders are concerned—easily over 1” long when you include their legs.  Our commonest species are from the genus Araneus and include the cross orbweaver, shamrock orbweaver, and the marbled orbweaver.  They can be quite common in yards, gardens, on plants, and on your back patio.  Other common species in the genus Argiope (the “garden” spiders) are even larger, spanning over 2” with outstretched legs.  In addition to their large size, flashy “fall” colors and patterns conspicuously adorn these spiders—yellows, oranges, reds, stripes, polka-dots, and more.

Despite the large size, orbweaver spiders are harmless. Photo credit: PJ Liesch, UW Entomology.

Their life cycle is another reason why many orbweavers can be so noticeable in autumn.  Our common species overwinter in the egg sac and the young spiderlings usually go unnoticed as they grow and develop the following spring and summer.  By the time they’ve reached maturity in late summer, it’s mating season and the adults have a month or two to go about their business. During that time, they’re easiest to spot sitting in their large circular webs, which were an inspiration for the children’s classic Charlotte’s Web.

Further Reading:
Unfortunately, most folks never take the time to learn about these beautiful and fascinating creatures.  If you ask someone their thoughts of spiders, feelings of fear, disgust, repulsion, and anxiety might come to mind.  In society as a whole, there seems to be a feeling that spiders are something to be loathed or feared, which really shouldn’t be the case. It doesn’t help when the internet has an abundance of myths and preposterous stories about spiders [here’s a good source to debunk some of those myths].  In the grand scheme of things, you’re more likely to be injured by a pet dog than you are to be harmed by a spider.  If anything, spiders should be considered beneficial as they eat an astonishing mass of insects every year.

If you’d like to learn more about spiders, one of my favorite books for the Midwest is Spiders of the Northwoods by Larry Weber.  There are also some great spider blogs out there; my favorites include: SpiderBytes by Catherine Scott and Arthropod Ecology by Chris Buddle. To this day, two of my all-time favorite spider posts are from Chris Buddle’s blog and have the self-explanatory titles of “Spiders do not bite” and “Update: spiders STILL don’t bite”.

Aquatic Insects, Borers, Invasive Species, Pollinators, Spiders, Wood-attacking Insects

Wisconsin’s Top 10 Insect Stories of 2014 (Part III)

Below you’ll find the third and final part of a series describing the Top 10 insect-related stories of 2014 from Wisconsin.

4) Hexagenia Mayflies and Fishing Spiders: If you love insects and/or fly fishing, you might have been thrilled to hear about the massive mayfly hatch along the Mississippi River in late July. These emergences happen yearly, but the mass emergence in the evening of July 20th was one of the largest in decades. We’re not talking about thousands or millions of insects, but billions of insects emerging at the same time. So many mayflies emerged simultaneously that the insects showed up on National Weather Service weather radar (a history of these events can be found here).  When these emergences occur, the insects can accumulate on bridges and streets making roadways slippery.

Hexagenia 20 July 2014
Mayfly emergence on the evening of July 20th. Source: National Weather Service.

The insect involved is the Hexagenia mayfly. The young (nymphs) live in the sediment at the bottom of the Mississippi River and feed on bits of organic matter in the water. The presence of the adults above water is truly an ephemeral phenomenon; it’s even reflected in the name of their group: the Order Ephemeroptera. Adult Hexagenia mayflies only live for a matter of hours, which leads them through a frenzied courtship period. Shortly thereafter, they’re done for.

Around the same time as the mayfly emergence, the fishing spider stories made their way around television, radio, and Facebook and the phone calls and emails came flooding in. Despite the hype, fishing spiders are native to Wisconsin and can actually be fairly common. Fishing spiders aren’t truly aquatic, but they do tend to hang out near water. They’re among our largest spiders in the state, and can be large enough to capture and feed on small minnows.

3) Spotted Wing Drosophila: One of our newest invasive species had another strong year in 2014. The spotted wing drosophila (SWD) is originally from parts of Asia, and was discovered in the US in 2008. Within two years, it had popped up in Wisconsin. Like other fruit flies, SWD loves fruit.  The main difference is that our run-of-the-mill fruit flies lay eggs in overripe or spoiled fruit.  In contrast, SWD females have a hacksaw-like egg-laying structure, which can be used to slice into ripe or ripening fruit to lay eggs. As a result, SWD has become a major issue for fruit growers in the state.  Late-season berry crops (raspberries, blackberries, strawberries) are hit the hardest. SWD has been found statewide, and will continue to be a major concern for late-season fruit growers for the foreseeable future.

2) Pollinators: You don’t have to listen to the news very long before you hear a reference to pollinators. Unfortunately, much of the news on the topic paints a bleak picture: pollinators of all kinds are in decline at the moment. Honey bees, bumble bees, other native bees, and butterflies like the Monarch are all facing declines. Unfortunately, it’s not a black-and-white situation, and there’s no simple solution to the issue at hand. Instead, many different factors, such as habitat loss, diseases, parasites, land-use practices, pesticides and other factors may all be involved one way or another.

We may not think of the connection to pollinators when we visit the grocery store, but without the pollination services of insects, the produce section would be scarce. It turns out that roughly a third of the world’s agricultural crops rely on pollinators. Without pollinators, you’d have a hard time finding apples, strawberries, melons, tomatoes, and many of our common food items.

Flowering plants in your yard provide resources to bees. Photo Credit: PJ Liesch
Flowering plants in your yard provide resources to bees. Photo Credit: PJ Liesch

If there’s a silver lining to the situation, it’s that attention has been brought to the topic. In June of 2014, the White House announced the creation of a pollinator health task force to develop a national strategy to help prevent pollinator losses and help improve pollinator habitat.  While it may seem like a small step, individuals can help pollinators by making their own yards pollinator friendly. Incorporating native plants into the landscape, providing nesting habitat for solitary bees, and using caution with pesticides are all ways to help pollinators in our own yards.  Tips for accomplishing this can be found here.

1) Emerald Ash Borer: The emerald ash borer (EAB) continues to be one of the biggest insect stories in the state. This invasive pest is originally from Asia, but has been wreaking havoc on Wisconsin’s ash trees since 2008. Spread within the state seemed to progress slowly at first, but 2014 saw dramatic changes in our quarantine map in the state. In early 2014, we had a total of 21 Counties quarantined for EAB. By the end of the year, 16 additional counties had been added to the map to bring the total up to 37 counties. While most of the quarantined counties are in the southern half of the state, Douglas and Oneida counties in the north are also quarantined. Unfortunately, this destructive pest is difficult to detect and easily transported in firewood, which means that this pest will only spread and the situation will worsen over time. While we have options to protect individual ash trees (available here), we don’t have a way to protect ash trees in woodlots or forested areas. Since its introduction into the US, the emerald ash borer has killed tens of millions of ash trees. With over 700 million ash trees in the state, Wisconsin has a lot at stake.