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

Wasps: Not Just Flying Agents of Pain

One of the things I encounter a lot when I talk to people about pollination is an intense fear of bees, and most especially of wasps. But wasps don't just sting you (and most won't sting without provocation); they also are pollinators. While on holiday at the lake, I captured a great series of a wasp worker hanging out on Achillea millefolium.

Unknown species of wasp on Achillea millefolium

Wasps are generally less hairy/fuzzy than bees, so they don't carry pollen as efficiently. But less efficient pollination != no pollination. Indeed, wasps are important pollinators in many ecosystems.

Another possible reason that wasps aren't such efficient pollinators of bees is that they don't (for the most part) rely solely on flowers for food. This individual actually may have inadvertently provided pollination services to the flower, but wasn't there collecting either nectar or pollen. She was dining on something else entirely:

A wasp eating something - note the ball of wax-yellow stuff

So I wondered what in the world she was eating. I looked from the front angle, hoping another angle might illuminate the matter:

Wasp eating something -- ball of stuff still unidentifiable

Nope, that was no help. Still a generally formless lump of gunk.

A quick glance around the environs, however, provided the answer:

Seems like a colour match for that wasp's meal

This dead grasshopper was on the stem of the flower where I found the wasp, and judging by the colour match and the big old hole in the dead grasshopper's abdomen, I suspect that the wasp found herself a rich source of protein and was taking advantage.

I suppose one animal's rather grisly find is another's feast.

Anyway, wasps will seek out other sources of protein (often to feed their young), including other insects, whereas bees generally don't. This reduced reliance on flowers may make them less likely to do the systematic flower-by-flower collection that also makes bees such suitable pollinators for flowers.

Wasps are actually an excellent biological control agent, as many of them have preferred prey which are pest insects on crops. I encourage them in my own garden because they're so efficient at getting rid of unwanted insects.

These oft-maligned insects are actually pretty awesome -- as long as you don't swat them or approach their nests late in the season.

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].

Yarrow - Achillea Millefolium - Herbe à Dinde

A. millefolium inflorescence

Cette plante est très commune dans la région. Elle est facile à identifier et préparée comme thé était utilisée part les aborigineaux pour réduire la fièvre et pour aider à dormir. Je met cette plante dans mes tisanes, mais elle a un goût très fort donc je conseille les gens de l'utiliser de manière restraint. Avant d'y goûter, on devrait s'assurer qu'on n'a pas de réaction négative à cette plante, auquelle il y a parfois des allergies. Je suggère qu'on frotte la plante délicatement sur la peau et attende plusieurs heures; si la peau réagit, ne pas ingester la plante. Il faut toujours faire attention en ingestant des plantes sauvages et je n'encourage à personne de consommer des plantes sauvages sans s'assurer de n'avoir aucune allergie dangereuse et d'avoir aucun doûte de l'identification de la plante.

L'herbe à dinde est utilisée pour traiter de divers conditions et maladies. Un petit dix minutes avec Google montre que le monde crois à toutes sortes de bénéfices à cette herbe. Je vous encourage à évaluer les prétentions avec caution; beaucoups de ces prétentions ne sont aucunement prouvés et il faut exercer son jugement pour évaluer l'évidence. Nous savons que l'herbe à dinde contient de l'acide salicylique, qui peut réduire la fièvre et réduire la douleur. Il faut se souvenir qu'il est très difficile de contrôller la dose d'une substance qui se retrouve dans une plante sauvage et que ceci n'est pas un bon substitut pour des médicaments à dose controllée.

A. millefolium lateral view

Yarrow (also called: arrowroot, bloodwort, nosebleed, soldier's woundwort, & many other names)  is a very common plant in this region. It's easy to identify and as a tea was used by aboriginal people to reduce fever and help with sleep. I put this plant in my herbal teas, but it tastes quite strong so I suggest that people use it only moderately in tea unless you want your tea to taste like nothing else. It can cause allergic reactions so I would suggest that you rub some on your skin and check back in a few hours to see if you have a reaction before ingesting it. Also, the usual disclaimer about not ingesting wild plants if you have dangerous allergies and never to ingest a plant you don't have an absolute positive identification of.

There are a lot of claims all over the internet about the various (semi-miraculous, to hear some tell it) properties of yarrow. I would recommend that these claims be judged on their merits and on the weight of the evidence. We know that yarrow does contain salicylic acid, so the fever reduction and pain relief properties are likely to be true. All other claims need to be similarly evaluated on their merits. It's important to remember that even when we know that a plant contains a compound with known medicinal properties, the wild plant will always be a worse form than the pill because of issues controlling dosage; yarrow tea is not an improvement over acetaminophen, it's a step down because dosage is not known (less effective and less safe;  if you have the pill, don't substitute the herb).

A. millefolium bottom view

I'm taking time at the lake to try to recuperate. I'm working away at a number of things. Saw a deer with two young this morning. I'm snuggling my grumpy old Molly cat, who seems old now in a way she didn't last year. Still, I suppose she had to start acting like an old cat sometime and I guess if she starts in her 20th summer I shouldn't complain. I have a sense of permeating loss, the feeling of summer fading away into autumn... It's a strange feeling to experience combined with the excitement of changing my program and pursuing what I really want out of life.