Drill, Baby Drill! The Ins and Outs of Ichneumon Wasps (Photos by Cheryl Osgood)

A couple of days ago I spent several hours deep in a forest in the Cuyahoga Valley National Park, near my home in northeast Ohio. I was with my good friend, fellow photographer and nature lover Cheryl Osgood (aka Grasshopper). We were searching for photogenic mushrooms, which had begun to appear in the woods following a period of rainy days. We found and photographed some stunning violet cortinarius mushrooms, a nice display of orange sulphur shelf, and several types of boletes, which have tubular pores instead of gills on the underside of the mushroom cap.

Giant Ichneumon Wasp, Megarhyssa Macrurus — Photo by Cheryl Osgood

We were working near the base of a dead maple, which had a variety of bird’s nest fungi, jelly fungi, and other mushroom species growing on it, when Grasshopper let out an excited “Oh my God!” and pointed to a section of the disintegrating bark of the tree a few feet up from the ground. Perched on the bark was an extraordinary creature, a large black wasp, almost two inches long, with a yellow head and legs, a large abdomen, and an incredibly long “tail”, more than three inches long. The insect was braced with its legs against the tree trunk, looking like a miniature black and yellow drilling rig. The light was too dim for natural light photography, and Grasshopper quickly began shooting a sequence of photos with her macro lens and flash while I juggled with the flash settings on my Nikon camera; unfortunately I had not brought the ringlight I prefer for insect   photography. I managed a couple of so-so photos, but Grasshopper recorded the entire sequence of what turned out to be the unique egg-laying process of the Giant Ichneumon Wasp, Megarhyssa atrata.

Megarhyssa atrata beginning to drill hole in tree – – – Photo by Cheryl Osgood

Ichneumon means “tracker” in Greek, and it’s an apt description for these predatory wasps, which use their long antennae to locate the larva of another wasp, the horntail wasp, Tremex Columba, several inches deep in the tissue of dead trees like the maple  next to us. The female ichneumon wasp constantly taps the surface of the tree bark with its attennae, until it detects some combination of odor and/or sound that signals the presence of a horntail wasp grub in a cavity deep in the wood of the tree. Then the wasp inserts the tip of its prodigious ovipositor precisely at right angles to the tree surface and begins to drill a hole down into the tree. The membranes of her lower abdomen twist into a disc and a special fluid is secreted that helps to dissolve the woody material as the ovipositor works its way down in the tree tissue, honing in on the horntail wasp larva. The ovipositor actually consists of three tubes, two of which serve as a sheath that houses the drilling tube and helps to guide it and and protect it when not in use.

Megarhyssa atrata laying her egg on the horntail wasp larva – – – Photo by Cheryl Osgood

When she reaches the horntail wasp larva, the female ichneumon wasp sends its tiny, almost fluid eggs down the ovipositor and deposits them on the surface of the larva. The eggs do not hatch immediately, but bide their time until the horntail wasp is almost fully grown.  When the ichneumon wasp larva kills its host, it is a slow and gruesome process. After the egg hatches, the larva gradually consumes the horntail grub. Like a cat playing with a mouse, it keeps its victim alive as long as possible by eating the non-essential fat of the larva, then the stomach, leaving the heart and central nervous system untouched. Finally, these remaining organs are eaten and the victim dies, leaving an empty shell in which the ichneumon wasp may choose to pupate for the winter, before transforming into an adult ichneumon wasp and eating its way out of the tree the following summer. Adult giant ichneumon wasps do not eat at all, devoting their short lives to mating and egg laying.

Megarhyssa atrata withdrawing ovipositor – – – Photo by Cheryl Osgood

Charles Darwin had difficulty accepting this process, and wrote to Asa Gray in 1860: “I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars…”

The drilling and egg laying process may take more than an hour, during which time the female ichneumon wasp is at the mercy of several predators, including chipmunks, birds, and robber flies. In addition, other species of parasitoid wasps may use the holes drilled by the female ichneumon wasp to lay their own eggs on the horntail wasp grub, thus denying the ichneumon larva its sustenance.

Megarhyssa macrurus showing length of ovipositor – – – Photo by Cheryl Osgood

More than 3,300 species of ichneumon wasps have been described in North America, making identification extremely challenging. However, there are only 4 species of Giant Ichneumon wasps in the genus Megarhyssa. The most common species, Megarhyssa macrurus, shown above and in the first photo, is yellow, orange, and black, and the female’s ovipositor is up to 3 inches long. The larger Megarhyssa atrata, shown in the drilling and egg laying sequence of photos, is mostly black, with a yellow head and legs, and has an ovipositor that may be 4 inches long. Although giant ichneumon wasps have a fearsome appearance, they are harmless to humans. Both species of ichneumon wasps may be drilling holes and laying eggs simultaneously in the same dead or dying tree, and many males may be seen flying around the tree waiting for the chance to mate with a female of their species about to emerge from the interior of the tree.

These remarkable insects give new meaning to the phrase “Drill, Baby, Drill.”

Special thanks to Cheryl Osgood for the opportunity to share her outstanding photographs of ichneumon wasps.





This Post Has 4 Comments

  1. Outstanding information and photographs as well as the identification of and even the opportunity to photograph this was an outstanding gift. As an unbeliever in God as Creator, Darwin did not understand that animals were all vegans prior to the fall of man, and all animal behavior changed due to sin entering the world when Satan usurped Adam’s authority over the earth. In God’s Messianic Kingdom to come, the lion will again eat straw like the ox, the Bible says, and animals will no longer hurt nor destroy. They will again be vegans. Darwin lost his opportunity to see clearly by blinding himself to the truth through his unbelief. If you look at the wasp’s reproductive behavior, this is a great lesson on the nature of sin, how it consumes everything, including itself. Lessons in nature are like biblical parables in that they are more clearly understood by knowing the scriptures.

  2. I should have said on the nature of evil, not the nature of sin.

  3. I am glad I was able to find out about this wasp. I found one doing its “thing” on a stump of a tree outside my back door. I was so intrigued that I video taped it with my phone for about 3 minutes! I never saw one before!

  4. July 21-22, 2014
    I had one in my back yard here in Texas. They are amazing to watch. We recently had a bad storm and it took one of our trees down. We watched him for two days. She was very busy. could have been there longer who knows. She didn’t seem to mind we were sitting close to her work station.

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