Mating for Death | Salmon | Praying Mantis

A more familiar organism, the Pacific Coast salmon, has a life cycle like the lamprey's. It begins its life invariably in fresh water, grows up a little way, and then goes through a first metamorphosis, losing its spots and nice colors. Up to that point it had looked like a freshwater trout. Now it turns silvery, and goes to sea, where it grows up.

At sexual maturity it metamorphoses again, the flesh becomes pink, its color changes. There are all kinds of changes, including again a complete collapse of the digestive system. These salmon, before beginning their migration upstream, are through with eating. They will never eat again.

In fact, in many of the males, the jaws become deformed, so that they can no longer meet. This animal isn't interested in jaws anymore. In this way it begins its journey upstream. It is no fun. The bears are waiting for it, the Indians are waiting for it, the sportsmen are waiting for it, the canning industry is waiting for it.

Those handsome travel folders show you the salmon leaping over falls. That is no fun either. They beat themselves to pieces doing that kind of thing. The salmon that reach the spawning grounds are already dying organisms. They're all torn up, with great wounds in their sides which bacteria have invaded. They are capable only of that last act of reproduction, and that's the end of them.

So it is all too clear in these organisms and many others that reproduction is the last act of life, and that the preparation to reproduce is simultaneously the preparation to die. Sometimes death doesn't wait for the act of reproduction to be accomplished, but takes part in the act.

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There was a golden period of insect observation in the second half of the nineteenth century. We had Henri Fabré in France, August Forel in Switzerland, Sir John Lubbock in England, and Maurice Maeterlinck in Belgium who wrote about the life of the bee. While these biologists were watching insects so intently, great interest was aroused in the habits of the praying mantis.

The praying mantis is a voracious animal. It will tackle something much bigger and stronger than itself, and usually wins. It was observed that when a pair of mantises is copulating, the female, which is a much bigger animal, will occasionally just swing her head around on its beautiful, stalklike neck and quietly begin to devour the male. He goes right on copulating, while she goes right on eating him. As long as the male's last two abdominal segments are left, they go on copulating.

Some years ago I visited my good friend, Professor Kenneth Roeder at Tufts College. When I got there and asked for him, a student told me, "You'll find Professor Roeder down that hall, last door on the right." So I went down, and there I found Ken Roeder sitting on a soap box watching praying mantises. He offered me another soap box and we sat there, watching together. He told me he had been doing this for years.

He told me that, if you've got a female mantis alone in a cage, and put in a male, that male instantly freezes. The praying mantis, like a lot of other animals, such as frogs, don't seem to be able to see anything unless it moves. The male knows that, and he's watching the female very carefully.

If she looks away for a moment, he takes a hasty few steps forward. Then he freezes again as soon as she looks back. Roeder said that this can go on for hours. If the male is fortunate, he reaches the female, mounts her, and goes through a normal copulation.

Incidentally, Roeder told me that once an American male mantis starts copulating, the female never bothers him. It's our better standard of living. But often the female sees him first. With that, she grabs him, always by the head. Then she begins to eat him, always starting with his head. As soon as she has eaten off the head, the male goes into a very interesting pattern of behavior. He plants his front feet squarely and begins to circle around them, meanwhile going through violent copulatory motions. In this way, Roeder told me, such a headless male will frequently succeed in mounting the female and going through a normal copulation.

Ken Roeder is a distinguished neurophysiologist. He was anxious to know what was going on here, and eventually worked that out. There is a copulatory center in the last abdominal segment. But there is an inhibitory center in the subesophageal ganglion that holds the copulatory center in check. It's all very simple. You don't need a female to remove this inhibition. Roeder used a razor blade to cut off the head. Once a male loses his head, the copulatory center is released. So here is an instance in which killing the male helps to stimulate the reproductive act.