Thursday, August 27, 2009

Biodiversity Gone Bad: Hornets in the Home Bug Garden (updated 19 Sept 09)

Home bug gardening isn’t the most easily understood avocation. At work my colleagues make fun of me not wanting to kill the insects in my yard. My revolving neighbours on one side, a rental, persistently think that I am a botanist. No many how many times I tell them I’m a bug gardener, it just doesn’t compute. The neighbour on the other side has known me 7 years now and I thought she understood. But, when I proudly proclaimed to her last week that I had identified 9 species of hornets and yellowjackets from my backyard, she seemed nonplussed, or perhaps creeped-out.

Before someone goes running for the bylaws or the bug spray, let me make one thing perfectly clear: as far as I know, I don’t have any hornets or yellowjackets nesting in my yard. In fact, on the first cold night after finding a bald-faced hornet nest on the fence this Spring, I nuked it. The yellowjacket queen that tried to nest under the garage was first flooded, then buried and, those efforts proving entirely ineffectual, finally netted and smashed. There may be a nest hidden somewhere on my lot, but based on the trajectories of the visiting hornet workers, I’d say I have my neighbours to thank for my astonishing vespine diversity.

And an astonishing diversity it is – it looks like most of the hornet species likely to be found in this part of Alberta are lurking within flying distance of my backyard. Not only that, but they find the Home Bug Garden entirely worth a regular visit. This conviviality is no doubt due to two aspects of the garden: ready access to water and lots of umbels. Actually, there may be a corymb or a cyme or two, and there are certainly some corymb-like (yarrow) and otherwise racemose (goldenrod) clusters of composites that attract wasps, but as I repeatedly tell my neighbours in the rental, I’m really not a botanist. In any case, the umbels clearly get the most attention from simple umbels (milkweed) to compound umbels (dill, lovage, caraway, chervil). The good news is that most of the wasps fooling around on flowers are males – and these can not sting - and most of the ones that can are really more interested in bugs than in people.

Wasp is a general term, but for most people it refers to the social members of the family Vespidae that have the ability, and the willingness, to sting repeatedly when disturbed. This is mostly a behaviour of the workers – the reproductively suppressed females – who have no problem jabbing their modified egg-laying organ (ovipositor) into your skin and injecting lots of toxic and allergenic chemicals. Although it is possible to die of envenomization from wasp stings, almost every one who dies after being stung is a victim of anaphylactic shock and a single sting can kill a susceptible individual. Queens are much bigger than workers, and so more intimidating, but are usually only seen in early Spring and briefly in the Fall. Male wasps are harmless flower philanderers, but look pretty much the same as the workers (actually, they have longer antennae and one extra abdominal segment, but when you have a yellowjacket wanting to share your pop, these aren’t the easiest characters to see). So generally, keeping safe means keeping away from nests and from foraging workers.

The family name Vespidae comes from Vespa, the Latin for wasp, and also the genus name for the Giant European Hornet – a truly large wasp, large enough to feed on honeybees and yellowjackets when it feels like it, pretty intimidating in person, and also having the garden-unfriendly habit of girdling twigs so that it can feed on sap. Unfortunately, the European Hornet, Vespa crabro, was introduced to North America and is well established – but fortunately for Edmontonians, only in the East. Easterners also are well familiar with the paper wasps in the genus Polistes, but the only Albertan species, Polistes aurifer, appears to be limited to the south. That’s good, because Polistes nests are often placed on shrubs, fences, window wells, and other places you are likely to stick your hands without looking, and if you blunder into one, you will get covered by stinging wasps. What we Edmontonians get are Vespula (‘little wasp’) and Dolichovespula (long little wasp – they have a rather long face). Species of Dolichovespula tend to nest above ground in those grey football-like paper nests and species of Vespula tend to nest below ground in old rodent burrows or the like, but there lots of exceptions, especially when it comes to taking advantage of hollow spaces in human habitations.

Before I get into the specifics of my HBG wasps, let me highly recommend these two publications (from which I will borrow information freely):
Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region by Matthias Buck, Steve Marshall, and David Cheung in the Canadian Journal for Arthropod Identification
The Yellowjackets of America North of Mexico. by RD Akre, A Greene, JF MacDonald, PJ Landolt, and HG Davis. 1981. Agriculture Handbook, 552. United States Department of Agriculture, Science and Education Administration, Washington D.C. 102 pp.

UPDATED 19 September 2009: Large V's of gruking sandhill cranes have been flying south over the Home Bug Garden; orange-crowned and yellow-rumped warblers and white-throated sparrows have been splashing around the bird bath; and the leaves are yellowing fast. Yellowjacket season will soon be over, perhaps next week, as frost is threatening. Time to polish up this post and bid adieu to some of our least loved bugs.

No new species to add to the HBG, but Insects of Alberta has records for the Arctic Yellowjacket (Dolichovespula norwegica (Fab., 1781) ) from Calgary, so I'm a bit envious. From the picture, I'd say that 'yellowjacket' is a bit of a misnomer - looks like a blackjacket to me - but nothern populations of vespids (including the solitary species) can tend towards 'ivory' markings.

To continue with the lack of good news, I have been able to confirm that the Evil European Wasp, Vespula germanica, is a member of the HBG vespifauna. The confirmation comes via the male genitalia (no pun intended, or at least not initially), so breeding populations are here in Edmonton. Excess confirmation for this colonization event came the very same day as the HBG event, when a nest was nuked at work and turned out to be V. germanica.

On the good, or at least interesting, news side, I have discovered (more likely rediscovered) a behavioural difference between the males of Dolichovespula and vulgaris-group Vespula. The former are the flower philaderers: greedy, flower frolicking, poseurs in aposematic bands.   The latter, at least for V. pensylvanica and germanica, are very mysterious delvers into the foliage of forget-me-nots - and seem not at all interested in flowers. Details are added below by species.

The Bald-faced Hornet - Dolichovespula maculata (Linnaeus)

These are our largest hornets, the only common black and white ones, and have a definite sense of entitlement. If you try to swat one away, it is more likely to buzz you, than to acknowledge your superiority and move on. They have attitude, but after a few minutes of in-your-face fancy flying, usually find better things to do. The workers take honeydew and other sugary things like pop, but mostly prey on live arthropods (especially flies visiting flowers in my garden) and sometimes preferentially on other hornet species. I watched one bald-faced wrestle another to the ground. I suppose I should have waited to see who won and what happened to the loser, but I was so shocked by the lack of sisterly solicitude that I stepped on both on them. Why can’t wasps just learn to get along? Anyway, the big, grey nests can be found up to 20m above ground in trees but also in or on human structures and in hollow trees. If you come across a nest, I advise you to leave it alone. Let someone else win the Darwin Award.

The Aerial Yellowjacket - Dolichovespula arenaria (Fabricius)

These are about half the size of the bald-faced hornets, and the more typical yellow and black in colour (see plate a few paragraphs above), but otherwise have similar behaviours. Nests are usually in shrubs or trees from near the ground to high in the canopy or in or around our homes. Workers are mostly interested in catching other insects for dinner, so they aren’t the worst guests at a picnic, but like any social wasp, if you disturb their nest, you are in for a bad time. The males are a constant presence on goldenrod and swamp milkweed throughout the late summer.

Northern Aerial Yellowjacket - Dolichovespula norvegicoides (Sladen)

This is my second favourite backyard wasp, mostly because workers are rare and inoffensive and the rest are harmless males feeding at flowers. Also, little is known about their biology except they tend to have aerial nests in trees and shrubs. Rare and mysterious is always more interesting than common and nasty. Males are common on swamp milkweed and early goldenrod in mid-August, but seem to disappear in September.

The Parasitic Blackjacket - Dolichovespula adulterina (du Buysson)

This is by far my favourite backyard hornet because it is the only obligate social parasite in its genus in North America (adulterina is now considered the proper name for the arctica in the USDA book). ‘Obligate social parasite’ means a queen D. adulterina infiltrates a nest of the Aerial Yellowjacket early in the season before the workers emerge, sneaks in its own eggs, and eventually kills off the yellowjacket queen. Now what more could you ask for in a hornet? Additionally, the males are an attractive ivory and black colour and pretty much mind their own business as they pollinate my plants.

The Blackjacket - Vespula consobrina (de Saussure)

Species of Vespula in our region fall into two species groups: the annoying vulgaris group and the laid-back and innocuous rufa-group. The Blackjacket and the next species, the Prairie Yellowjacket, are the only members of the rufa-group I’ve found in my yard to date. The Blackjacket looks a bit like a half-pint Bald-faced Hornet or a Parasitic Blackjacket but has a short face and slight differences in patterning. Like the rest of the rufa-group, these hornets are primarily interested in eating insects and aren’t likely to bother you. Actually, they have never bothered me, but I did kill a worker to confirm the species identification (and alleviate the snickering at work).

The Prairie Yellowjacket - Vespula atropilosa (Sladen)

This is the rarest of my backyard hornets and I don’t have any pictures. Edmonton is near the NE limit of its range. They nest mostly in rodent burrows or in rotting stumps and logs and have an interesting ichneumonid parasitoid, Sphecophaga vesparum burra (Cresson), that lives in its nests and parasitizes its pupae. In Washington State, 80% of Prairie Yellowjacket nests may be infested with the ichneumonid (which also goes after vulgaris-group wasps). Males wander into the HBG on a regular basis, but are difficult to document because they don't seem to have either the flower philandering or forget-me-not delving behaviours of the others. The few I have captured have been on-the-wing or resting on foliage.

The Western Yellowjacket - Vespula pensylvanica (de Saussure)

This is the main pest yellowjacket in my yard and probably in most of Edmonton, although we are near the northern limit of its range (apparently de Saussure had problems with his spelling as well as his distributional information since this wasp does not occur in Pennsylvania). The workers are aggressive, and although they do forage for insects, they also are attracted to dead animals including that burger, hotdog, or roast pig you are trying to eat at a barbie. They like soft drinks too (but seem to give wine a pass) and when you swat them away, they give you the buzz treatment. Nests are built in hollow walls and attics, as well as underground (probably what was trying to nest under my garage this Spring). They have a truly incredible parasitoid – the trigonalid wasp Bareogonalos canadensis (Harrington) – but that is a story for another post. The primary source of Western Yellowjacket mortality in my yard appears to be me, so there are lots of them buzzing my flowers for prey and my barbecue for meat.

Male Western Yellowjackets show an interesting behaviour in the HBG: they seem to like the foliage of forget-me-nots (Myosotis sylvatica). Actually, the foliage is a low and dense garden bed composed of forget-me-not, coltsfoot (Petasites palmatus), and bunchberry (Cornus canadensis), but the males are mostly landing on the forget-me-not (but that is most of the cover).

Once they land, the males crawl into the foliage and disappear. I've put my nose to the ground and watched a couple and they don't seem to do anything other than walk on the plants and perhaps apply their mouthparts to the leaf surface now and then. What is going on? I haven't a clue, but there is no sign of honeydew, queen yellowjackets, or any other obvious attractant, including prey (which presumably they aren't interested in anyway).

I missed these males for a long time, because I assumed they were workers, but nope, they are all males - and none are showing up on flowers. Very interesting - and this is also were I picked up a male V. germanica, so it may be a vulgaris-group behaviour. My current favourite hypothesis is that the males are collecting a plant compound that makes them attractive to females, but it took two glasses of wine for that idea to pop up, so in my current sober state I find it dubious.

The Vulgar Yellowjacket - Vespula vulgaris (Linnaeus)

In its European incarnation, this is the species that gives its name to the nasty vulgaris-group. Ours may actually be a different species, but it has all of the unfortunate behaviours that result in yellowjackets being unwanted guests. Workers go after a wide variety of human foods and kill the occasional bug when they are bored. Nests are usually subterranean but are sometimes also built in rotten logs or stumps, forest duff, hollow walls or even in trees. This is one of the two species of yellowjackets that have been introduced to Australia and New Zealand where they have become an ecological disaster and very annoying pests. In my yard Vulgar Yellowjackets were common earlier in the year, but have now been almost entirely replaced by Western YellowJackets and the next species.

The Evil European Wasp - Vespula germanica (Fabricius)

This species is the horror introduced into New Zealand early on; Hobart, Tasmania in 1958; Maryland, USA in 1968; around Melbourne, Victoria in 1977; and elsewhere around the World on various dates in its unending drive to conquer all. It does well it urban areas, seems to like to eat all the things we like to take on picnic, scarfs up all the sweets it can, and is very aggressive in taking its share of the meal. Nest are usually subterranean but are also built in hollow walls, in roofs, attics, and any other place where it can find an acceptable cavity. The species looks similar to the Western Yellowjacket and especially so here where the Western colour pattern can overlap that of the European Wasp. So far, I’ve collect three probable germanica workers in my yard, but it would be nice to catch a male and confirm that this wasp has indeed reached Edmonton and that we aren’t just seeing a melanistic form of the Western Yellowjacket. Or would it? Well, whatever would be nice, unfortunately I have collected a male, and the genitalia never lie. Males, or make that the one male I have collected, have a similar forget-me-not behaviour to the Western Yellowjacket (see above).