Sunday, September 6, 2009

Biodiversity Gone Good: Our Friendly Wasps

Friendly?, well, I exaggerate a bit, but after the last posting on evil hornets, I thought I should exonerate all those wasps (Order Hymenoptera) that wouldn’t hurt us unless we really, really were asking for it. These are the so-called ‘solitary wasps’ – and in going it alone is their secret for getting along with us. Actually, I probably have that backwards: we tend to get along with solitary wasps because they can’t, and have no reason to,  gang up on us.

Like their freedom loving relatives, the ‘eusocial’ ('good', but actually bad, social) yellowjackets and hornets start out as solitary wasps each Spring when queens do all the normal wasp work themselves – find their own food, find a site for a nest, build the nest, lay the eggs, protect the nest, and feed their offspring until they are ready to pupate and become adults. Sounds all very noble and hard-working, but in reality queen yellowjackets and hornets aren’t adverse to stealing another queen’s nest and murdering the owner. In either case, the noble queen or insidious usurper rears grubs that develop into a worker cast – an army of so-called ‘non-reproductive’ or ‘sterile’ sisters (actually ‘suppressed’ would be a more accurate adjective, since workers may reproduce) that do all the work from then on and all the stinging.

These eusocial wasps have modifications in behaviour, chemicals, and stinging apparatus that have evolved to help defend large nests full of their sisters, half sisters (assuming their moms aren't monogamous), and drones. In fact, they have to defend that nest, since the chance of being able to found a new one is probably slim (and perhaps also the reason that stealing nests is common). Unfortunately, when they defend the nest against us, we suffer. Wasps that haven't become social, however, are much less aggressive. So, cheers for the solitary wasps!

Solitary wasps come in two forms: the hyperdiverse parasitic wasps (Ichneumonoidea and more) and the hunting wasps that are close relatives of the eusocial bees and wasps (and ants). Each female hunting wasp must build their nest(s) alone (males just dangle around), so the nests are small, and there is no other wasp to come to its aid if it is attacked. If fact, in spite of all the care and attention a hunting wasp mom will devote to rearing its offspring, it will never see them as adults and has no hope of recruiting them to defend a nest.

Thus, overly aggressive hunting wasps would tend to come to a bad end, but those with a more philosophical attitude, can move on, start another nest, and send daughters and sons into the next generation. That doesn’t mean they won’t put up a bit of a fight, many are capable of delivering a painful sting, but in general they aren’t going to slug it out with something as large as a human. It also helps that solitary wasps are only really interested in hunting down spiders or insects to feed their grubs and an occasional sip of nectar at a flower to keep them going. When a solitary wasp finds you at a picnic, it is most likely because you have attracted flies (which many take as prey) or you have put your blanket over their nest in the ground and they can’t find their way home. Some solitary wasps are members of the Vespidae, the home of hornets and yellowjackets, or close relatives like the mostly black spider hunting wasps in the Pompilidae, but most belong to other families.

When I was a kid and got to read excellent books like Wasp Farm by Howard Ensign Evans (sadly, now out of print - but try the library), the non-vespine hunting wasps all fit in one family, the Sphecidae. Now, alas, most of my bug reading is condemned to papers in scientific journals where any delight has been rigorously suppressed and the information is highly refined - like white sugar, but without the sweetness. Oh well, “Gracefully surrender the things of youth” and that includes a monolithic Sphecidae. The current hypothesis includes three families, and the one we definitely have in the Home Bug Garden, the Crabronidae are considered the sister group to the bees and only more distantly related to other hunting wasps. They do look a bit like bees, but go about their business stuffing flies, caterpillars, bark lice, or the like into their nests instead of pollen and honey. The Crabronidae has some giants, the Cicada Killer (Sphecius speciosus) being perhaps the most famous, but the largest I have seen in the HBG is about an inch long Bembix americana. This wasp nests in sand and feeds her grubs fly after paralyzed fly. I’m not sure what she was doing on a goldenrod in a yard surrounded by oppressive clay soils as far as the eye can see – but she now sits on a pin in a museum. I don’t have any pictures, but my friend The Bug Whisperer has an excellent shot of another, more fortunate, B. americana feeding at an aster.

Most solitary wasps, however, limit their parental care to choosing a host and ovipositing an egg. No nests are involved. These parasitic, or better, parasitoid wasps have no nest to defend, and their egg laying organ, the ovipositor (i.e. egg placer), is used to lay eggs in or on their prey, not to sting annoying humans. 'Parasitoid' is preferred in scientific circles because the end result is almost always a dead bug (whereas a parasite is happier when you keep on living – think head louse). Check out the aphid mummy above perving the mating Ancistrocerus parietum – it may look like an aphid, but it is just a hollow shell with a parasitoid wasp grub inside, undoubtedly a tiny member of the Ichneumonoidea (Ichneumonidae, Braconidae). Although I find hunting wasps more interesting,  it is the parasitoids that make up most of the - unidentified - species diversity of wasps in the HBG.

As far as we are concerned, parasitoid wasps are usually entirely good, except they are difficult to identify and their prey can expect a gruesome end – being eaten alive. That, however, is the fate of the prey of all wasps, including the paralyzed prey of hunting wasps or the mashed up prey of the social vespids. Well, if you want to nitpick, I guess hornets just cut-up insects alive, sort of like Dexter, and then feed the mashed bits to their grubs: nature ocher in sting and mandible. As long as the victim is an insect, though, do we really care?


  1. Excellent summary of this marvelously diverse order.

    I'm probably one of the few people in the world who has come to consider parasitic wasps as "pests" - I groan everytime I open a rearing container into which I've placed beetle-infested wood and see not a brilliant, coppery jewel beetle, but a slew of wispy braconids or chunky chalcidids :)

  2. Hi Ted,

    Thanks, and I can somewhat identify with your feelings. Earlier this year I was delighted to learn that a wispy wasp on my yarrow was none other than a Gasteruption, a member of an early derivative group of parasitoids now placed near the ensign wasps. Then I found out that the Gasteruption was probably a klepto-parasitoid of my solitary bees! For some reason, I feel very protective of 'my' bees, although I don't do anything to help rear them other than provide food. Then there are all those bee flies - I bet most of them are up to no good.

  3. I live in NC and have lived in Florida as well. I have come to really Have respect for bees and wasps. As long as I don't get swarms I love the bees and wasps. I had the experience watching a bee get drunk. Just a drop of Kahuah. I am constantly aware if their homes are being blocked so I make it possible for them to have easy access. I have earned the trust of a mud dauber while she made her nest and experienced seeing the larvae. Here in NC they fly on me and walk over me and my hands. I have had to pull them out of webs and help them get the webby stuff off. Other people get shocked and say are you crazy? I say no, they are my friends. I even think a mother allowed her babies to come near me. (LOL! What's wrong with me?).