Friday, September 23, 2011

Aculeata Agonistes: When hornets are not

Dolichovespula adulterina - a blackjacket and a social parasite

At various times over the last few years, the Home Bug Garden has been blessed with the visits of 10 species of social wasps* – all members of the vespid subfamily Vespinae. Paper Wasps in the subfamily Polistinae, such as the Polistes species common in much of North America, do not occur in Edmonton. Perhaps the introduced European Paper Wasp Polistes dominula (Christ, 1791) may be able to survive our winters, but so far it hasn’t shown up and the nearest Polistes species is in southern Alberta.
Polistes dominula an introduced and spreading paper wasp
 Most years, if not exactly welcome, hornets and their kin are greeted with some interest by the HBG, at least early in the season. Mostly hornets go about their business hunting insects. Some times their prey are pests and sometimes not (e.g. hover flies), but all in all they are as interesting and unassuming as most of the insects in the HBG. 
Yellowjacket worker chewing-up insect prey (a planthopper of some kind)
Telling one species of wasp from the other isn’t easy, except for the Bald-faced Hornet Dolichovespula maculata which is about twice the mass of the next largest social vespine. It is also black and white – but so are other species of both Dolichovespula (D. adulterina - see picture at top) and Vespula (V. consobrina) and yellow and black species occur in both genera too.
A Bald-faced Hornet - the largest blackjacket
 The easiest way to tell the two genera apart is by close inspection of the area between the eye and the mandible. Just what one would like to do – stick your nose in the face of a hornet! Dolichovespula have a relatively large distance between the bottom of the eye and the top of the mandible and Vespula have eyes that almost meet the mandibles. I’m sure one can get pretty good with practice, but for most of the summer being too nosey runs one a strong risk of getting stung.
A Dolichovespula - eye and mandible well separated
 As the summer progresses yellowjackets, blackjackets, and hornets become more and more common. Towards the end of the season, their numbers seem to explode for a few weeks – and then they are gone. This year, though, their appearance was much delayed and when they finally arrived, only three species were present: D. maculata, D. arenaria, and V. pensylvanica. The first and the last of these can be pretty annoying – they will scavenge and so anything you eat or drink is of interest to them – and if you get one annoyed enough, you may encounter the venom delivery machinery at the end of the female workers.
Vespula pensylvanica Western Yellowjacket worker
 At the moment, though, the risk of being stung is pretty low, at least in my backyard. We haven’t had a hard frost yet, so worker wasps are still active, but 95% of the yellowjackets in my backyard for the last week or so have been males. You can easily tell a male wasp from a female, because males have antennae with 13 segments and females have only 12! Also, the males have 7 apparent abdominal segments and females only 6. Easy right? If all else fails, there is a bioassay. If you capture a wasp in your hand and then experience a sharp and violent pain (followed by a strong systemic reaction and death if you happen to be allergic), then you probably have a worker (the new queens mysteriously disappear soon after mating). If not, you may have a male.
Male (note 13 segmented antennae, 7 segmented abdomen) Western Yellowjacket
 The last time I was stung by a vespid, an Australian paper was in the genus Ropalidia, I experienced a strong local reaction. That may not mean much – in Australia a variety of ants, wasps, and bees stung me – but it may indicate a developing allergy. It is always best to avoid being stung. That is one reason I stomped the male in the picture below with the exposed claspers. With claspers instead of a sting, I was pretty sure I had a male, but calling it a hornet made less sense.
A male -  the claspers prove the point

 *Home Bug Garden Vespine Wasps:
Dolichovespula adulterina (du Buysson, 1905)
Dolichovespula arenaria (Fabricius, 1775)
Dolichovespula maculata (Linnaeus, 1763)
Dolichovespula norvegicoides (Sladen, 1918)
Vespula atropilosa (Sladen, 1918)
Vespula austriaca (Panzer, 1799)
Vespula consobrina (de Saussure, 1864)
Vespula germanica (Fabricius, 1793)
Vespula pensylvanica (de Saussure, 1857)
Vespula alascensis (Packard, 1870)

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