Development and evaluation of methods to assess populations of black flies (Diptera: Simuliidae) at nests of the endangered whooping crane (Grus americana)



Hematophagous insects can negatively affect the reproductive success of their vertebrate hosts. To determine the influence of hematophagous insects on endangered vertebrates requires specially designed programs that minimize disturbance to the hosts and address problems associated with their small populations. We developed and evaluated a surveillance program for black flies potentially affecting a population of whooping cranes (Grus americana) introduced to central Wisconsin, U.S.A. In one of the few studies to survey host-seeking female black flies and their immature stages concurrently, we processed nearly 346,000 specimens and documented 26 species, of which only two, Simulium annulus and Simulium johannseni, were attracted to nesting whooping cranes. Attempts to assess black fly populations with artificial nests and real crane eggs were unsuccessful. Carbon-dioxide traps performed well in describing black fly taxa on the landscape. However, the number of black flies at whooping crane nests was consistently higher than the number captured in carbon-dioxide traps. The carbon-dioxide traps poorly described the presence/absence, population fluctuations, and periodicity of black flies at whooping crane nests. The weak performance of the carbon-dioxide traps might have resulted from microhabitat differences between trap locations and nests or from Simulium annulus and Simulium johannseni using sensory cues in addition to carbon dioxide to find hosts. Choice of trapping techniques, therefore, depends on the information required for the particular study objectives.


The development and evaluation of surveillance methods for hematophagous flies have a long history (Service 1993), driven by the need to monitor the species responsible for nuisance problems and blood-borne diseases of humans and domestic animals. In contrast, few studies have detailed the methods for surveying hematophagous flies associated with wildlife, and still fewer have evaluated those methods (Adler et al. 2004).

Among the surveillance methods used to monitor hematophagous flies are carbon-dioxide traps (Snoddy and Hays 1966, Frommer et al. 1976, Comtois and Berteaux 2005), sham-traps (Helle et al. 1992, Shipp 1985, Anderson and Yee 1995, Sutcliffe et al. 1995), landing rates on dead specimens (Lowther and Wood 1964), discomfort behaviors of hosts (Walker and Edman 1986, Cully et al. 1991, Toupin et al. 1996, Mooring, et al. 2003), simulated-ear traps (Schmidtmann 1987), and direct counts of bites on study specimens (Comtois and Berteaux 2005) and of flies on sentinel animals (Anderson and DeFoliart 1961, Lowther and Wood 1964, Fletcher et al. 1988).

We developed a surveillance program for ornithophilic black flies (Simuliidae) potentially affecting the fitness of nesting whooping cranes (Grus americana) in central Wisconsin. This crane population is the result of an introduction effort that began in 2001. From 2005, the first year that nesting occurred in this population, to 2008, little nest success occurred as a result of nest desertions. When black flies were observed at a deserted nest in 2008, a hypothesis was developed that they were causing the desertions (Urbanek et al. 2010). The surveillance program was developed to help test that hypothesis.

Black flies take blood from a broad range of avian hosts (Adler et al. 2004). Outbreaks have been linked to nest desertion by common gulls (Larus canus) (Bukacinski and Bukaciniska 2000) and common loons (Gavia minor) (McIntyre 1988), nestling mortality in red-tailed hawks (Buteo jamaicensis) (Smith et al. 1998) and purple martins (Progne subis) (Hill 1994), and fledgling mortality in great horned owls (Bubo virginianus) (Hunter et al. 1997). Wisconsin has a diverse assemblage of black flies (Anderson and DeFoliart 1961, DeFoliart et al. 1967). Some species in the state affect birds directly through nestling mortality, as in eastern bluebirds (Sialis sialis) and tree swallows (Tachycineta bicolor) (Gaard 2002), and indirectly through simuliid-borne diseases such as leucocytozoonosis in mallards (Anas platyrhynchos) (Trainer et al. 1962).

Our development of a surveillance program to evaluate black fly populations associated with whooping crane nesting had four major limitations: 1) We could not directly study black flies at active nests because of concerns that our visits could result in nest desertion. 2) We had to initiate the surveillance program before the nesting season to establish the phenology of black fly emergence relative to crane nesting. 3) Whooping cranes are among the world's rarest birds, with a total wild population of fewer than 450 individuals. We studied black flies associated with a disjunct subset of the population averaging fewer than 15 breeding pairs during our study. Combined with the limitation of one visit per nest, our study faced sample-size challenges. 4) The use of sentinel birds from more common species would provide little information relative to whooping crane nests due to host-specificity and preferences of black flies.


Study area

We investigated female black flies on or near (within 3.2 km of the property boundary) Necedah National Wildlife Refuge (NNWR), Juneau County, WI, U.S.A. (Latitude: 44.149; Longitude: –90.183). We surveyed larval and pupal black flies on the NNWR and for 10 km beyond its boundary, a distance likely to include typical dispersal distances of the females of most species (Adler et al. 2004). The study area is characterized by flat topography. NNWR has more than 200 km of drainage ditches. Two rivers, the Yellow River on the east and Beaver Creek on the west, flow north to south along the NNWR boundary, and the Lemonweir River lies south of the NNWR (Figure 1). The entire study area, including the streams and rivers, has a substrate of coarse sand. Surveys of adult black flies were conducted in shallow meadows (water depth about 60–75 cm) used by nesting whooping cranes. The meadows were dominated by sedges (Carex spp.) and bulrushes (Scirpus spp.), with patches of willow (Salix spp.) in drier areas, and were located largely in open prairie areas maintained with prescribed burning and mowing since the 1940s. The only exceptions were sedge meadows in wooded areas with black oak (Quercus velutina), jack pine (Pinus banksiana), and aspen (Populus grandidentata and P. tremuloides).

Figure 1.

Location of whooping crane (Grus americana) nests, artificial nests, and carbon-dioxide (CDC) traps in and around Necedah National Wildlife Refuge, Juneau County, WI, U.S.A.

Experimental procedure and data analysis

Approval to work in and around active whooping crane nests and to work with eggs of red-crowned cranes (Grus japanensis) and Siberian cranes (Grus leucogeranus) and body parts of whooping cranes was covered under an Endangered Species Recovery Permit (#TE048806-1). The research also was covered by a Migratory Bird Permit (#MB09144A-1).

To determine the local species pool of black flies, we surveyed all sites accessible by vehicle, both on the NNWR (representing virtually all flowing water on the Refuge) and off the Refuge (representing all flows 2 m or more in width) for 20–40 min each. In total, we sampled 57 sites on the Refuge and 20 off the Refuge at various dates from 30 March to 6 May in 2009–2011. Larvae and pupae were collected with forceps from all available substrates (e.g., trailing vegetation, leaf packs) at each site and fixed in three changes of 1:3 acetic ethanol. Identifications were made morphologically and cytogenetically, following procedures and identification keys of Adler et al. (2004).

Host-seeking black flies were collected in 2009 and 2011 with seven Centers for Disease Control (CDC) traps (CDC MiniLight Trap, Bioquip Products, Rancho Dominguez, CA, U.S.A.) established randomly in suitable whooping crane nesting habitats (Figure 1). Suitable sites were based on nest locations on NNWR from 2005 to 2008. We used ArcMap 9.3 (ESRI Inc., Redlands, CA, U.S.A.) to model suitable whooping crane nesting habitats and to select trap locations randomly. Trap locations were the same in 2009 and 2011. The distance from the traps to the nearest whooping crane nest was 1,358.7±215.8 m and 756±139.3 m in 2009 and 2011, respectively.

Traps were operated daily with the light deactivated and individually baited with about 1.6 kg of dry ice each, from 14 April to 6 June 2009 and from 11 April to 17 June 2011. The only exceptions in 2009 were days when wind or rain would interfere with trapping operations. In 2011, the traps were deployed one or two days per week, weather permitting. Thus, traps were deployed on 53 days in 2009 and on 17 days in 2011. We had a total of 343 trap nights in 2009, with 36 trap malfunctions, and 117 trap nights in 2011, with only two trap malfunctions. In both years, trapping began before the emergence of black flies. Because trap height can influence collecting efficacy (Russell and Hunter 2005, Swanson et al. 2012), we placed the traps about 150 cm above the water, the approximate height of a whooping crane's head while on a nest.

We counted female black flies at whooping crane nests by combining the results of three methods: 1) glueboards, 2) high-resolution images, and 3) specimens drowned in the contents of damaged or hatched eggs. These data were collected once, upon completion of a whooping crane nesting effort (i.e., a nest desertion or a successful hatching). We deployed 40-mm × 65-mm glueboards (Professional Pest Control, Columbus, GA) on top of the heads of sandhill crane decoys (Model Q1600, Carry-Lite Decoys, Ft. Smith, AR) painted to resemble whooping cranes. Glueboards were exposed for 5 min, following the procedure of Weinandt4. To avoid collecting black flies attracted to humans, we remained at least 25 m from the decoy during the 5-min exposure. After the glueboard sampling, we removed the decoy and obtained an image of the nest from 2 m, with a superfine-resolution (2816 × 2112 pixels) camera. Finally, we collected any damaged or hatched eggs from the nest. We summed results of all three counts by species to give a count per nest. For black flies counted on high-resolution images, we applied the species ratio from the glueboard and egg samples. When we were able to collect a glueboard sample but not a high-resolution image or vice versa, we limited black fly results to presence/absence information.

Black flies from carbon-dioxide traps were euthanized by freezing for 2 h. Those on glueboards were removed with xylene. Individuals from all samples were fixed in 95% ethanol and all specimens were counted. All glueboard and egg samples were identified to species, as were all carbon-dioxide trap samples with fewer than 120 individuals. For samples from carbon-dioxide traps with more than 120 black flies, we counted the entire sample and randomly selected 120–200 specimens for identification using a petri dish on a grid. Specimens were boiled in 10% potassium hydroxide (KOH) to remove soft tissues, washed twice in distilled water, and identified by microscopic examination of genitalic features (Adler et al. 2004). The same method was used for specimens from glueboards, with the addition of 10% mineral spirits after boiling in KOH. Representative specimens of all species were deposited in the Clemson University Arthropod Collection, Clemson, SC.

To evaluate the performance of carbon-dioxide traps for describing variability in black fly populations at whooping crane nests, we used the following comparisons: 1) black flies at a nest vs the mean number captured in all seven carbon-dioxide traps and the number captured in the carbon-dioxide trap nearest the nest, 2) positive and negative indices (presence/absence) for black flies at a nest vs seven carbon-dioxide traps and the nearest carbon-dioxide trap, and 3) correlations between the number of black flies (when present) at nests and the mean number from all seven carbon-dioxide traps and from the nearest carbon-dioxide trap. We limited these comparisons to occasions when we had results from carbon-dioxide traps on the same, previous, or following day of a nest visit. All data were log (n+1) transformed before analyses with paired t-tests (Muturi et al. 2007, Smallegange et al. 2010, Chen et al. 2011) and Spearman's rank correlation (Comtois and Berteaux 2005, Bisevac et al. 2009, Swengel and Swengel 2011).

We constructed nine artificial nests in 2010 to evaluate their performance in attracting black flies, compared with real whooping crane nests (Figure 1). To mimic whooping crane nests, we piled approximately 45 cm of bulrush, the primary material used by whooping cranes (Allen 1952), in a woven fashion to cover a 76 × 76-cm floating piece of oriented strand board secured with wire to two submerged stakes. In 2009, we found that black flies were attracted to whooping crane eggs; we, therefore, baited each artificial nest with one randomly assigned red-crowned crane or Siberian crane egg. The eggs were not incubated by adult cranes and were chilled before deployment. To protect the eggs from scavengers, we constructed exclosures (30 cm long × 15 cm wide × 20 cm high) consisting of a wooden frame (2.5 × 2.5 cm) covered with chicken wire. We obtained a high-resolution image of each baited nest and collected images for three subsequent days, from 14 to 17 April. Nest-visiting species of black flies began emerging from their breeding habitat on 9 April 2010. By 14 April, we had visited several nests and confirmed the presence of black flies. The performance of artificial nests was evaluated by comparing fly counts from high-resolution images with those from real nests.

Birds use uropygial gland secretions to keep their feathers clean and waterproof. They transfer the secretions by rubbing their head against the uropygial gland at the base of the tail and then rubbing the saturated head feathers against feathers on the rest of the body. Because uropygial gland secretions attract some species of black flies (Fallis and Smith 1964, Bennett et al. 1972), we measured their efficacy by comparing glueboard collections from unbaited decoys with those from decoys baited with real whooping crane wings. Decoys were deployed randomly on nests. The wings were stored in a freezer when not in use and transported to the nests in garbage bags on ice in a cooler. Fly counts from baited and unbaited decoys were compared using a paired t-test on logarithmically (n+1) transformed data (Muturi et al. 2007, Smallegange et al. 2010, Chen et al. 2011). All statistical analyses for all experiments were done with SAS 9.1 (SAS Institute Inc., Cary, NC, U.S.A.).


Diversity of black flies

We collected 13,471 larval and pupal black flies representing 21 species in seven genera (Table 1). The most abundant species, as immatures, on NNWR was Simulium tribulatum, which massed on the drop structures of the drainage ditches. Off the NNWR, the most abundant species were S. annulus and S. johannseni in the Yellow River, where densities on fallen leaves in the current were as high as 132 larvae per 2.5 cm2 (34.8% and 65.2%, respectively).

Table 1.  Numbers of adult black flies (Simuliidae) collected with carbon-dioxide traps and glueboards and from the contents of damaged or hatched eggs of whooping cranes (Grus americana), and of immature black flies collected from flowing water, on and near Necedah National Wildlife Refuge, Juneau County, Wisconsin, U.S.A., 2009–2011.
 Carbon-Dioxide TrapsGlueboardsEgg ContentsLarvae and Pupaea
  1. a= Numbers of larvae and pupae do not necessarily indicate relative abundance. b= 343 trap-nights in 2009, c= 117 trap-nights in 2011, d= based on 9 five-minute exposures, e= based on 16 five-minute exposures, f= from two eggs, g= from four eggs, h= possibly includes Simulium verecundum.

Cnephia dacotensis 1000001,817
Ectemnia taeniatifrons 16100000
Greniera denaria 17100001
Helodon gibsoni 00000051
Metacnephia saskatchewana 281500002
Prosimulium arvum 060000105
Prosimulium fuscum 00000067
Prosimulium mixtum 000000106
Prosimulium magnum 0100001
Simulium anatinum 132900000
Simulium annulus 46,2158701,0856691,2191,1361,360
Simulium aureum group4700001
Simulium congareenarum 0100000
Simulium croxtoni 0000006
Simulium decorum 573210000128
Simulium excisum 4400000
Simulium jenningsi 016000049
Simulium johannseni 233,5924,6508121,8106192,177
Simulium meridionale 34015,27200000
Simulium rostratum h 1,39311,03500003
Simulium rugglesi 46439000056
Simulium tribulatum 0200004,857
Simulium vandalicum 3000004
Simulium venustum 10,96940800001,423
Simulium vittatum 000000531
Stegopterna mutata 0120000726
TOTAL 293,23532,6701,0936813,0291,75513,471

We collected 325,905 adult black flies representing 21 species in seven genera. Two species, Cnephia dacotensis and Simulium vandalicum, were captured in 2009 but not in 2011. Despite lower trapping effort in 2011, we captured six unique species in carbon-dioxide traps: Prosimulium arvum, P. magnum, S. congareenarum, S. jenningsi, S. tribulatum, and Stegopterna mutata (Table 1).

We collected only two species, S. annulus and S. johannseni, at whooping crane nests during 37 nest visits. Simulium annulus was collected at nests as early as 11 April (2010) and as late as 25 May (2011) and was present at 72.9 % (n=27) of the nests. Simulium johannseni was collected at nests as early as 3 May (2009) and as late as 28 May (2011) and was present at 18.9 % (n=7) of the nests. Only S. annulus and S. johannseni were collected from the contents of damaged whooping crane eggs (Table 1).

During nest visits (n=37), we documented a total of 13,939 and 3,370 individuals of S. annulus and S. johannseni, respectively. When we had a high-resolution image available to make an estimate of black flies at a nest, the glueboard samples accounted for 43.2±10.8 % of S. annulus (range 0–100%; n=14) and 2.6±1.6 % of S. johannseni (range 0.2–7.1%; n=4) counts. We collected eight damaged or hatched eggs during seven nest visits. The average numbers of drowned black flies recovered from egg contents were 452.8±96.7 and 289.8±219.4 for S. annulus (range 10–883; n = 8) and S. johannseni (range 0–1,810; n = 8), respectively. We collected eggs with drowned S. annulus on three occasions and with S. johannseni on one occasion when we also collected glueboard and high-resolution samples at the same nests. In these instances, drowned specimens accounted for 49.4±19.3 % of the counts at nests (range 12.7–99.1 %) for S. annulus and 96.9±0.01 for S. johannseni.

The maximum number of S. annulus in a carbon-dioxide trap in one day was 20,574 (30 April 2009) and of S. johannseni, 68,022 (19 May 2009). The number of individuals and proportions of species varied markedly among traps. On 30 April 2009, for example, one of seven traps captured 442 females of S. annulus and 2,838 of S. johannseni, while another trap on the same day captured the reverse: 3,429 of S. annulus and 422 of S. johannseni. On the day of greatest total trap catch (19 May 2009), one trap captured 68,022 females of S. johannseni, while another trap captured only 75 females of this species.

Evaluation of carbon-dioxide traps for describing black fly variability at whooping crane nests

Time series correlations between counts at nests and from carbon-dioxide traps (nearest and all traps combined) were positive, indicating similar detections for seasonal patterns of S. annulus and S. johannseni (Figure 2). For both species, the correlations between fly counts from carbon-dioxide traps and whooping crane nests were weak, ranging from rs= 0.20 (nearest trap) to 0.56 (all seven traps) for S. johannseni (n=5) and from rs= 0.02 (nearest trap) to 0.21 (all seven traps) for S. annulus (n=21).

Figure 2.

Seasonal periodicity of Simulium annulus and Simulium johannseni at whooping crane nests and in carbon-dioxide traps on Necedah National Wildlife Refuge, Juneau County, WI, U.S.A., 2009–2011.

Among the nest visits with corresponding collections from carbon-dioxide traps (n=24), S. annulus had positive nest results (presence) 83.3 % of the time. The combined carbon-dioxide traps resulted in no negative values (absences) for those days, while the nearest trap provided one (5.0 %) negative result. On days that S. annulus was not detected at whooping crane nests (n=4), both the combined and nearest carbon-dioxide traps produced three (75.0 %) positive results. On days when we collected at least one S. johannseni during a nest visit and when corresponding carbon-dioxide trap results were available (n=5), the combined traps produced no negative results, while the nearest trap produced one (20.0 %) negative value. On days when we did not detect S. johannseni at nests (n=20), the traps provided positive (presence) values for the combined traps (55.0 %) and nearest traps (30.0 %).

In paired experiments (paired by day), the carbon-dioxide traps (all results combined) produced significantly fewer (t = 3.454, df = 11, P = 0.004) numbers of S. annulus than did whooping crane nests, but they did not produce significantly different (t = 1.913, df = 3, P = 0.151) numbers of S. johannseni (Figure 3). Whooping crane nests produced significantly higher (t = 2.516, df = 11, P = 0.029) numbers of S. annulus, but not of S. johannseni (t = 0.924, df = 3, P = 0.424), than did the nearest carbon-dioxide trap.

Figure 3.

Black fly counts at whooping crane (Grus americana) nests minus counts from carbon-dioxide traps. Data represent the log10 transformed number of black flies (Simulium annulus and Simulium johannseni) trapped during 2009 and 2011 on or near Necedah National Wildlife Refuge, Juneau County, Wisconsin, U.S.A. Symbols represent means and error bars represent standard errors. *Indicates probability that the mean differed from 0 (P < 0.05).

Evaluation of artificial nests

The nine artificial nests with eggs of red-crowned and Siberian cranes attracted no black flies. In the days leading up to deployment of the artificial nests on 14 April 2010, we recorded black flies at real whooping crane nests, including S. annulus at one nest on 11 April (891 flies) and at two nests on 12 April (389 and 729 flies).

Evaluation of uropygial gland secretions

Glueboards on whooping crane decoys, with and without real wings, captured only S. annulus. The mean number of flies caught on decoys without real wings (78.3±26.0) did not differ significantly (t = 1.271, df = 8, P = 0.240) from the number caught on decoys with real wings (102.1±28.0). The maximum number of flies caught on the glueboards was 205 and 234 for decoys without and with real wings, respectively.


Our results are consistent with previous studies (Shipp 1985, Anderson and Yee 1995) demonstrating that carbon-dioxide traps can be used to capture large numbers of black flies and that simuliid diversity on the landscape can be measured with ample trapping effort. The capture of six unique species in 2011, with only 34 % of the trapping effort of 2009, illustrates the periodicity of fluctuations in black fly populations and the value of less frequent sampling over a longer period of time.

Our sampling revealed 26 species of black flies in eight genera, including one species (Metacnephia saskatchewana) recorded for the first time from the United States and three species (Greniera denaria, Simulium congareenarum, and Simulium excisum) recorded for the first time from the state of Wisconsin. Collections of adults and of immatures included five unique species each. Unique collections of adults or of larvae and pupae represented species that do not feed on blood (H. gibsoni), occupy small easily overlooked breeding habitats (e.g., S. excisum), and possibly disperse from distances greater than 10 km (E. taeniatifrons). Our failure to locate the immature stages of S. meridionale, the third most abundant species in carbon-dioxide traps, might reflect breeding sites beyond 10 km or hatching at surveyed sites after we made our last larval and pupal collection (6 May). Females of S. meridionale can disperse at least 30 km from their natal sites (Fredeen 1956).

We found only two species of black flies, S. annulus and S. johannseni, that were attracted to nesting whooping cranes. Simulium annulus (formerly S. euryadminiculum; Adler et al. 2004) previously was thought to feed only on the common loon (Fallis and Smith 1964) until molecular analyses of blood meals revealed that it also feeds on the common crane (Grus grus) in Sweden (Malmqvist et al. 2004). Simulium johannseni has been recorded feeding on gallinaceous birds in our study area (Anderson and DeFoliart 1961).

Carbon-dioxide traps in our study poorly explained the variability in the presence/absence of S. johannseni at whooping crane nests. They performed better in explaining the presence, but not absence (false positives), of S. annulus at nests. When black flies were present at nests, their numbers in carbon-dioxide traps poorly explained the variability in numbers at nests and in the periodicity of the fluctuations. Carbon-dioxide traps in previous studies have accurately reflected the presence and relative abundance of most, but not all, species of black flies attacking horses (Equus ferus caballus) (Anderson and Yee 1995), and reflected the presence of mosquito species but not their biting rates on horses (Gerry et al. 2008). Carbon-dioxide traps have poorly reflected mosquito landing rates on humans (Kröckel et al. 2006). Discrepancies between numbers of black flies in traps and on hosts have been related to host defenses, such as ear flicking by horses (Anderson and Yee 1995). The discrepancies between the numbers of black flies in carbon-dioxide traps vs those at whooping crane nests might be explained by microhabitat differences between the locations of the traps and the hosts or by the host-seeking strategies and preferences of S. annulus and S. johannseni. Other than carbon dioxide, few sensory cues are shared by the traps and cranes; the traps, for example, are roughly a third the length of the body of a whooping crane.

Carbon dioxide alone is putatively a poor attractant for S. annulus, which uses additional cues to locate hosts (Fallis and Smith 1964, Bennett et al. 1972), possibly explaining the discrepancy between numbers at carbon-dioxide traps and crane nests. Host-locating cues used by S. johannseni are not well known (Adler et al. 2004). Our findings might reflect greater representation of S. johannseni on the landscape (counts from carbon-dioxide traps) or that whooping cranes are not a preferred host (counts at nests). In contrast, S. annulus is more host-specific (Adler et al. 2004), and its abundance at whooping crane nests, therefore, might be disproportionately higher than it is on the landscape.

If S. annulus is attracted to uropygial secretions of whooping cranes, we failed to detect it. Similarly, nest boxes baited with uropygial secretions of blue tits (Cyanistes caeruleus) and carbon dioxide traps baited with uropygial secretions of feral pigeons (Columbia livia) did not increase black fly numbers over controls in Spain (Martinez-de la Puente et al. 2011). However, uropygial secretions of common loons are powerful attractants for S. annulus (Fallis and Smith 1964), although the oils do not evoke a landing response (Smith3). One potential explanation for the discrepancy in results is the whooping crane wings we used had been stored in a freezer for approximately two years prior to our experiment. However, Lowther and Wood (1964) found that uropygial oils on a common loon skin still attracted S. annulus (as S. euryadminiculum) after it had been washed in cold water and detergent, degreased with a hydrocarbon solvent, prepared as a museum skin, and stored for more than three weeks in paradichlorobenzene before exposure to the flies.

To our knowledge, the attraction of black flies to eggs, especially those that are broken or have hatched recently, has not been reported for any species. If the attraction to eggs is based on chemical cues, isolation of the chemicals might prove beneficial in future surveillance programs. However, this attraction did not hold during our artificial nest experiment. Although we used real crane eggs in the artificial nests, they had been chilled prior to use and had not been incubated. Long-range cues, such as an actual bird or a decoy also were absent.

During subsequent visits to the whooping crane nests, we collected four females of S. meridionale on glueboards. Given that other bird species were present on the old nests at the time of collection and that several days to weeks had passed since whooping cranes used the nests, we cannot say with certainty that this species is attracted to whooping cranes in Wisconsin. However, S. meridionale has a wide host range (Adler et al. 2004), and we have identified S. meridionale collected by S. Zimorski from a whooping crane in Vermillion Parish, Louisiana, on 6 May 2011, indicating that the topic warrants further study.

Conclusions for conservation

Carbon-dioxide traps performed well for describing the black fly community in and around NNWR, but performed poorly for describing black fly presence/absence, population levels, and seasonal periodicity at whooping crane nests. Carbon-dioxide traps, therefore, could prove useful for general inventories of bloodfeeding flies but they may have limited utility for describing populations at whooping crane nests. Glueboards provide a direct measure of the density and proportions of host-seeking adults at the point of interest, which is essential for assessing the effects of black flies, including the risk of transmitting disease agents (Ritchie et al. 2003, Kröckel et al. 2006). The host-seeking cues and host preferences of S. annulus and S. johannseni necessitate the use of glueboards or other methods that directly measure populations at whooping crane nests to understand the influence of these flies on nesting birds.


  • 3

    Smith, S.M. 1966. Observations on some mechanisms of host finding and host selection in Simuliidae and Tabanidae (Diptera). M.S. thesis. McMaster University, Hamilton, Ontario, Canada. 144 pp.

  • 4

    Weinandt, M.L. 2006. Conservation implications of common loon (Gavia immer) parasites: black flies, haematozoans, and the role of mercury. M.S. thesis. Northern Michigan University, Marquette, MI. 51 pp.


We thank the U.S. Fish and Wildlife Service, the National Fish and Wildlife Foundation, and the Natural Resource Foundation of Wisconsin for funding this research. We are indebted to an outstanding field crew that included C. Bedwell, J. Boysen, J. Brennamen, M. Campbell, K. Gleason, T. Hunter, M. Jones, L. Maas, L. McKinney, C. Morris, J. Trutwin, E. Ulrey, and S. Zimorski. We thank S. Zimorski for sending S. meridionale that she collected from a whooping crane in Louisiana. R. Urbanek established the need for this project, and P. Gerard, J. Morse, D. Pfost, M. Pfost, D. Staller, and A.G. Wheeler kindly reviewed the manuscript. We thank the International Crane Foundation for the use of their Centers for Disease Control traps in 2011. This is Technical Contribution No. 5995 of the Clemson University Experiment Station, and is based on work supported, in part, by NIFA/USDA, under project number SC-1700276.