Buprestis splendens. A living individual was removed from a desk which had stood in a London counting-house for thirty years; from the condition of the wood it was evident that the larva had been in it before the desk was made[[16]].
Blaps mortisaga. One individual lived three months, and two others three years.
Blaps fatidica. One individual which was left in a box and forgotten, was found alive when the box was opened six years afterwards.
Blaps obtusa. One lived a year and a half in confinement.
Eleodes grandis and E. dentipes. Eight of these beetles from California were kept in confinement and without food for two years by Dr. Gissler, of Brooklyn; they were then sent to Dr. Hagen who kept them another year.
Goliathus cacicus. One individual lived in a hot-house for five months.
In addition to these cases, Dr. Hagen writes to me: ‘Among the beetles which live for more than a year,—Blaps, Pasimachus, (Carabidae)—and among ants, almost thirty per cent. are found with the cuticle worn out and cracked, and the powerful mandibles so greatly worn down that species were formerly founded upon this point. The mandibles are sometimes worn down to the hypodermis.’
From the data before me I am inclined to believe that in certain beetles the normal length of life extends over some years, and this is especially the case with the Blapidae. It seems probable that in these cases another factor is present,—a vita minima, or apparent death, a sinking of the vital processes to a minimum in consequence of starvation, which we might call the hunger sleep, after the analogy of winter sleep. The winter sleep is usually ascribed to cold alone, and some insects certainly become so torpid that they appear to be dead when the temperature is low. But cold does not affect all insects in this way. Among bees, for example, the activity of the insects diminishes to a marked extent at the beginning of winter, but if the temperature continues to fall, they become active again, run about, and as the bee-keepers say, ‘try to warm themselves by exercise’; by this means they keep some life in them. If the frost is very severe, they die. In the tropics the period of hibernation for many animals coincides with the time of maximum heat and drought. This shows that the organism can be brought into the condition of a vita minima in various ways, and it would not be at all remarkable if such a state were induced in certain insects by hunger. Exact experiments however are the only means by which such a suggestion can be tested, and I have already commenced a series of experiments. The fact that certain beetles live without food for many years (even six) can hardly be explained on any other supposition, for these insects consume a fair amount of food under normal conditions, and it is inconceivable that they could live for years without food, if the metabolism were carried on with its usual energy.
A very striking example, showing that longevity may be induced by the lengthening of the period of reproductive activity, is communicated to me by Dr. Adler in the following note: ‘Three years ago I accidentally noticed that ovoviviparous development takes place in Chrysomela varians,—a fact which I afterwards discovered had been already described by another entomologist.
‘The egg passes through all the developmental stages in the ovary; when these are completed the egg is laid, and a minute or two afterwards the larva breaks through the egg-shell. In each division of the ovary the eggs undergo development one at a time; it therefore follows that they are laid at considerable intervals, so that a long life becomes necessary in order to ensure the development of a sufficiently long series of eggs. Hence it comes about that the females live a full year. Among other species of Chrysomela two generations succeed each other in a year, and the duration of life in the individual varies from a few months to half a year.’