Fieldwork fun: Eristalis tenax and pollinator diversity

The field season is on in earnest now. Yesterday I was surveying blooming plant species at my field site, taking photos of the blooming plants as informal vouchers for now (vouchers = samples to prove that I correctly ID'd the plant, often collected specimens deposited at an herbarium in my field), and I managed to snap this awesome shot:

Eristalis tenax on Achillea millefolium

This guy is rather interesting, and not just because close-up shots of insects are cool by default.

I am pretty sure this is Eristalis tenax (a.k.a drone fly), and positive that it is a syrphid fly (a.k.a. hoverflies or bee flies). Syrphid flies are a group of flies which are bee or wasp mimics, meaning that they have characteristics resembling those of bees or wasps, which in theory is an antipredator adaptation conferring the advantages of the mimicked species against particular predators. E. tenax, our awesome, rather big (13-15mm wingspan [1]) syrphid fly is native to Eurasia [1] and was introduced to North America [1] before 1874 [1]. It is now widespread in North America [1,2].

The larval stage of this species is rather unappealing (called a rat-tailed maggot) and can pose problems particularly at agricultural sites, where they can become overabundant in ponds and livestock areas [3]. There have been cases of accidental ingestion of the eggs/larvae and subsequent myiasis (infestation by flies) of humans, causing unpleasant illness etc., but apparently the myiasis is treatable [3].

E. tenax is a pollinator, as adults feed on nectar [3] and so can be pollen vectors. indeed, although we tend to think of bees when we talk about pollinators, there are many other types of pollinator: flies, syrphid flies, butterflies, moths, skippers, wasps, birds, bats... There is even one documented case (research article) I am aware of where a lizard was demonstrated to be a pollinator!

I went digging around in the literature about E. tenax and found a study which compared the efficiency (transfer of pollen per visit) and effectiveness (number of visits per unit time) of E. tenax (and several other non-managed species) at pollination of Brassica rapa var. chinensis (pak choi) [link to open-access article]. The researchers conclude that E. tenax is equally effective and efficient as A. mellifera (European honeybee, a managed pollinator of considerable economic importance which is used extensively globally as a crop pollinator) on an individual basis as a pollinator, but due to much lower numbers of individuals in the populations of this and other alternative pollinators, A. mellifera remained the most important effective pollinator.

Just for fun, here's another syrphid fly I've photographed before. I think it's Toxomerus marginatus, but I'm not positive on the I.D. I am fairly sure it's at least in the genus Toxomerus, but I may be wrong about the species.

Toxomerus marginatus (?) on Rudbeckia hirta

The Root of Invasives: Burdock - Arctium lappa - Bardane

One visually arresting plant that you will be more likely to find in disturbed environments (eg parks, cities, agricultural areas, roadsides) is burdock. This plant is an introduced invasive plant originally native to Europe and Asia [1], and has been introduced, likely as a garden plant.

Arctium lappa whole plant view

Arctium lappa (greater burdock) is a particularly striking plant, rising to an impressive top height of 2.7m or even 3m [1,2]; its lower leaves can grow to enormous sizes, and its large purple flowerheads on tall stalks make the plant almost impossible to miss.

Arctium lappa inflorescence

A. lappa is broadly distributed in the US and Canada (US range map here, Canada range map here). Though introduced, it has no special status in the US [3], but is listed as a noxious weed in several provinces [4], including Alberta [5], British Columbia [6], and Manitoba [7]. This is likely because it can spread very aggressively in nitrogen-rich soils (eg agricultural areas) [1], because it can cause skin irritation and rash on contact [8], and the fine hairs on the seeds can be dangerous if inhaled [8], and because there is some evidence that the plant may be toxic to some mammals [9].

Arctium lappa inflorescence

This plant is very well known for its edible root. The root of A. lappa used to be fairly commonly consumed by humans from Europe to Asia but currently is only common in Asian cooking (especially Japanese) [1]. The root is edible, best harvested in the fall of the first year of growth (burdock is biennial) [1]. It is mild and crisp. The young leaves and shoots are also edible, generally cooked as a pot herb or in salads [1,10].

A. lappa is a frequent staple of traditional Chinese medicine [1], but there is currently insufficient evidence for its use to treat a broad assortment of ailments [11]. Its use is specifically contraindicated for diabetics and pregnant women [10].

Arctium lappa inflorescence covered with bees

A. lappa seems to be quite popular with Bombus spp (various bumblebee species), as it was actually a challenge to get photos of it without bees.

How Does a Plant Qualify for Noxious Weed Classification? Hoary Alyssum, Berteroa incana

Our star of the day is Berteroa incana (hoary alyssum, berteroa blanche), an introduced invasive species here in North America which is originally native to Eurasia [1]; it is a member of the Brassicaceae (mustard family). US range map here, Canada range map here. This plant is marked as weedy/invasive in the US [2], but is not listed federally as a weed in Canada [3]. Berteroa incana has noxious weed status in Michigan [2], and in Alberta, British Columbia, and Saskatchewan [3].

Berteroa incana inflorescence

I've mentioned a couple of other plants with noxious weed status on this blog: Leucanthemum vulgare, and Alliaria petiolata. So at this point you may be wondering what a plant has to do/be in order to obtain the noxious weed classification.

The answer to this question isn't always entirely straightforward, because there are a number of potential reasons for governments to confer noxious weed status on a plant, and because sometimes plants which exhibit similar traits to legally recognized noxious weeds aren't on the list for a variety of reasons (eg lack of resources, petition for review hasn't been tabled before the assessing body, insufficient scientific data, management concerns, political reasons, economic reasons).

Berteroa incana whole-plant view (in among a rambling pile of other plants)

The nice thing about Berteroa incana for the purposes of this discussion is that it exhibits more than one of the common traits that will lead a plant to be classified as a noxious weed. For example, it used to hold the noxious weed classification in Michigan [4], because it had been implicated in loss of pollinator diversity and therefore constituted a presence disruptive and deleterious to native ecosystem function [5]. It is unclear from my research whether this hypothesis has been disproved or if the plant has since been removed from Minnesota's noxious weed list for other reasons.

This plant's noxious weed status in Michigan must be attributable to agricultural or environmental undesirability, as these are the criteria listed by the state for plants to qualify for the noxious weed list [6]. It is possible that Berteroa incana was assessed as both; the list provides no further detail.

Berteroa incana inflorescence

Berteroa incana's noxious weed status in Alberta and British Columbia is explicitly outlined as being due to its toxicity to horses [7,8], and in British Columbia also because it interferes with alfalfa crop quality [8], by invading alfalfa fields and competing with the forage plant; it also ends up in the hay and is considerably less nutrient-rich than alfalfa, thereby reducing the nutritious value of the fodder produced.

Phyciodes cocyta collecting nectar from Berteroa incana (photo posted before on this post)

So a plant can end up on a noxious weed registry because it is particularly deleterious to ecosystem function, or because it is undesirable from an agricultural or environmental standpoint. If I have a reliable source on the matter, I will generally indicate why a particular plant is listed as a noxious weed. But if I don't, it is one of these reasons (and I couldn't find out which).

As for what to do about this plant... well, small populations can simply be pulled by hand [8], or in some places and contexts it may be appropriate to treat with an herbicide (2,4-D, dicamba, or glyphosate) [4,8].

I am remembering a visit I made to Toronto a few years back in August where I lost my voice because of the smog. The same thing is happening now with all this heat and traffic in Montreal, only it's not a visit; I'm stuck here until the end of the month and I'm losing my voice fast (I'm already at the stage where I can no longer hum). I had forgotten how hard it can be to breathe in a large city in summer...

A Well-Known Plant: Yarrow - Achillea millefolium - Herbe à dinde

The star of the day is one of the most broadly-distributed and -recognized wildflowers around: Achillea millefolium (common yarrow, also many other names).

Achillea millefolium inflorescence

This species (actually a huge complex of subspecies) is native more or less to the northern hemisphere's temperate zones, but particular subspecies are native to more restricted areas. This helps to understand the US range map of this plant, which lists the species as both native and introduced on most of the North American continent. This is because some subspecies are native, and others are introduced (particularly from Europe). The Canadian range map is considerably less detailed, going for the simple statement that the plant is native to all parts of Canada. This plant is listed as weedy/invasive in the US [1] but does not have weed status in any of the provinces or territories where such statuses are conferred [2].

Achillea millefolium whole plant

One of the main reasons for Achillea millefolium's fame is its array of purported and variously justified medicinal uses. This plant is a very popular herbal remedy [3,4] with a very long history of use in traditional medicine [3,4,5,6,7,8] for a wide variety of ailments. Modern analyses and tests have confirmed its efficacy as an anti-inflammatory at least in vitro [9], and there is some speculation (which I mention in my previous post about this plant) that the salicylic acid in the plant may make it an effective painkiller [3]. Other claims about the plant's medicinal value are currently insufficiently assessed to make a judgement on.

Achillea millefolium inflorescence lateral view

Regardless of its particular efficacy as a medicine, I do enjoy a cup of tea with the flowers or leaves of Achillea millefolium from time to time. The flavour, though strong, is pleasantly herbal. There is evidence that prolonged use can be potentially harmful and that it is possible to suffer allergic reactions to the plant [3,4], so I do not recommend that anybody consume it too frequently.

Achillea millefolium being pollinated by flies

Achillea millefolium is a hardy, drought-resistant [3,4,5,6,8,10] perennial with an extensive root system [3,4,5,6,8] that makes it suitable for habitat restoration in areas where erosion control is needed [6]. It is an obligate outcrosser [3,6], meaning that it must be pollinated with pollen from a different individual in order to produce seed. It is pollinated by insects [3,8], including beetles, flies, syrphid flies, wasps, and bees [6].

Oxeye Daisy - Leucanthemum vulgare - Margueritte

This is perhaps one of the most-recognized flowers around (though there are quite a lot of flowers that go by the common name 'daisy'). Leucanthemum vulgare is native to Europe & Asia [1,2,3] and was introduced to North America in the 1800s as an ornamental plant [2,3]. I have very briefly posted about this plant before.

Leucanthemum vulgare inflorescence

Since its introduction, Leucanthemum vulgare has spread over most of North America (US range map here, Canada range map here). Although it is pretty, this species is listed as an invasive species in the US [4], and classified as a noxious weed both federally and in most provinces where it is found in Canada [5]. In Canada, the noxious weed classification indicates that the plant is invasive and disruptive of native plants and ecosystems on a large scale. I do not recommend this plant to gardeners.

Clump of Leucanthemum vulgare

Some parts of this plant are edible [3,6]; I have eaten the young leaves before and they are rather spicy/carroty.

Leucanthemum vulgare inflorescence

This species is pollinated by bees, flies, beetles, wasps, and butterflies [2].

Crownvetch - Securigera varia - Coronille variée

Today we have yet another introduced species in the family Fabaceae (legume family), this time introduced not as a fodder crop or an ornamental, but for ecosystem management: Securigera varia (aka Coronilla varia, crownvetch) has been introduced to North America primarily as an erosion control plant [1,2,3,4,5,6]. Securigera varia is suitable for this purpose because it spreads rapidly (both through seeding and through vegetative propagation by root spreading) and forms a dense root system [1,2,3,5]. Like many members of the Fabaceae, Securigera varia is a nitrogen-fixing plant [2,4,5,6].

Securigera varia inflorescence

Since its introduction to North America in the 1950s, Securigera varia has spread across much of the continent (US range map here, Canada range map here). Unfortunately, those traits which make Securigera varia a suitable erosion control plant can also make it a problematic invasive plant [1,2,3,5,6]. This plant will tend to squeeze out other plants, disrupting ecosystem functioning [1,2,3,4,5,6].

Securigera varia foliage resembles that of Vicia cracca (cow vetch):

Securigera varia foliage

Bird's-Foot Trefoil - Lotus corniculatus - Pied de poule

Today, I continue in my recent theme of posting about Fabaceae (legumes) introduced to North America as forage plants (see: Galega orientalis (fodder galega), Medicago sativa (alfalfa), Trifolium pratense (red clover). This time, I'm going to talk about Lotus corniculatus (bird's-foot trefoil).

Lotus corniculatus inflorescence

This species is native to Europe, Asia, and Africa [1], and has been introduced to most of North America (US range map here, Canada range map here), primarily as fodder (livestock animal feed). It is a member of the family Fabaceae (legumes) and, like most members of this family, is both a good feed plant and a nitrogen-fixing plant [1,2,3] (nitrogen fixing: removes nitrogen from the atmosphere and puts it into the soil). This plant can become invasive and choke out native plants in some places, especially grasslands [1,2,4].

Dense patch of Lotus corniculatus

Unlike many Fabaceae used for fodder (including Medicago sativa and Galega orientalis), Lotus corniculatus doesn't cause bloat in cattle and so is a desirable fodder crop [1,2].

Lotus conriculatus inflorescence

This plant reproduces primarily through its roots [1], can occasionally self-pollinate [5], but is mostly pollinated by large bees [5], which must be strong enough to pull apart the flowers to access pollen and nectar [5]. Lotus corniculatus produces large amounts of nectar and so is a desirable honey crop [5].

Native Edibles : Flowering Raspberry - Rubus odoratus - Ronce odorante

Blooming right now are a number of the cane berries, a variety of species in the very large and economically important genus Rubus, which is in the family Rosaceae (rose family).

This genus has distinctive fruits which are aggregates (clusters that are kind of stuck together) of drupelets (fruit that consist of a fleshy layer surrounding a pit, which is composed of a shell exterior and a seed inside). This genus includes blackberries, raspberries, other cane fruit, and the star of the day: Rubus odoratus (flowering raspberry).

Rubus odoratus inflorescence

Rubus odoratus is native to North America, but has spread beyond its native range. Originally found in Ontario & Quebec [1], and in the eastern US [2], it is now also found in Nova Scotia and New Brunswick [1]. This species' conservation status is secure in its Canadian range [1], but it is endangered in Illinois and threatened in Tennessee [2].

I have posted about this plant before, but not in much detail.

Rubus odoratus broader view

Rubus odoratus has been introduced to Europe and is considered naturalized to several areas there now [3,4]. It success in areas outside of its native range is potentially attributable to some weedy characteristics, notably its seed set, which is large and composed of small, easily dispersed seed, and its rapid vegetative growth [5]. It was likely brought to areas outside of its range for its ornamental value [3]: it has large, attractive maple-like leaves and a long flowering period [3,6].

I cannot find much information about its pollination, but one usually reliable source indicates that this plant is of special value to pollinators (especially native bees), attracting large numbers of native bees, bumble bees, and honey bees, and that it provides shelter or nesting sites to some species of native bee [6].

Rubus odoratus visited by a Bombus sp. worker - note how full her pollen baskets are! She must have returned to the colony shortly after I took this shot to deliver her haul

I am in disagreement with several sources that state that the fruit of this plant is flavourless [5] or insipid [6]. I find the fruit tasty, if dry and a bit fuzzy on the tongue.

More Fabaceae: Red Clover - Trifolium pratense

So this week's posts have accidentally ended up with a unifying theme: I've been posting a lot about introduced species in the Fabaceae (legume family) brought to North America as feed crops. Primarily, I suppose, because a lot of the species in this family are just coming into bloom now, so I have a lot of them queued up for posting.

Trifolium pratense inflorescence

Trifolium pratense (red clover) is native to Europe [1,2,3] and is now found in most states, provinces, and territories in North America (US range map here, Canada range map here). This plant was originally brought to North America by settlers as a forage crop (food for grazing livestock) [1,2]. It is also, like many Fabaceae, a nitrogen-fixing plant [1,2].

Trifolium pratense inflorescence

This plant can frequently be found outside of farms, especially in disturbed fields, roadsides, parks, and unmown grassy areas [3].

Trifolium pratense general view

Trifolium pratense is edible and often used to make tea (I make herbal teas with it myself, it is sweet and tasty) [2], but because it is estrogenic [1,2] should not be consumed excessively by anyone with estrogen-sensitive conditions e.g. breast cancer [2] and is known to cause various health problems in livestock when improperly managed [4]. It has been touted as a treatment for a number of ailments but at present there is insufficient or conflicting evidence for most of these claims [5].

One rather pretty part of the plant that people rarely notice is the leafy casing that forms at stem junctions, and which looks rather like stained glass:

Trifolium pratense

The World's Favourite Forage Crop: Alfalfa, Medicago sativa

So I recently wrote about Galega orientalis, an introduced species that has been brought to North America as a forage crop (forage : in this case, referring to use for animal feed).

Medicago sativa

I have since discovered that there is Medicago sativa (alfalfa) in the forested side of the Notre-Dame-des-Neiges Cemetery. This plant has been introduced all over the world, including in most states and provinces (US range map here, Canada range map here). In the wild, this plant is a documented source of food for non-livestock animals [1], including antelope, deer, elk, Canada geese, and grouse [2]. Though this plant is widely distributed, it isn't listed as invasive. Note, however, that it is considered weedy in parts of the US [1,2], but is not included in weed lists for Canada [3].

Medicago sativa inflorescence

Medicago sativa, like G. orientalis, is a member of the Fabaceae (legume family), and like many members of this family it is a nitrogen-fixing plant [2,4,5].

Medicago sativa is considered the oldest forage plant [2,4], and is also the most widely used forage crop today [4,5]. It is so greatly favoured for the nutritional quality of the hay it produces and for its high yield by acreage [4,5].

Medicago sativa inflorescence

This plant can be used for grazing rather than haying (grazing : letting livestock feed from the plant directly in the field - haying : growing, cutting, and processing the plant for feed), but because in certain life stages it can cause bloat [2,4,5,6], grazing must be controlled with care.

Medicago sativa inflorescence

Although alfalfa (unsprouted seed) is often touted as a treatment for a variety of human ailments, there is insufficient evidence to support these claims [7], and some of the compounds found in alfalfa (unsprouted seed) are likely harmful to humans if consumed long-term [6,7].

Medicago sativa is primarily pollinated by a solitary bee in the Megachilidae (leafcutter bees), Megachile rotundata (alfalfa leafcutter bee), because pollination using Apis mellifera (honeybees) requires large numbers of naive (young) bees because they are not actually capable of obtaining the reward from this flower due to its shape, so they learn quickly to avoid it [5]. Although large numbers of naive bees are used to pollinate alfalfa in places, Megachile rotundata is increasingly preferred [5].

Introduced Species: Snails - Cepaea spp.

So I've noticed one thing about Montreal's fauna that's quite different from the upper Gatineau: extremely abundant relatively large snails. They are Cepaea hortensis (white-lipped snail) and Cepaea nemoralis (grove snail).

Cepaea hortensis - notice that the shell margin at the lip of the shell is pale

Both species are native to Europe and have been introduced in North America. I have found their abundance here in Montreal quite striking, as until coming here I had never seen snails of this size anywhere I had been in Quebec or Ontario.

Cepaea hortensis

Like most gastropods, this species are both hermaphrodites (but still have to mate with others to produce viable eggs). They are also among the species which produce a "love dart" -- essentially a sperm-filled spike that is shot into the body of another snail during mating. This dart actually does pierce the body of the other snail. Violent! ... Reproduction can be a very strange process indeed.

Distinguishing the two closely-related species without dissecting them is not 100% accurate -- while generally Cepaea hortensis has a white or yellow lip to its shell and Cepaea nemoralis has a brown lip, this isn't a perfect correspondence, so it is possible (but unlikely) that these individuals are misidentified.

Cepeaea nemoralis - notice that the shell margin at the lip (opening) is brown

Aside from the lip colour difference, both species show quite a lot of shell pattern polymorphism, varying in base shade from a pale creamy colour to a richer yellow, and having a variable number of brown stripes.

Introduced species: Silene spp.

One rather distinctive-looking species that many people are likely to come across, even in cities, is Silene vugaris (bladder campion). This introduced species is native to Europe and now distributed across Canada and the US (US range map here, Canadian range map here).

Silene vulgaris - male flowers

I have posted the above photo before (quite some time ago now), but I'm posting it again because it really does show clearly what it is that is visually attractive about this plant (also, I have since developed some basic image enhancement skills and can increase contrast and sharpen images to improve their informative value, so this version is a bit better), which was introduced in North America for its ornamental value [1].

Silene vulgaris - whole plant

This plant is not known to prosper in wild native environments but is reasonably common in modified habitats [1]. It is listed as a noxious weed in both the US [2] and Canada [3].

Silene vulgaris - foliage

S. vulgaris has some interesting reproductive characteristics; it appears in many forms; the flowers can be male (such as the ones pictured in the first image, which only have stamens), others are female, eg the one below with only pistils, and some are hermaphrodites with both male and female parts and function (I don't have any photos of a hermaphrodite flower) [4].

Silene vulgaris - female flower

Another plant from this genus which is also introduced is Silene latifolia (white campion). It is also widely introduced in North America (US range map here, Canadian range map here). Like its close relative S. vulgaris, S. latifolia is listed as a noxious weed in both the US [5] and Canada [6].

Silene latifolia - whole plant

The foliage of S. latifolia resembles S. vulgaris, but is generally broader and larger.

Silene latifolia - flower - note the comparative lack of detail/subtlety in the veination of the bulbous section

Flowers in this species are unisexual (either male or female) [7]. All of the S. latifolia flowers pictured here are female.

Silene latifolia

Introduced Species: Greater Celandine - Chelidonium majus - Grande éclaire

At the moment if you take a walk into the wooded portion of the Notre-Dame-des-Neiges Cemetery, you will see an abundantly growing, attractive yellow flower in much of the forest understory.

You might be tempted to conclude that it is the native Stylophorum diphyllum (wood poppy), which has similar leaves and flower. You would unfortunately be incorrect. This is actually the introduced species Chelidonium majus (greater celandine), which resembles Stylophorum diphyllum primarily because they are both members of the family Papaveraceae (poppy family). The native variety, however, has much larger flowers, its leaves are more deeply incurved, and its seed pods are round and hairy rather than the long and slender ones we see in this species.

Chelidonium majus population in bloom

This species is a member of the Papaveraceae (poppy family), so produces the latex-filled sap that is characteristic of this family. Given that, if you're sensitive to such things I would not recommend walking through a population of these in shorts.

Chelidonium majus

So if it's introduced, where is it originally from? Well, this species is native, as many of our introduce species, to Europe [1]. It is now distributed quite broadly across the US (range map here) and Canada (range map here). This species is considered invasive in some parts of the US [2] and is notably good at spreading and naturalizing [3].

Chelidonium majus seed pods

If you are having difficulty determining whether the plant you're looking at is Chelidonium majus or Stylophorum diphyllum, just look for the seed pods, which are very different in the two species. Above I have included a photo of the elongated seed pod of Chelidonium majus.

So why was it introduced here? This plant was originally brought over for medicinal purposes, used for a whole range of illnesses and problems including stomach ailments, warts, and menstrual problems [4]. Note, however, that there is not much evidence for its use in these capacities: it is possibly effective (some limited evidence) for stomach upset, and there is insufficient evidence for the remaining claims [4].