Dragons & Damsels: Odonate Overlap

Although killing frosts struck on 17 September, a week before schedule, after this Summer, September was quite a pleasant month. October has been up and down, and not much greenery or insects are in evidence, but the pond bubbler is still on. I usually chicken out in the first or second week of October, but the pump has persevered for 5 summers and probably won’t last that much longer anyway. So, for the benefit of the resident ‘native’ birds (chickadees, red and white breasted nuthatches, house finches, blue jays, and magpies), I’ve kept it going. Soon, though, I will have to give in to the ice gods.

So, what better excuse on a cool, but sunny Saturday, to post about some aquatic insects – and also, to start answering a question that Middle Earth Garden asked back in March – just how similar is the Home Bug Garden fauna to other more natural systems in Alberta? Her question is actually far more interesting than I can attempt to answer. I’d love to spend my summers wandering Alberta and documenting the various insect faunas, but so far no one has offered me a job doing so. However, I do spend many of my weekends at our Moose Pasture and at least for certain groups, I can now make reasonable comparisons between the HBG and the MP. (NB – pictures with blue borders are from the Moose Pasture, no colour borders from the Home Bug Garden.)

 First up is the Odonata. Even the smallest adult odonates are relatively large (or at least long) insects, often very abundant, and not as leery of people as many others. Thus they are more obliging to the photographer and especially friendly for close-focusing binoculars (I like my Pentax UCF XII). BugGuide has many good pictures and even better, for Christmas I got an excellent guide: Dennis Paulson’s Dragonflies and Damselflies of the West (2009, Princeton University Press).

Paulson’s field guide has a distribution map for each species with the species descriptions and pictures – so likely from unlikely species are easily separated. As well as color pictures of mature males and females, plates with line drawings showing male genitalia (claspers) and critical female characters are presented for easy of comparison. Each species has paragraphs with a description and a review of key characters in comparison to similar species. Also, the natural history, habitat, flight season, and a comment on distribution are given. The only complaint I have is that he relies too much on the common, rather than the scientific names – but this complaint may be restricted to entomologists.

Odonate Family Genus species   Moose Pasture  Home Bug Garden

Aeschnidae Aeschna interrupta                +                +

Aeschnidae Aeschna eremita                      +                 -
Corduliidae Epitheca spinigera                   +                -
Libellulidae Leucorrhinia cf hudsonica        +                 -
Libellulidae Leuchorrhinia intactor             +                -
Libellulidae Libellula quadrimaculata       +                +
Libellulidae Sympetrum internum             +                +
Libellulidae Sympetrum danae                  +                +
Coenagrionidae Coenagrion resolutum     +                 +
Coenagrionidae Enallagma cyathicerum      +                -
Coenagrionidae Enallagma ebrium              +                -
Coenagrionidae Nehallenia irene                  +                -
Lestidae Lestes congener                             +                -
Lestidae Lestes disjunctus                          +                 +

Lestidae Lestes dryas                                  -                 +

(excuse the drunken columns - Blogger seems to have trouble with tables. Bold = shared species. Red = HBG only)

As usual, you should take all my identifications with a grain of salt, but in this case if there are any errors, they are probably applicable to both sites. Also, we have many unidentifiable pictures of damselflies, so their actual diversity is probably higher. With damselflies, and I suppose this is ironic, dead males on a pin are the best route to a solid identification.

 So, of the 15 species identified to date, 6 occur both at the Moose Pasture and in our backyard, and only one, the Emerald Spreadwing (Lestes dryas) has yet to be identified at the Moose Pasture. A quick reading of Paulson suggests two reasons for this apparent difference. The Emerald Spreadwing favours shallow densely vegetated ponds (sounds like our backyard pond) and oviposits in live sedges, grasses, and horsetails (the pond is full of sedges). Permanent water bodies are not favourable breeding sites for this species.

Although our backyard pond has only about 2 m square of surface area, it does have lots of emergent vegetation and the bubbler to keep it aerated. At the Moose Pasture, Dancing Elephant Lake (DEL) and its attendant marsh and pond cover about 28 acres. The topography results from stagnant chunks of glacier that were left behind the main retreating mass and formed kettles surrounded by knobs (now covered with aspen) There is much emergent vegetation, and also lots of aquatic marcophytes and some deep areas without vegetation.

The difference between a lake and a pond isn’t well agreed, but usually lakes are expected to be larger and have some area too deep for rooted plants, and DEL seems to just qualify. One of the neighbours calls it a slough, but ‘slough’ is as loosely used as ‘lake’ for everything from an alkaline prairie pothole, to a treed swamp, to a marsh. The only trees in DEL are the skeletons of the willows drowned when the beaver flooded out the meadows that we now call marsh, which to us means it is weedy and shallow enough that getting the canoe through is difficult (The Trunk and Lower Legs). But whatever you want to call it, a host of odonates emerge every year.

The same is true for our backyard pond. Well, maybe ‘host’ is an exaggeration. However, we do have yearly emergences of many damselflies and some dragonflies. It is a rare summer day that one or more of these attractive and useful insects isn't around. They eat other insects, and so we can think of them as good ‘natural enemies” – and if they take any bees, it is only the tiny ones.

And what can we conclude, if anything, from this data? I’ll argue that even a small backyard pond can act as an urban refuge for a subset of the local odonates. This exaggerates the usefulness of the pond for dragonflies – the 4-spotted Skimmer was a one-off (possibly brought in with a plant) and the Variable Darner (Aeshna interrupta) may cruise through your yard even if you don’t have a pond.

 The Cherry-faced and Black (S. danae) Meadowhawks, however, breed in the pond as do several of the bluet damselflies. The Emerald Spreadwing finds a small pond a perfect habitat. In Edmonton, where synanthropic mosquitoes that breed in small accumulations of water are absent, there is no real downside to a backyard pond – the birds love it, the bubbler adds some relaxing white noise, water plants are interesting, and a host of aquatic insects, snails, and other even smaller invertebrates can make a living where dandelions and grass once dwelled.

Aculeata Agnoistes: The Prairie Yellowjacket Vespula atropilosa

In general, I try to adorn this blog with as many of my wife’s pictures as possible. After all, she is the photographer (and the one with the cumbersome and expensive camera gear). I’m strictly the put-a-name-on-the-bug person. And when it comes to cameras, I’m strictly a point-and-shoot person. As a result, I rarely come up with an insect picture that is of much use. This isn’t entirely the camera’s fault – people like Terry Thormin and an earlier Ted MacRae (who has now moved on to a real camera and even more spectacular photos) have produced numerous great insect photos with point-and-shoots (and Alex Wild can even produce good pictures with a cell phone) – but for anything that isn’t large and slow-moving, putting me and a point-and-shoot (originally a CoolPix 5700 and now a Lumix DMC-FZ28) after them is mostly a lesson in humility. To me the worst affliction of point-and-shoot insect photography is the interminable delay between pressing the button and the camera snapping the picture.

In this case, a colony of the Prairie Yellowjacket Vespula atropilosa under the steps in the garden in front of Government House, my wife was not around and I had to be the photographer. I won’t share the two dozen beautifully focused pictures of the wasp-less steps with you. Still, with enough persistence and cooperative bugs, even I can acquire images adequate to document the identity of an insect. Usually I would use the Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region to identify a yellowjacket. However, as is true of so much of Canadian life, the Atlas only works for species in the East. The Prairie Yellowjacket is a western species and reaches its northeastern distributional limit in Edmonton: it isn’t in the key.

If you used the Atlas more or less correctly, you should end up in the rufa species-group before your started to founder. The two yellow spots on top the first abdominal segment are helpful – if mostly fused to the posterior yellow band. If you made some wrong choices, you might end up in the vulgaris species-group and start to feel like I do when using my point-shoot to take a picture of an insect. When the characters on your insect and those in the key start to diverge widely, it is usually a sign that somewhere you have made a wrong choice.

Learning the true name of a yellowjacket may seem like a bit of an egghead thing, but if you were trying to decide if you needed to eliminate the nest, it could be quite useful. In general, rufa group yellowjackets mind their own business and spend their time hunting insects to feed their brood. That means you could consider them useful ‘natural enemies’. If you stir up the nest, yes they will attack and sting you (so will bumblebees), but otherwise you might hardly notice them and probably most of what they eat wouldn’t be missed.

Vulgaris group species, however, will both hunt and scavenge and are quite willing to share whatever you are trying to eat or drink – and if you object, they are happy to sting you. They also have larger colonies and tend to be more aggressive. Every spring I eliminate any vulgaris group species trying to take up residence in my yard. This usually means the Western Yellojacket Vespula pensylvanica (it gets just east enough to be in the Atlas). I also take out the Baldfaced Hornets Dolichovespula maculata. In contrast to species of Vespula that tend to nest underground, Dolichovespula tend to nest in trees and shrubs (or on fences) where you are more likely to bump into them. The Baldfaced Hornet is the largest and most aggressive member of its genus and it pays to go after the nests when they are small.

Like other members of its hunting group, the Prairie Yellowjacket tends to nest underground and to have smaller nests than vulgaris group species – a few hundred rather than a few thousand workers. Unfortunately, although “restricted to the Canadian and Transition Zones of the Boreal Region”*, the Prairie Yellowjacket is also happy with the open areas we create such as golf courses and parks, so even if you mind your own business you may encounter this wasp. You can learn a fair amount about it – and even have a good chance of keying it out correctly – if you consult Akre et al. (1981)*, one of those great monographs that the USDA used to produce. You can also find most of the information and illustrations from this book on line at Discover Life. I suppose I might regret it, but if a Prairie Yellowjacket decided to nest under my steps, I think I’d let it.

*Akre, R.D., A. Greene, J.F. MacDonald, P.J. Landholt, and H.G. Davis. (1981). Yellowjackets of North America, North of Mexico. U.S. Department of Agriculture, Washington, D.C. Handbook #552.

Aculeata Agonistes: Ants, Aphids & Aspen

The Home Bug Garden doesn’t look like the picture above, that is of our Moose Pasture about 55 km to the East as the raven flies, but it may once have. Both are located in the Aspen Parkland biome, named for its dominant tree, Quaking Aspen (aka White Poplar) Populus tremuloides, and its park-like mixture of open grasslands and patches of trees. In the Prairie Provinces of Canada, Aspen Parkland is rich in postglacial water bodies. And, as my late father-in-law pointed out repeatedly, he used to going boating in what is now our neighbourhood when he was a boy.

The prairie parklands occur across a broad stretch of central Canada, but aspen parkland also extends well to the south in the Rockies. South Park in Colorado, made famous by the potty-mouthed cartoon, is just one of many such mixtures of aspen and meadow. Interestingly, parkland is considered a transitional biome between prairie and boreal forest. It’s as if it isn’t really a natural system, but somehow aberrantly refuses to become its destiny: conifer forest if moisture remains high enough and fire frequency low enough or prairie if the opposites occur.

We love aspen, but whenever I find a seedling growing in the HBG, I grub it out. This is an entirely practical behaviour: aspen roots have a reputation for seeking out and clogging water and sewage pipes. Unfortunately, that means we miss out on a lovely tree and all but a passing acquaintance with many of the insects associated with aspen. Not all though, there appears to be at least one aspen-associated aculeate hymenopteron that finds both the Moose Pasture and our yard agreeable: the Black Mound Ant Formica podzolica Francoeur, 1973.

In zoological nomenclature, the year that comes after the author of a species name refers to when the diagnosis of a new species was first published. In this case, I haven’t inverted the 9 and 7 – this species name wasn’t properly sorted out until 1973. Before that it travelled under several names including the widely distributed Formica fusca. Insects tend to be interesting in direct proportion to how much one can learn about them and unless one can first learn their real name, such information as to make them interesting neighbours remains elusive. Ant species are particularly difficult to identify – species level keys are technical, and, well, many ant species tend to look alike. This seems to be especially true of Formica species. In this case, we are indebted to James Glasier for identifying the black ants that caught our attention with their herds of speckled aphids on young aspen as Formica podzolica (misattributions in any other images are mine).

Although the scientific name may be relatively new, people in my neighbourhood have been at war with black mound ants since soon after the first expanses of green lawns rose out of the former slough. Formica podzolica excavates and piles up largish mounds of black clay wherever it feels at home here and no one seems to find lumpy lawns attractive or interesting. In the bush, though, the mounds are an interesting feature and the black ants seem much less aggressive than their red and black neighbours Formica aserva.

I’m less than excited by ants, but no lover of lawns, so generally I leave my ants alone as long as they leave me alone. Unfortunately, ants are infamous for guarding patches of sap-sucking homopterons (aphids, hoppers, and the like). They protect these annoying insects from ‘natural enemies’ such as ladybird beetles, lacewings, and small parasitic wasps. ‘Natural enemy’ is another of those bizarre concepts that has somehow become commonplace. Are there unnatural enemies? Well, I suppose Count Dracula’s cockroach-munching Igor would do. In any case, usually ‘natural enemy’ refers to an arthropod that eats or parasitizes an arthropod that eats something we value. Ants can be natural enemies, but not when they are guarding aphids. By chasing off or killing things that want to eat aphids, ants allow plant lice (= aphids) numbers to rise, the amount of sap they drink to increase, more honeydew to spatter, and sooty molds to cover leaf surfaces. None of this would seem to be good for the plant, but the ants benefit by ‘milking’ the aphids for their honeydew and the aphids are assumed to do better with the guards.

Two things especially intrigued us about the black ants and their aphids on the young aspens, and the first was that the aspen leaves have a pair of nectaries (red spots where the petiole joins the leaf under the leg of the top ant). That plants can produce nectar in flowers to attract pollinators is well known, but nectar-producing glands are not limited to flowers. As a group (and giving an indication that scientists were once surprised to find this out themselves) nectaries not in flowers are called ‘extrafloral’. Ants are known to be attracted to extrafloral nectaries, and one can imagine that having aggressive black ants scuttling around one’s peony buds could be a good thing when some hungry caterpillar was on the prowl for a meal. But why would aspen want ants on their leaves if they end up tending aphids? This particular aphid is a well known pest of aspen – the Poplar Leaf Aphid (aka Speckled Poplar Aphid) Chaitophorus populicola (thanks to Bryan Brunet for the id).

Fossils in the Florissant beds in Colorado demonstrate that members of the genus Populus have had nectaries and been associated with ants and other predatory insects for at least 35 million years (Pemberton 1992. American Journal of Botany 79:1242-1246). Just why aspen have extrafloral nectaries, however, isn’t very clear since they do not seem to influence natural enemy abundance (see Wooly et al. 2007. Annals of Botany 100: 1337–1346). Of course, just calling an insect a natural enemy doesn’t make it useful to a plant (or a gardener). Ambush bugs and crab spiders, for example, make their livings hiding in flowers and eating pollinators.

So perhaps we have good natural enemies that help the plant and get their reward at extrafloral nectaries and other bludgers that just take a sip and go about their not very helpful lives. Life, however, is usually not that simple. For example, the usefulness of extrafloral nectaries may vary with age (younger aspen have proportionately more nectaries than older aspen) and time of year (many nectaries are known to dry up after young leaves have hardened off in early summer). So, ants may be useful for keeping caterpillars away in the spring or on young trees (which have fewer leaves they can afford to lose). Perhaps the ants don’t start farming aphids until after the trees cut off their supply of nectar. Perhaps later in the summer, when leaves will soon be dropping anyway, aspen find it less expensive to let the ants get their sugary rewards second hand from the plant lice than to feed them directly from extrafloral nectaries. There are enough ‘perhapses’ in this simple system to keep a host of scientists busy for years.

Speaking of which, Kailen Mooney & coworkers have found out something interesting about our black ant on pine trees in Colorado. There Formica podzolica herds large aphids in the genus Cinara. I once had a job dissecting Cinara aphids and looking for parasites – 10,000 aphids yielded only 3 parasites, so perhaps our black ant is a good Cinara shepherd (or I was a really bad aphid vivisectionist). However, Mooney found that birds were able to eat both ants and aphids, reducing the latter by 91% (those not eaten dropped to the ground) and causing the ant to look for less dangerous meals. That was good for the pine trees, so birds can be elevated to ‘natural enemies’ here. Black Mound Ants were good for the aphids only when birds weren’t around. But as usual, the story is even more complicated. As well as Black Mound Ants, another species in the same genus, Formica planipilis, also guarded pine aphids. This ant was a better aphid husbander even when birds were around (see Mooney & Mandel 2010. Oikos 119: 874–882 and references therein). I’m starting to feel a little bit sorry for the aphids that Black Mound Ants decide to protect.

This feeling is reinforced by a closer look at our erstwhile aphid farmer: several predatory hoverfly larvae are eating aphids right under the noses of the ants! Apparently the ants are oblivious to the foxes in the hen coop, or perhaps too nervous that a Yellow Warbler may swoop down and eat them to notice. Also, they may be being fooled by the hoverfly larva into thinking the maggots are aphids.  Syrphus ribesii uses its cuticular hydrocarbons to smell/taste like the wooly alder aphid and protect themselves from guarding ants (Lohman et al. 2006. Ecological Entomology 31: 41–51) and this may very well be happening here.

If you can think of being tended by ants as a characteristic of an aphid species, then you could ask the question, we’ll I wonder how many times it evolved in Chaitophorus aphids feeding on poplars and willows? Shingleton & Stern (2003. Molecular Molecular phylogenetic evidence for multiple gains or losses of ant mutualism within the aphid genus Chaitophorus. Molecular Phylogenetics and Evolution 26: 26–35) asked this very question and found that it appears to either have been acquired by several aphids independently or to be a fairly unstable character that has been lost multiple times. Considering this particular association and the results of Mooney and her coworkers, one wonders just how beneficial it is for an aphid to be associated with the Black Mound Ant?