CHAPTER 12
Insects not only inspired this floral riot, but complemented it with life and color of their own.—Madson 1982
Thus while fire itself imparts relatively little predictability to grasshopper community dynamics in periodically burned prairie, such dynamics are nevertheless to a limited degree predictable.—Evans 1988a
The composition of the grasshopper community at a given location depends on the species composition of the plant community.—Kaufman et al. 1998a
All of these arthropod variables were significantly positively correlated to plant species richness in the fields.—Siemann et al. 1999
It appears that the main question of whether to burn or not burn tallgrass prairie out of concern for prairie-insects does not have a simple answer.—Larsen and Work 2003
[D]ifferences in insect communities between native and restored prairie may best be explained by the presence of insect host plant rather than by whether a site is native or restored.—Nemec and Bragg 2008
IN MY DAY JOB, I’m supposed to be focused on grassland birds, especially pheasants. However, 90 percent or more of the calls I’ve received from the public in the last few years have been about pollinators. That’s fine, because good pollinator habitat is also very good pheasant and songbird habitat. All of them are dependent on a diverse and productive plant community.
A chapter on prairie insects can start where the chapter on prairie birds left off. Insects play many roles in grasslands, but one of those roles is to provide food for birds and other wildlife. Insects have a high protein content, important for egg-laying hens and fast-growing chicks.
Larger grassland birds such as pheasant and prairie-chicken hens need to eat tens of thousands of insects to gain enough protein to lay a clutch of eggs. Newly hatched pheasants and prairie-chickens weigh about six tenths of an ounce. Just a few weeks later they are adults weighing up to two pounds. That’s a large amount of growth in a small amount of time, requiring a lot of protein-rich invertebrates.
Pheasant chicks consume invertebrates from seventeen different families of insects (Doxon and Carroll 2010). Each family may have scores of species. The most common insects were bees and beetles. In the shortgrass prairie of southwest Kansas, lesser prairie-chicken broods spend most of their time in areas with high densities of invertebrates. These also happen to be areas with high densities of forbs (Jamison et al. 2002; Hagen et al. 2005). In Nebraska, pheasant broods selected sites with greater forb diversity (Matthews et al. 2012). Birds are able to find where the insects are and stay there. Presumably grassland birds in the tallgrass prairie are able to do the same. Therefore, because of the vital role insects play in their diet, gamebird and songbird management may actually be more about insect management. That said, insects do far, far more in the prairie than feed birds.
Pollinators get a lot of attention these days due to: colony collapse in the economically important honeybee, concern over the shrinking monarch populations, and a focus on overall native pollinator diversity. Invertebrates play many roles on the prairie. Insects, such as bees and butterflies, are pollinators. Some insects, such as grasshoppers and leaf hoppers, are herbivores. Other invertebrates, such as spiders, are predators. Still others are parasites.
Getting back to one of the themes of this book, pollination is often held up as a prime example of cooperation or mutualism in nature. Plants give insects nectar, insects pollinate plants, and everyone is happy.
It’s not that simple. Plants give insects nectar as a reward for visiting them, picking up pollen, and then going to another flower of the same species to deposit the pollen. If the plant gives the insect too much nectar, the insect won’t be hungry anymore, will quit, and won’t deliver pollen to the next plant. If the plant doesn’t produce enough nectar, the insect won’t get enough of a reward and will stop visiting that flower. Plants also need to keep the insect from visiting other species. Picking up pollen from a blazingstar and delivering it to a goldenrod won’t benefit either plant. This is another form of plant-plant competition. Other plants have flowers that look like female insects. Males visit these flowers, try to mate, inadvertently collect pollen, and then fly off to try and mate with the next flower.
Insects don’t purposefully collect pollen in many cases. They accidentally pick it up while drinking nectar. Some insects find it easier to chew into the base of the flower, sipping the nectar but never picking up any pollen. Ideally, a plant would want its pollen spread as far as possible. The insect wants to expend the least amount of energy and visit the next closest flower. Pollination looks like a cooperative venture, but only if it’s given a quick glance. A closer inspection shows that, if not a battle of weapons, pollination is definitely a battle of wits. As Gary Larson (1998) writes in his ecological classic There’s a Hair in My Dirt, “In a field of flowers, all is fair in bugs and war.”
The previous chapter highlighted the idea that there were few prairie birds, but that each prairie bird had a specific habitat type. There are nine common and three uncommon grassland dependent birds at Konza Prairie (Kaufman et al. 1998a). There are 307 insect species that have been identified on Konza Prairie, but only about 10 percent of the species have probably been documented (Kaufman et al. 1998b). This means that there are probably at least three hundred insect species for every bird species.
Even that is almost surely an underestimate, maybe by an order of magnitude or more. In Hidden Prairie, Chris Helzer (2020) spends a summer photographing one square meter of restored prairie in Nebraska. Over the summer he recorded ninety-seven species of invertebrates, including twenty-two flies, eighteen beetles, fourteen bees, seven true bugs, seven spiders, four wasps, five ants, and five hoppers (C. Helzer, pers. comm.).
Even those numbers need to be put in context. Helzer was very clear in his book that this was a photographic effort, not a comprehensive scientific effort. A thorough scientific study would surely reveal many more species in that square meter. Imagine what a survey of even a one-acre remnant prairie might reveal when it comes to invertebrate diversity.
On the western edge of the tallgrass region, there are at least forty families of beetles, including sixteen plant eating, nine predator, seven fungus eating, six scavenger, and one gatherer family. There are six families of grasshoppers, and within the short-horned grasshopper family, there are at least twenty-six species (Jonas et al. 2002). There are a lot of invertebrates out there. However, like plants, a simple count of species doesn’t really tell us much about the ecology or conservation of prairies.
Studies of several groups of insects generally show that there are common species and rare species (Bomar 2001; Kwaiser and Hendrix 2007; Moranz et al. 2012). Perhaps because so many insects are so closely tied to specific plants, it’s not surprising that they follow a pattern similar to the Core-Satellite Hypothesis (Kaufman et al. 1998b). Each prairie remnant is a unique community of plants and the same applies to insects. Tonietto et al. (2017) titled their study “Bee communities along a prairie restoration chronosequence: similar abundance and diversity, distinct composition.”
Several studies show that insect communities are closely tied to the plant community in general (Evans 1988b; Siemann et al. 1998; Nemec and Bragg 2008; Tonietto et al. 2017). There is also a strong relationship between the abundance or density of flowers and insects (Kwaiser and Hendrix 2007; Harmon-Threatt and Hendrix 2015), as well as complex relationships among the invertebrates within the prairie and even within a single plant.
[L]ocal arthropod herbivore diversity may also be maintained by and, in turn, maintain a diversity of parasites and predators that prevent competitive exclusion, allowing a high diversity of herbivore to coexist on even a single plant species. (Siemann et al. 1998)
Stepping down from the plant community, and building on the idea that a single plant species can host a high number of invertebrates, we can look at individual plant and insect species. Most schoolkids know that monarch butterflies are closely tied to milkweeds. However, many insect taxonomists have taken this a step further and incorporated a plant’s name into the insect’s name. In one survey, twenty of forty-nine insect species had a prairie plant in the insect’s common name (Panzer 1988). A survey of Wisconsin prairies revealed Amorpha borer, alumroot flea beetle, iris weevil, leadplant gall-midge, Silphium aphid, sage leafhopper, cordgrass bug, leadplant plantlice, scurf-pea argid sawfly, Amorpha stem gall moth, and Liatris borer moth, to name a few. To get even more specific, some insects take the names of specific parts of a specific plant: bushclover stem-borer beetle, phlox stem borer, bluestem leaf-mining beetle, Silphium leaf-miner, spiderwort leaf beetle, Baptisia seed weevil, sunflower seed bug, Silphium internal stem gall wasp, and false boneset flower moth, among many others (names provided courtesy R. Henderson, WI DNR retired). At the end of Chapter 11, I stated that birds weren’t good botanists. Insects are very good botanists.
Other insects are closely tied to one species of plant, even if they don’t take the plant’s name. The karner blue butterfly is tied to lupine. The regal fritillary butterfly is tied to prairie violets. This may sound counterintuitive. It makes sense for a grazer like bison to focus on grasses like big bluestem because bluestem is large, abundant, and common almost everywhere. Lupines and violets are small plants scattered across the prairie. However, that’s a modern viewpoint. In previous times, violets may have provided an abundant food resource for regal fritillaries (Wilder 1935; Madson 1982).
On southern-sloping hillsides one could surprisingly note some bright morning that the birds-foot violets had turned the slope to a patch of blue like sky. (Quick 1925)
It winked with blue-eyed grass and yellow grassflower, there were acres and miles of bird-foot violet. (Peattie 1938)
If managing for a dozen species of birds is a challenge, managing for hundreds to thousands of invertebrates is far more complex. The most common management tool in prairie, fire, is especially controversial among invertebrate ecologists. Much like many suburbanites prefer a nice homogeneous green lawn, fire managers like solid homogeneous black when they are done. Many of us, myself included, have gone back after a fire and held a drip torch over every last little patch that didn’t burn. It’s always nice to have a good clean complete burn.
What that does is destroy any last little refugium for insect eggs or larvae in the thatch. It’s fine to leave a few “skips” in the middle of the burn (Panzer 1988). This may be where grazing can play another role in invertebrate conservation. Burning areas that were grazed creates a complex patchwork of burned and unburned.
Unfortunately, we can’t simply make general statements like “burning is bad for butterflies” or “grazing is good for grasshoppers.” With insects, it’s especially important to know what the questions are. Are we interested in the effects of management on insect diversity? Are we interested in overall insect abundance or abundance of a particular species or group of insects? Is the management targeted at a population of one specific insect species? Are we interested in the immediate response of the species to the management? Or are we looking for a response two or three years later? The science is quite mixed relative to fire and insects.
Greatest species diversities [grasshoppers] occurred on sites subjected to intermediate frequency of fire. (Evans 1984)
[S]ome species were more abundant the year immediately following the burn, while others were found in greater abundance in areas with increased time since fire. (Larsen and Work 2003)
[B]utterfly abundance was lowest in the burned only restoration practice. However, we found that butterfly diversity was highest on these burned only sites. (Vogel et al. 2007)
In one study, 40 percent of insects were fire-negative and 54 percent were fire-positive or fire-neutral (Panzer 2002). The next question is what fire-negative means. If there’s an immediate drop in a population but the population recovers within a year or two, then the negative effects are short-lived. If the fire drives a local population to extinction and there’s little opportunity for recolonization, that becomes more of a problem.
This fire/no fire may be a false debate. Fire will kill individuals, but lack of fire will kill the prairie they depend on. Panzer (2002) points to some entomologists who would like to see burning reduced or eliminated. At the same time botanists are calling for the same level or increased burning to maintain natural processes, combat invasive plants, or remove woody vegetation. This controversy around fire creates what some researchers call the prairie butterfly paradox (Moranz et al. 2014).
Absent frequent disturbance, remnant tallgrass prairie rapidly converts to a dominant cover of woody plants. This creates unique challenges for conservation of prairie-specialist insects. . . . Regal fritillary butterflies (Speyeria idalia) exemplify this problem, with sharp population declines in recent decades and considerable disagreement on management practices, particularly the use of prescribed burning to maintain habitat. (R. A. Henderson et al. 2018)
Inconsistencies among findings have only heightened the confusion behind what is commonly referred to as the “prairie butterfly paradox,” where butterflies like the regal [fritillary] appear to be sensitive to the very processes considered necessary to maintain their grassland habitat. (McCollough et al. 2019)
Insects need a place to lay eggs, grow into adults, and then they need abundant pollen and nectar sources once they are adults. At some sites “regal fritillaries deemed recently burned units more suitable” than unburned prairie (Moranz et al. 2014). This is undoubtedly because burning stimulates flowering of many species of prairie forbs. Adult foraging habitat may be more critical than host plants for prairie butterflies (Panzer 1988). Eggs don’t do well in burned areas, but burning dramatically stimulates blooming of most prairie wildflowers. Within each grassland, pollinators need a mix of unburned prairie for the juvenile stages of their lives and prefer burned prairie full of flowers for the adult stage of their lives.
In Pennsylvania, frequently burned grasslands had a higher probability of supporting the violets that regal fritillaries depend on (Adamidis et al. 2019). The researchers also point to direct effects of fire, such as mortality of immature butterflies, and indirect effects, such as host plant and nectar plant abundance, vegetation structure and composition, as largely unknown in telling the full conservation story for many species. Often the most useful management tool is “creating and maintaining high quality habitat with abundant violets (Viola spp) and varied nectar sources” (R. A. Henderson et al. 2018). They also determined that quality habitat is more important than reducing fire, a goal that can be met with burning every three to five years.
It’s always been accepted as common wisdom that insects that are in the plant canopy during a fire during a stage in their life when they can’t move, such as eggs or larvae, will face nearly 100 percent mortality in a fire. Therefore fire is a negative because it kills individual insect eggs, larvae, and pupae. However, regal fritillary larvae can survive at least some fires (McCullough et al. 2017). Perhaps some larvae or eggs are low enough in the leaf litter that the fire goes right over the top of them. By contrast, insects that overwinter as eggs in the soil may be stimulated by the sun-warmed soils in the days after a fire.
Along with fire, grazing also affects invertebrates. Grasshopper densities for seven of nine of the most common grasshoppers in Kansas responded positively to grazing (Joern 2004) and there were 45 percent more grasshopper species in grazed areas than ungrazed prairie (Joern 2005). Grazing increases forb diversity, which benefits the forb-feeding species. Grazing can also keep grasses short, tender, and succulent, which may benefit the grass-feeding insects.
We can relate modern conservation back to historic landscape patterns with regal fritillaries and other invertebrates. If there are other unburned prairies within a reasonable dispersal distance from the burn, then invertebrates should readily recolonize the area after the fire (Moranz et al. 2014; R. A. Henderson et al. 2018). Unfortunately, in today’s world many of our small remnants are so isolated that there aren’t other grasslands, native or restored, within a reasonable dispersal distance.
Today, managers are encouraged to break up burns into many small units so that there’s always some unburned vegetation nearby. In some of the historical descriptions of fire in Chapter 4, observers describe fires running for mile after mile after mile. Where were the refugia for insect eggs and larvae during these fires? How did invertebrates recolonize the center of these large burns?
Similar to burning, another factor is mowing. Some will argue that haying or mowing is a good alternative to fire that is less detrimental to insects. However, especially in the northern states, there can be conflict between the ornithologists and entomologists when it comes to mowing.
In Minnesota, several of my colleagues and I have noticed that monarchs prefer to lay eggs on younger common milkweeds that regrew after landowners mowed or hayed the field in mid-summer. Older milkweeds, in areas that were not mowed, can be tough and leathery by the time monarchs make it to the northern end of their range. There are similar patterns of monarchs using the succulent milkweeds that regrew after a summer fire in Oklahoma (Baum and Sharber 2012).
Some monarch advocates, especially in northern states, would like to see mowing of roadsides and hayfields in early summer so there’s sufficient time for the milkweeds to regrow by the time the monarchs arrive. However, that would be at the peak of the nesting season for birds. Bird advocates would like to see mowing and haying done in mid- to late summer after bird nests have hatched and the young are old enough to escape the mower. That is the peak of the monarch egg-laying season in northern latitudes. As is often the case with prairies, there are no easy answers.
Fire and grazing, two factors managers can exert some control over, clearly affect invertebrate diversity and abundance. The third factor cited when discussing the prairie is of course the weather. Daily, weekly, and seasonal vagaries of local weather patterns obviously affect insect populations. However, events practically on the other side of the globe can affect prairie insects. The North Atlantic Oscillation correlate to annual changes in grasshopper populations in Kansas (Jonas and Joern 2007). Weather literally on the other side of the world can affect insects in the prairie.
Hundreds to thousands of invertebrates may be affected, directly or indirectly, to a greater or lesser extent, and independent of other species by fire, grazing, and climate. We know generally what will happen if we burn a prairie. We know generally what will happen if we don’t burn a prairie. But those generalities and the unknown variability within those generalities become problematic especially when discussing rare, threatened, or endangered species on small prairie remnants.
Pollinators and other invertebrates will probably be a focus for grassland restoration in the future. Diversity in general is important. However, there may be key species that are especially important to pollinators, such as leadplant, purple prairie clover, yellow coneflower, and golden alexanders (Harmon-Threatt and Hendrix 2015). These four species in restorations seem to be disproportionately important to pollinating insects. Also, when thinking about restorations and invertebrates, the surrounding landscape may be just as important as the actual restoration site (Hines and Hendrix 2005; Kwaiser and Hendrix 2007; Nemec and Bragg 2008; Griffin et al. 2017).
As with everything in prairie management, the simple answer is to not do too much burning or haying or grazing at any one time in any one place, but don’t do too little either. How do we manage for prairie insects? Do a little bit of everything, but not too much of any one thing.
Two Worlds
I HAVE TWO FEARS about both myself and the conservation community, and time to think about those fears as I sit in the back of a legislative hearing room this morning. I swore it would never happen to me. I’d spend my life in the field with a clipboard, binoculars, and a good dog by my side collecting data and later analyzing data with the pup asleep under my desk. Yet here I am, working in a cubicle in a big building in a large city in a job that revolves around policy, economics, meetings, hearings, budgets, paperwork, forms, politics, plans, and more meetings. And I’m wearing a tie!
Every passing month I feel more and more disconnected from the grasses, wildflowers, and prairie wildlife I’m supposed to be focused on. I used to be a pretty good botanist. Anymore, I really struggle with a lot of common and Latin names when I do get out. “Looks familiar . . . used to know that one . . .” I’m afraid I’ve lost touch, and that’s not good.
My other fear is that people out in, what I like to call, the real world don’t understand all the policies, politics, economics, and associated administrivia it takes to make conservation happen. We head to the natural world as a refuge from the vagaries and doldrums of daily life, whether that refuge be a camping tent, canoe seat, duck blind, deer stand, or a path through prairie flowers and grasses. However, to continue to engage with the natural world, we also have to engage with the politics and economics of conservation. Too often, people don’t want to get involved.
So here I sit, waiting to present my proposal for funding my program. It’s an odd situation. I think of all the other presenters in the room as colleagues and friends. Today we are competitors for the same funds, but in a collegial and friendly way.
Biodiversity, or diversity, is a commonly used word. There’s another type of diversity that gets much less attention: people. We need people to join conservation organizations and pay their annual membership. We need hunters to buy hunting licenses and stamps that go to habitat management. We need people to call local, state, and federal legislators and have their voices heard. We need researchers at federal and state agencies, at universities, and working for conservation groups. We need people with specialized training and skills to safely conduct prescribed fires, restore wetlands with bulldozers, and all the other habitat management that needs to get done. We need lobbyists and policy specialists. We need lawyers who can, when needed, file suits against those who wish to destroy habitat. Most importantly, we all need to support one another.
Perhaps we need the conservation population to look like the American population. Diversity or biodiversity is mentioned at almost every meeting. However, the ethnic and cultural diversity of all the meetings I go to and people I work with, is, well, not very diverse. If conservation is going to be relevant to America’s future, then conservationists need to look more like the United States, in all of its glorious diversity.
It would be great to just live out on the prairie, listening to the wind, collecting and planting seed. Unfortunately, the decisions, the economics, the policies, and the politics that affect wildlife and habitat are rarely made out here. Those decisions are made in marble halls and hearing rooms, around conference tables, usually in large cities. For many of us, those places are as stressful as time alone with a good dog is relaxing.
It’s not enough to live in the insulated world of bluestem and just hope things are going well other places, or that others will take care of those issues for us. Just as importantly, those who do work in those places need frequent contact with the natural world to remind themselves why they do what they do. It’s pretty easy to get so absorbed in the politics and policies that we forget the ultimate goals of our efforts.
Therein lies the challenge of living in two worlds.