Category Archives: author – McIlveen

Snow Fleas

Figure 1. Diagram of a Snow Flea
Figure 1. Diagram of a Snow Flea

Late in winter almost every year if one is out and about in the woods, we will encounter an interesting group of tiny organisms on the surface of the snow. These are Snow Fleas (Hypogastrura nivicola). Snow Fleas, a species of Springtail, are very small insect-like creatures that are totally unrelated to true fleas that prey on dogs, cats, humans and other mammals. In fact they are no longer even considered to be insects. At one time, the group called Collembola were considered to be a primitive type of insect. Now, due to recent studies, they, along with two other groups, the Protura and the Diplura (two-pronged bristletails), have each been moved to their own Class equal in status to the insects. Collectively, these four groups make up the Subclass Hexapoda or ‘six-legged’ arthropods.

There are many species of Collembola. They are quite small, about one millimetre in length and most live in the soil where they are seldom encountered, at least knowingly by humans. They can be extremely numerous with populations reaching 250,000,00 per acre. They mostly feed on organic detritus, breaking down leaf litter and the like and aiding in the recycling of nutrients for plants.

Figure 2. Masses of Snow Fleas floating on water, Acton, April 30, 2013
Figure 2. Masses of Snow Fleas floating on water, Acton, April 30, 2013

The Snow Fleas represent the one Collembolan species that we do see fairly often. They appear in large numbers, and because their dark colour contrasts with the white snow surface, we take note. They tend to aggregate in small depressions such as old footprints in the snow. The depressions likely offer a microhabitat that is just a little warmer, is protected from the wind, and the snow is likely to be saturated with liquid water. In any case, the Snow Fleas appear in large numbers and look much like dust particles. If one looks closely, you can see them jumping about on the surface of the snow.

Figure 3. Close-up of Snow Fleas in Figure 2
Figure 3. Close-up of Snow Fleas in Figure 2

These photos were taken on April 30, 2013 at a small vernal pool along the Guelph Hiking Trail south of Acton. The masses of Springtails floating on the water looked a lot like globs of oil. It is uncertain if these animals were at the end of their days or if they had trouble breaking free from the surface tension of the water. Some of them were certainly still alive and were jumping about. Nevertheless, the photographs give some idea of the abundance of the creatures.

Although they have legs to help them move about, Springtails are also equipped with an unusual abdominal appendage called the furcula. This structure is what gives the group its name. It folds beneath the body with the loose end tucked into a receptacle also under the body. The furcula is held under tension and when needed, the tension reaches a level that the end slips out of the receptacle. The furcula snaps against the substrate and this throws the Springtail into the air to escape.

Snow Fleas are able to live quite comfortably in the snow and survive low temperatures owing to a special glycine-rich protein that acts as a form of antifreeze. In addition to the important role in recycling nutrients noted above, Springtails have been reported to provide a valuable ecological service by moving spores of mycorrhizal fungi and destroying spores of plant pathogens. Certain species have been blamed for damaging alfalfa crops. They have also been put to use as indicators of soil contamination owing to their sensitivity to certain chemicals in the soil.

by W.D. McIlveen
Halton/North Peel Naturalist Club

Results of the 2012 Christmas Bird Count

The 22nd annual Christmas Bird Count took place on December 27, 2012. The fresh fall of snow overnight hindered or even prevented the participation of some count volunteers. Overall, there were 18 participants that took part in the field observations.

Generally, the Count produced close to average results based on comparisons with previous counts. The total number of species reported was 51 and the total number of birds was 10,082. The long-term averages for those are 49.9 and 9760 respectively. The results for the individual species are presented in the attached table. A new species for the Count was Cackling Goose seen in Count Week at Fairy Lake in Acton (See report in this issue of the newsletter). Also not previously reported was a Scaup sp. but this may not be entirely new as Lesser Scaup was recorded in 2011. New high counts were reported for Cooper’s Hawk (6), Merlin (2), Hairy Woodpecker (29), Bohemian Waxwing (180) , Dark-eyed Junco (693), and Northern Cardinal (101). Higher than average numbers of Canada Goose (3755), Mallard (682), Cedar Waxwing (159), American Tree Sparrow (591), and American Goldfinch (269) were recorded. Seventeen species had lower than average numbers and this offset the higher numbers mentioned above.

Thanks to the following participants: Ray Blower, Mark Cranford, Betty Ann Goldstein, Megan Kenzie, Lou Marsh, Meryl Marsh, Irene McIlveen, W.D. McIlveen, Fiona Reid, Dawn Renfrew, Teresa Rigg, Don Scallen, Dan Shuurman, Rick Stroud, David Sukhiani, Janice Sukhiani, Patrick Tuck, and Dave Williams.

Many thanks once more to Larry May for arranging access to the Maple Lodge Farms property and to the Halton Regional Police Service for use of the community boardroom for the wrap-up session.

Cackling Geese at Fairy Lake, Acton

On December 23, 2012, Bradley Bloemendal posted the sighting of at least three Cackling Geese at Fairy Lake in Acton was on the ONTBirds hotline. Next day, I went to check out the report. At that time, there was still a fairly large area of open water on the lake. I counted 330 Canada Geese, 32 Mallards, one American Black Duck, 6 Common Mergansers, and 8 Ring-billed Gulls. I could not distinguish any Cackling Geese among the birds there but they could easily have been present among the geese lined up on the ice off to the west side of the lake. Many had their heads tucked in and size differences were impossible to determine under those conditions. On December 26, I went back and found that much of the formerly-open water had frozen. The Canada Goose count was now down to 130 and those were present in the last open water close to the point in Prospect Park. Among them were four Cackling Geese. As can be seen in the accompanying photo, the Cackling Geese are much smaller than the regular Canada Geese and their bills are stubbier. Their presence was therefore confirmed for Count Week for the Halton Hills Christmas Bird Census that took place on December 27, 2012.

The taxonomy of birds that most people would recognize as Canada Geese has been in debate for many years. Splitting into various races was mentioned by Tavener over 90 years ago. Over the years, the number of recognized races or sub-species has stood at ten to twelve different forms. Distinction between these is blurred at best but size is one of the main features. There is much overlap and intergrading between the races as well as hybridization, not to mention size differences caused by diets and food supply, and thus distinction in the field is nearly impossible. It was no surprise though that American Ornithologist’s Union’s Committee on Classification and Nomenclature decided to split Canada Goose (Branta canadensis) into two species: Canada Goose (B. canadensis) and Cackling Goose (Branta hutchinsii). This became official in 2004 in the 45th supplement to the Check-list of North American Birds. Greater Canada Goose contains six subspecies, namely canadensis [Atlantic], interior [Interior], maxima [Giant], moffitti [Moffit’s], parvipes, fulva [Vancouver], and occidentalis [Dusky]. The smaller Cackling Goose (Branta hutchinsii) group includes the subspecies hutchinsii [Richardson’s], [Bering], leucopareia [Aleutian], taverneri [Taverner’s], and minima. The asiatica are already extinct.

Cackling Geese
Cackling Geese

The Cackling Goose was first recognized as a separate species when Sir John Richardson collected a specimen in 1822 north of Hudson’s Bay. He named it Branta hutchinsii after a man by the name of Hutchins who was employed by the Hudson Bay Company. For this reason, it is sometimes referred to as Hutchins’s Goose but now it is identified as the Richardson’s subspecies of Cackling Goose. The geese at Fairy Lake appear to be of this subspecies as their breasts are light coloured, unlike the Cackling Cackling Goose (minima) which usually has a much darker breast.

Nomenclature of Canada and Cackling Geese is far from settled and we can expect further changes. There has even been a recent proposal that the group be divided into six species with 200 subspecies. This classification would be quite unworkable for field biologists even though DNA analysis might justifiably distinguish that many true species. It is simply not feasible to recognize that number of subspecies without access to DNA laboratory testing. We are only now just learning to separate out the Cackling Geese. Let’s not go too far in the taxonomic splitting exercise. There is always a possibility that while there may be genuinely different genetic groups, the differences may not be enough to separate the species and in the end, we might still be looking at one large but diverse species of Canada Goose.

by W.D. McIlveen
Halton/North Peel Naturalist Club

Dust devils

Earlier this Spring on two successive days, I was driving along our gravel road and noticed a ‘dust devil’ at the same location each time. I am sure that everyone has seen such things at some point in their lives. Seeing one is not at all unusual but noting two in the manner that they occurred prompted me to prepare this little note.

The conditions that must exist to form the dust devils will likely occur many times but they remain invisible. We only see them when they cause fine dust, leaves, paper and similar light materials, rarely snow, to be swept up into a circular funnel. Without the telltale visual evidence, we pay no attention for we simply cannot detect them. Similarly, we seldom have the opportunity to photograph them. They typically only last a few seconds so unless we have a camera already at hand, we don’t get a fair chance to document their existence.

Dust devil photographed at Lake Bogoria, Kenya, 2001 (Photo by W.D. McIlveen)
Dust devil photographed at Lake Bogoria, Kenya, 2001 (Photo by W.D. McIlveen)

In many respects, they are like miniature tornados with a spinning vortex. ‘Whirlwind’ is a fairly good description. They may be as small as meter wide and ten meters high to rare ones that might be ten times as wide and one hundred times as tall. The motion is nearly always upwards in the form of a swirling updraft under sunny conditions during fair weather. A basic requirement is that there are areas with a differential in heating of different air pockets. The devils form when hot air near the ground surface rises quickly through a small pocket of overlying cooler, low- pressure air. Under the right conditions, the air may begin to rotate. As the air rapidly rises, the column of hot air is stretched vertically, causing intensification of the spinning effect. A fully-formed dust devil is a funnel-like chimney through which hot air moves, both upwards and in a circle. Additional hot air rushes in toward the developing vortex to replace the air that is rising As the hot air rises, it cools, loses its buoyancy and eventually ceases to rise. As it rises, it displaces air which descends outside the core of the vortex. The spinning motion cause the dust devil to move forward. The upward speed of the air within the vortex has been reported to be at least 40 km/hr. On occasion, wind speed in the rotating air can reach as high as 120 km/hr.

Dust devils are most evident in flat terrain that lacks vegetation, or in fields, deserts, or tarmac. Such conditions favor the build-up of heat near the ground surface as well as the increase the chance that dust or sand may be swept up. Clear, or relatively clear, skies enable solar energy to easily reach the ground to warm the surface yet have cooler air above. Ambient wind needs to be very low or absent or else there would be too much mixing of the cooler upper air with the heated air at ground level. If two distinctly different air temperature regimes cannot be established, then a dust devil cannot form.

Somewhat similar vortices form in the center of large fires like forest fires where there is a rather obvious source of heated air and smoke. Vortices also occur in the lea of buildings that are exposed to winds, depending upon the size and shape of building and other characteristics of the surrounding environment. The latter are notably different in origin, arising from mostly lateral winds. The swirling motion can cause snow to form drifts and other debris to form circular piles on the downwind side of the structures. These materials fall to the ground in the centre of the vortex which lacks the air speed to keep the materials suspended.

Dust devils seldom cause significant damage or injury, simply because they are limited in size and do not last. On occasion, they might do limited damage if the particular conditions allow the wind speed to be unusually high. The wind movement could potentially move materials from one place to another and this may be undesirable from a human perspective. Dust might become entrained in the wind and this might be quite undesirable. They could cause the components of the dust or creatures nearthe ground surface (e.g. insects, plant pathogens, weed seeds) to become airborne and moved to new locations. Occasionally small rodents could be forcibly moved from one place to another. In general though, dust devils are mostly just fleeting visible indicators of the fact that our physical environment is constantly in flux.

by W.D. McIlveen
Halton/North Peel Naturalist Club

Weather-related Stress on Plants, 2012

So far, the year 2012 has seen some disruptions in normal weather patterns. In March, we experienced some rather warm days that caused many wild flowers to appear early, foliage on trees and shrubs to emerge early, and for amphibians to start breeding early as well. This was followed by a relatively cool April. Then in June and July there were days with high temperatures and dry conditions. This report examines some of the impacts of those weather conditions on plants.

Temperature and water availability are two of the most important environmental factors that control the welfare of plants. When these are present at high or low values, then we can expect that certain stresses will start to occur or that the plants will perform at less than optimum growth rates. Not all plants will respond in exactly the same way for some are adapted for low temperatures while others prefer warmer temperatures for example.

The conditions that prevailed in the spring 2012 had major consequences for some crops, notably the McIntosh cultivar of apples. Specifically this was because of a frost or low temperature event at a critical time in flowering. As a consequence, the pollination rate was extremely low and little fruit was set. Other cultivars fared somewhat better. It is uncertain whether weather (i.e. frost) was the main factor but it was rather obvious that wild fruit loads on trees and shrubs through Northeastern Ontario were extremely poor and mostly zero by late this summer. A conversation with a wild blueberry seller confirmed that the blueberry harvest was extremely poor and pickers had a very difficult time finding enough fruit to collect and sell. Aside from the very high prices that could be commanded for the limited fruit that was available, it is easy to appreciate that wildlife such as birds and bears will have a difficult time finding food this year.

Figure 1. Ice and cold temperature injury to Alternate-leaved Dogwood, Acton, May 2, 2012
Figure 1. Ice and cold temperature injury to Alternate-leaved Dogwood, Acton, May 2, 2012

Locally, the effect of low temperatures in the early growing season did not appear to have significant impacts for native plants. Most native plants do retain some tolerance to short periods of low temperatures. Even at this, the young foliage on Alternate-leaved Dogwood showed a reddish-brown discoloration along the margins and between the veins. Reddish coloration often accompanies a physiological phosphorous deficiency that is induced by cold temperatures. This gradually disappeared as the growing season advanced. There was a small amount of acute necrosis of some Dogwood leaves but this only occurred where ice formed when rain runoff from the house roof froze on the foliage (Figure1).

Weather-stress conditions occurred later in the growing season in the form of drought. It was reported that the timing of the drought was particularly bad for corn producers. Although corn plants were widely seen to be suffering (leaves rolled up) in many parts of the Province, the plants remained alive for a long time. The yield though was impacted since the silks could not be pollinated during the critical short window when silks and pollen must come together. The overall effect was a low rate of pollination and this in turn will impact upon the amount of seed that gets set. The true impact can only be known after the harvest has been completed. It is expected that the price for corn for animal and human food will be quite high due to shortages in the crop through much of the corn-producing parts of North America.

Figure 2. Total monthly precipitation reported at Pearson Airport from March through July, 2012.
Figure 2. Total monthly precipitation reported at Pearson Airport from March through July, 2012.
Figure 3. Monthly precipitation reported at Pearson Airport from March through July, 2012 excluding the rain events on June 1 and July 31
Figure 3. Monthly precipitation reported at Pearson Airport from March through July, 2012 excluding the rain events on June 1 and July 31

The reported monthly totals of precipitation for the study period (March through July) may be a somewhat misleading. As shown in Figure 2, the monthly totals at Pearson Airport for March, April and May are not much more than half of the normal amounts for each month. The amount for June is very close to average while that for July is about 30% above average. But timing is everything. Of the total of the 76.4 mm for June, nearly half (37.4 mm) fell on the very first day of the month. In July, the largest rainfall that measured (38.8 mm) fell in a thunderstorm on the very last day of the month. There were a couple of light rains on July 22 and July 25 but these were not even seen in many parts of our area. This means that there was an extended time (over seven weeks from June 2 to July 21) where practically no rain fell at all. In combination with some days with rather high temperatures, most plants without an irrigation source would have been subjected to some very severe drought stress. Figure 3 shows the same data as Figure 2 but the amounts of rain that fell on June 1 and after July 22 have been excluded to provide a more realistic image of the conditions that plants would have experienced. Some native plants in our area did exhibit symptoms of weather (drought) stress. Such symptoms included drooping of the foliage and later, complete drying of the foliage. (Figs. 4 and 5).

The normal growth of plants includes uptake of water from the soil and transpiration of that water through the foliage. When there is an inadequate supply of water, the plant has several responses to help cope with the shortage. A prime reaction is to close the stomates to reduce the loss of water through the leaves. While water loss may be reduced by this action, it also reduces the amount of nutrients that can be absorbed from the soil and transported to the leaves. Closure of the stomates reduces the amount of carbon dioxide that can be taken up to become involved in the photosynthetic process. Reducedtranspiration means that the foliage does not get cooled through evaporation of the water. As a result, the leaf temperatures get raised above optimum and so the plant cannot grow at an optimal rate. Overall though, it is most desirable to the plant to conserve the water it has, rather than grow large. To compensate for the lack of water, many plants will shed their excess foliage. This effectively cuts down on the total leaf surface that is transpiring at any given time.

Figure 4. Temporary wilting of foliage of Green-headed Coneflower due to drought
Figure 4. Temporary wilting of foliage of Green-headed Coneflower due to drought

Hormones produced in the roots trigger the mechanisms that lead to abscission of excess leaves, much like the normal fall of foliage each Autumn. Stressed trees for example might show a high proportion of yellowed foliage (often older leaves and leaves lower on the stem. Another clue to the drought stress is an excess of recently-fallen foliage on the ground much earlier than would normally take place. Sometimes, totally dried or dead foliage will be retained on the branches.

Figure 5. Foliar necrosis due to drought stress on Wild Raspberry, Acton, July 25, 2012
Figure 5. Foliar necrosis due to drought stress on Wild Raspberry, Acton, July 25, 2012

Late in August, large patches of totally brown, necrotic trees and shrubs were seen in the area south of Parry Sound. This area has rather shallow soil soil and therefore the water reserve in the soil is quite prone to drought stress but the degree of stress in the summer 2012 in that area is the most severe that the author has witnessed in over 35 years. Whether or not the affected vegetation was killed outright will become known in 2013; however, there is little doubt that there will at least be a notable impact on the affected sites for several years to come. Locally, the stress observed will not likely have an observable enduring impact on perennial species but cumulative stress from similar conditions in future years could produce notable effects, likely as smaller plants with less flowering, lower seed set, or greater incidence of insect and disease attacks.

by W.D. McIlveen
Halton/North Peel Naturalist Club

Pygmy Grasshoppers

Particularly in Spring, a walk in the woods might turn up a very tiny grasshopper among the dead leaves. These are likely Pygmy Grasshoppers, not ‘baby grasshoppers’. They are also known as ‘grouse locusts’ or ‘grouse grasshoppers’ or in one case, a ‘frog groundhopper’. Pygmy Grasshoppers are members of the suborder Tetrigodea and most occur in the Family Tetrigidae. One exception is Tettigidea lateralis that occurs in the closely-allied Family Batrachideidae. The seven species that are known to occur in our area are listed in the following table and samples are illustrated in the attached pages.

These grasshoppers, as their name implies, are quite tiny with adults ranging from about 7 mm to only 14 mm (half inch) in length. Females are slightly larger than males. Because of their small size and generally cryptic coloration, they are easily overlooked. They can be of various colours, browns though gray and mottled, but never green. Their eyes are rather pronounced and the pronotum is often elongated along the back to cover the thorax. The antennae are short and they lack auditory and stridulatory organs. Wings may be long or short.

Although they can tolerate slightly drier sites, most prefer to live on the ground in damp, muddy situations, frequently close to water. They are reported to feed on vegetation debris and microscopic algae that accounts for their preference for moist habitats. Eggs are laid in soil or mud. Because they over-winter as adults, they are likely to be active shortly after the snow melts in the spring. Given the mild winter this year that gives prospects for an early start to the season, we could expect to see these little fellows out and about in the very near future.

by W.D. McIlveen
Halton/North Peel Naturalist Club

Results of Monitoring Late-flowering Plants in Halton Hills, 2002-2011

The impact of climate on the biota of an area can be manifested in a number of ways. One possible effect of global warming and climate change in general is that the growing season could be extended. We can measure temperature changes easily enough but the effect of the temperature changes may not be immediately apparent. In part, this is because the changes will be gradual and small but changes are obscured by annual and daily variations. One means of assessing the long-term influence of climate changes is to follow the phenological changes in the flora. This could include such things as documenting the dates of first flowers (anthesis) or bud breaks of tree leaves. In the present investigation, we have chosen to record the dates when open or viable flowers are still present on plants in the area late into the season. This can be taken as one measure of a late growing season. It is not possible to know the exact date when an individual flower is no longer viable. In reality, the probability that the late-flowering blooms could be fertilized and go on to produce seed is rather low; however, the monitoring of such flowers over a period of time should provide a measure of the change in growing season dates.

Each autumn from 2002 until 2011, members of the Halton/North Peel Naturalist Club have conducted a survey of the plants still in flower in the latter part of November. The exact dates of the survey are indicated in Table 1. The dates ranged between November 14 and November 26. The exact locations of the survey have changed somewhat each year; however, the Willow Park Ecology Centre and the Lucy Maude Montgomery Garden in Norval have been checked every year. In the earlier years, the woods near the Georgetown Fair Grounds were examined while more recently the survey route included the Dominion Seed House Park. As well, incidental observations of flowering plants in parts of Georgetown have been added to the list.

Table 1. Survey dates and number of plant species in flower in Halton Hills, 2002-2011
Table 1. Survey dates and number of plant species in flower in Halton Hills, 2002-2011

Species observed still flowering on the survey dates are included in Table 2. The number of species in flower observed has fluctuated from year to year (Figure 1) but there is general trend to larger numbers over time. In part, the trend might have been influenced by the choice of sites visited; however, other factors such as site management at Willow Park and natural succession of species within an area likely played a mitigating role as well. Overall, the survey documented as few as 11 species still in bloom in 2003 and as high as 41 in 2009.

The vast majority of the 108 species on the list (Table 2) are cultivated garden species along with several species generally regarded as introduced weeds. The cultivated garden species includes several that are native species that have been purposely planted. Only about 10% of the species on the list are ones that are both native and endemic to the area. Only two species, Canada Goldenrod (Solidago canadensis) and Common Dandelion (Taraxacum officinale) were found flowering every year. Other commonly encountered species (6 to 8 years each) were Yellow Chamomile (Anthemis tinctoria), Calendula (Calendula officinalis), Garden Chrysanthemum (Chrysanthemum hybrid sp.), Wormseed Mustard (Erysimum chieranthoides), Scentless Chamomile (Matricaria perforata), Canker Rose (Rosa canina), Common Groundsel (Senecio vulgaris), Tall White Aster (Symphyotrichum lanceolatum), and New England Aster (Symphyotrichum novae- angliae). Interestingly, all of the species on the most common list except for the Wormseed Mustard and the rose are members of the composite family.

Figure 1. Number of plant species observed flowering in late November surveys in Halton Hills, 2002- 2011
Figure 1. Number of plant species observed flowering in late November surveys in Halton Hills, 2002- 2011

A survey of this type on its own cannot be expected to demonstrate that climate change is having a significant impact on the length of the growing season. In combination with many other surveys though, the data set will be more robust in demonstrating that a change is indeed occurring. This effort is a small contribution towards that end.

by W.D. McIlveen
Halton/North Peel Naturalist Club

Results of the 2011 Halton Hills Christmas Count

The 21st annual Christmas Bird Count for Halton Hills was held on December 27, 2011. The weather that day was marked by a fairly constant snowfall that restricted viewing of birds and generally made for a dull day with temperatures just above the freezing mark.

The results for the 2011 Count are summarized in the attached table. For comparison, the average and high numbers recorded for the previous 20 years are also included in the table. The total number of species recorded for the day plus Count Week was 56 and that is just below the maximum count of 57 species. The species count was bolstered by five new species including Northern Shoveller, Ring-necked Duck, Lesser Scaup, and Red- breasted Merganser observed at the Maple Lodge farms sewage lagoons. The Mute Swan was seen at an estate on the 10th Line near Terra Cotta but although it was counted here, caution needs to be exercised in case it is really a captive bird. With the new additions, the cumulative number of species for the Count Area rises to 101. Two species (Great Blue Heron and Easter Screech Owl) were found in Count Week and not on Count Day. The total number of birds (10777) is somewhat higher than the long-term average count of 9744. Considering the weather, the day has to be viewed as very successful.

New high numbers of Common Goldeneye (18) and American Robin (266) were encountered and this might be attributable to conditions prevailing during or slightly before the count period for 2011. New high numbers of Red-bellied Woodpecker (11) are likely due to increases in the local resident population for the species is known to be increasing substantially across Southern Ontario. Both Green-winged Teal and Bufflehead with two birds each increased from the previous high count of only one. Black-capped Chickadee matched the previous high of 465 birds. Other species were present in numbers within previously established ranges for the respective species.

In total, 23 people participated in the count, either as observers or as feeder watchers. Thanks to the following participants: Anna Baranova, Judy Biggar, Brad Bloemendal, Ray Blower, Mark Cranford, Betty Ann Goldstein, Charles Hildebrandt, Larry Martyn, Diane McCurdy, Irene McIlveen, W.D. McIlveen, Michael Pearson, Fiona Reid, Valerie Rosenfield, Don Scallen, Dan Shuurman, Chris Street, Rick Stroud, Janice Sukhiani, Jake Veerman, George Wilkes, Marg Wilkes, and Dave Williams.

Many thanks to Larry May for arranging access to the Maple Lodge Farms property and to Halton Regional Police for use of the community boardroom for the wrap-up session.

by W.D. McIlveen
Halton/North Peel Naturalist Club

Giant Swallowtails and Climate Change

Recently, one of the items covered by the news media was the change in distribution of various species owing to climate change. There are other causes for expansions of populations other than climate shifts but this discussion is limited to the global warming phenomenon. The media accounts included the recent appearance of fish species in the ocean much further north than where they normally occur. One species that was mentioned that has relevance to our own area was the Giant Swallowtail Butterfly.

Figure 1: Giant Swallowtail Butterfly adult, Prince Edward Point, May 30, 2009
Figure 1: Giant Swallowtail Butterfly adult, Prince Edward Point, May 30, 2009

While it is a good thing that the media covered this important story, they unfortunately got it wrong. To listen to what they were saying one was left with the impression the species involved were fleeing from excessive heat in their traditional areas and seeking respite in cooler areas. This is not the case. The geographic range expansion is possible only because the new areas are now offering conditions (slightly warmer) where the cooler conditions had prevented then from surviving before. Giant Swallowtails (Papilio cresphontes) are the largest butterfly in much of North America. Their wingspan ranges from 10 to 14 cm across! (Figure 1). They tend to stay in woodland areas or, in the southern US, in citrus groves. The adults sip flower nectar for food. The larvae of this butterfly are known as the ‘Orange Dog’, not for their colour but for their host in citrus groves. The caterpillars look a lot like bird droppings and can get as big as 4.5 cm long! (Figure 2)

They generally adopt a disguise by looking like bird droppings, an appearance that they retain until they pupate. Another deterrent to would-be predators is the osmeterium. This is a reddish, forked gland located behind the head that is extended when the caterpillar disturbed. The osmeterium exudes a fluid that is considered to smell terrible and deters any attacker.

Figure 2. Giant Swallowtail Butterfly larva on Common Hop-tree seedling, Windsor, September 6, 2011
Figure 2. Giant Swallowtail Butterfly larva on Common Hop-tree seedling, Windsor, September 6, 2011

In years past, Giant Swallowtails were essentially restricted to the far southern parts of the province. They would occasionally wander farther and one vagrant had been reported at Ottawa. Now they are much more frequent in parts of the province where they were seen only occasionally. How much of this recent range expansion is due to climate change is still unclear. Milder winters could certainly assist in the survival of the species over the coldest part of the year. A key limitation in their distribution is the availability of their host plants.

Hosts of the Giant Swallowtail all belong to the citrus plant family Rutaceae. We do not have many groves of oranges or lemons in Ontario to sustain the butterflies but we do have a few other members of the plant family. The list includes Gas Plant (Dictamnus albus), Cork Tree (Phellodendron amurense), Common Rue (Ruta graveolens), Common Hop-tree (Ptelea trifoliata) and American Prickly-ash (Zanthoxylum americanum). The first three mentioned are all introduced or non-native species. They are rarely grown and are thus hardly capable of sustaining populations of the butterflies in Ontario. The Hop-tree is rather uncommon in Ontario and restricted to the Carolinian zone. The main job of supporting the larvae of the Giant Swallowtails then falls to the Prickly-ash that has a much wider distribution than the others though it also tends to grow in more southern parts of the province. Prickly-ash is a relatively inconspicuous species that goes unnoticed unless one needs to cross through a patch of it. Then the thorns on its stems are more than adequate to grab the traveler’s attention. Other than vagrant butterflies that might be carried by the wind, the anticipated range of the butterflies is going to strongly mirror the distribution of Prickly-ash. Perhaps the changing climate will allow that plant to extend its range and thus allow the butterflies to follow further a field. It will be interesting to follow shifts in distribution patterns for these species as well as others that exhibit similar types of range restrictions.

by W.D. McIlveen
Halton/North Peel Naturalist Club