The Chalcid Wasp: Not Your Everyday Pollinator

The diversity of nature is astounding. Even in the small corner of the world that is the Sycamore Greenway--102 acres--there is an amazing number of flowers, birds, insects, and all other variety of life to be seen if one simply pauses to look.

At a walking pace, much of the insect life is invisible. You may see a Monarch fluttering busily through the basins, or hear a chunky bumblebee buzzing around the red clover along the trail. But there is so much more! Stop and look--really look--at the cluster of black-eyed Susan there just a few feet away. How many different kind of bees do you see? And is that a wasp?

What about the wild quinine? Each patch along the way seems to be fairly deserted. But then there is one particular plant that is crazy with activity: bees, syrphid flies, ants, and...dear god, what in the name of all that is holy is THAT?!?!

It looks like nothing so much as an alien shrunk down to miniature size: large mantis-like eyes astride a pair of charming antennae; a rounded and segmented shield on the back of its thorax, and what is up with those crazy hind legs? Chunky thighs curled over dainty, hair-thin feet that seem too small to carry the burden of those legs.

It lingered long enough to get a decent shot for later identification, and then we went our separate ways. At home, Google was an abject failure (there are, apparently, thousands of weird-looking bugs with big hind legs). Plan B--paging through an insect guide--turned up a close hit. The subject appeared to be a Chalcid wasp.

Chalcid wasp (Conura sp.) on wild quinine. Adults may feed on
nectar and pollen; their young have more macabre tastes.

The lifestyle of the Chalcid wasp is as horrific* as its appearance would suggest. They are parasitoids, laying their eggs in their hosts--either the pupae of butterflies and moths or larvae of flies--which then hatch and devour their hosts, killing them in the process. The strangely-large femurs may help the females grasp and maneuver the pupa or larva in which she intends to lay her eggs. Though unfortunate for the host insects, this process is another demonstration of the incredible diversity of life and methods of survival**, and is also useful in keeping populations of pest insects in check.

* I know, it is actually kind of cute from this angle. But it was a jarring sight creeping into few after dozens of adorable, pollen-dusted bees.

** One blog post mentioned the theological conundrum posed by parasitoids like Chalcid wasps in a God-designed world. Fun to imagine this little wasp and its kin being the subject of philosophical debate!

The Naked Branch

I'm not much of a tree person. Although I appreciate many things about them, I am unable to retain many identification cues in my brain, regardless of how many times someone tells me this specific tree is a Black Cherry or that one with the warty bark is a Hackberry.

I like my trees obvious. My favorites are those with comically unmistakable leaves: Catalpas, with their huge, pale green hearts, or Tulip Trees with their vaguely tulip-shaped leaves. Honey Locusts are pretty and easy, with delicate-looking compound leaflets and, in wild varieties, wicked-looking clusters of thorns adorning the trunk.

The naked branches of
the Kentucky Coffee
Tree in winter.

But there is one tree that even I found easy to identify--in winter! There are a few of them planted along the Greenway trail, just a bit north of the Sycamore Apartments: the Kentucky Coffee Tree (Gymnocladus dioicus). The genus name gives a hint as to why it is so distinctive even without its leafy adornments: Gymnocladus means "naked branch" and, when you see a bare Kentucky Coffee Tree, the branches do look rather empty, lacking all the smaller branching twigs you see on many other trees.

They also have distinctive leathery seed pods that dangle from the upper limbs through the winter. About the size of my palm or larger, they are shorter and wider than the pods of the related Honey Locust.  The seeds can be roasted and ground to make a coffee-like drink (hence its common name); however the seeds and pods are toxic when raw so caution is required for any adventurous souls tempted to try this rustic coffee substitute.

Seed pods, looking dramatic.

The leaves themselves resemble those of Honey Locust in that they are compound, consisting of a many small leaflets and sub-leaflets. The leaves themselves are huge, though at a glance they don't appear so since we generally register only the small sub-leaflets as "leaves." Rather, each complete "leaf" can be up to three feet long, with multiple leaflets branching off and each leaflet containing multiple sub-leaflets.

• This illustration at the Arbor Day Foundation's website shows two complete leaves and two seed pods.

The flowers are less spectacular, though still somewhat flashy and interesting if you happen to catch them in the spring.

A cluster of flowers, or panicle.

The seed pods of the Kentucky Coffee Tree are an interesting anachronism. The seeds and pods themselves are toxic and have been known to kill livestock; they are too large to be eaten by birds and too tough to be nibbled by smaller animals (leaving aside the toxic bit)--so why does the tree expend the effort to make these large pods for their seeds, and why is the pulp surrounding the seeds sweet to taste if the seeds themselves are poisonous?

It has been speculated that some critters were big enough and tough enough to consume the pods without suffering ill effects from the toxin, and allow the seeds to pass through (so to speak) and be dispersed throughout the landscape: prehistoric mammoths and mastodons. We may be seeing in our little Kentucky Coffee Tree on the Greenway the remnants of a completely different ecosystem that has managed to hang on in spite of losing its evolutionary partner.

• Read more about "Evolutionary Anachronism" in trees.