What are “spheciform wasps”?

Spheciform wasps (Crabronidae: Philanthus) making more spheciform wasps. (California USA).

In the previous post, I mentioned that Johnson et al (2013 ) determined the closest living relatives of ants to be “spheciform wasps + bees”. I assume we all know what a bee is, more or less, but what is a “spheciform wasp”?

Pison wasps construct nests from mud and provision them with spiders. (Victoria, Australia)

Chances are, you’ve seen them. Spheciforms are everywhere, and their numbers include some of our largest and most colorful insects.

Sphex pennsylvanicus, the great black wasp. (Illinois, USA)

Spheciforms are a diverse assemblage of predatory & parasitic wasps abundant worldwide. Females construct nests to enclose offspring with prey, while the specifics of nest type and prey vary among species. Some fill mud nests with spiders, others stockpile bees in burrows dug into the sand, others stack aphids in nests tunneled through decaying wood. Size can vary from a few millimeters long to well over an inch; one of North America’s largest native wasps, the much-misunderstood Cicada Killer, is a spheciform.

Sphecius speciosus, the Cicada Killer (Illinois, USA)

One particular lineage of spheciform does exactly the same thing- constructing nests and provisioning them with food- only with pollen from plants rather than paralyzed insect prey. This group is the bees. Bees are built much like the rest of the spheciforms, but they have acquired a few specialized traits, like branched body hairs, that aid their pollen-feeding lifestyle and give taxonomists a way to identify them. Thus, bees are just vegetarian spheciforms.

I should also note, as a matter of clarification, what aren’t spheciform wasps. Many animals we often conjure when we think of wasps belong to other, non-spheciform groups. Paper wasps, yellow jackets, and hornets are vespid wasps, tarantula hawks are spider wasps, while the ubiquitous parasitoids belong to many older groups. Velvet ants are also not spheciforms, nor are they especially close relatives of ants.

Johnson et al’s discovery that spheciforms and ants are related is significant primarily from the observation that ants, too, build nests to raise their young. That all the insects in this group make enclosed nests, likely as an ancestral condition, and that this group contains several independent derivations of fully social, fully colonial behavior, should elevate the hypothesis that nest-building is a prerequisite for the evolution of sociality.

Ectemnius sp. (Arizona, USA)

More resources:

(identifications fixed in update, thanks to Doug Yanega and Devon Henderson over on FB)

5 thoughts on “What are “spheciform wasps”?”

  1. How do you identify branched hairs? I keep reading about that as a identification trait for bees, as least for the bees that do have hair, but do you really need a very powerful microscope to see the branches in the hair? Is there a way to tell that the hairs are branched by how the hairs lay on the insect? Maybe you just smear pollen all over it see how well it sticks?

    1. Hi Charles. You do need magnification to see the branched hairs, though it doesn’t have to be super-powerful. I can see them when I look through my Canon MP-E macro lens. Plumose bee hairs look like this: http://www.extension.org/pages/21748/adult-bee-anatomy-basic-bee-biology-for-beekeepers#.UlBALcashLc

      An easier way to tell the difference between bees and wasps is to look at the feet. Especially, the hind feet. The basitarus (that is, the 5th segment up from the tip of the foot) is enlarged and often flattened slightly in bees, where the same segment in wasps is usually simple and cylindrical. Here’s a bee where you can see this trait clearly: http://www.alexanderwild.com/Insects/Insect-Orders/Bees-Wasps-and-Sawflies/i-Cd2mtp7/A

  2. Nest building leading to sociality makes sense and has been a strong hypothesis, especially considering that all eusocial aphids and thrips live in galls (not to mention wood inhabiting termites). Thus the close quarters and protecting of a shared space lead to castes, brood care and overlapping generations. Cool findings!

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