The experiments of Ferton show us that the memory of the Osmias is facile, but, that it is not of the same degree in all species. A single exploration suffices Osmia rufohirta to learn to know well the new position of its shell; but several journeys are necessary for Osmia ferruginea to arrive at the same result.
The apprenticeship is rapid in the first species, slower in the second, but it is truly an apprenticeship. But the ability to learn plays a great part with the articulates and we must study it a little closer.
Let us consider first species which are lower in the entomological scale and for this purpose choose the orthopterous group Blattid (cockroaches). These insects are known to shun the light and to seek the darkest places. However, despite the very obvious repulsion which they show to light rays, one can teach cockroaches to endure them. It suffices to inflict on these insects when they wish to enter dark places a treatment which drives them away; an electric shock, for example. Szymanski (1912) and Turner (1912) have tried this method with the common cockroach (Blatta orientalis), which they submitted to shocks from an electric platform every time the insect wanted to go from the light chamber to the dark chamber of its cage. Each of these authors states that the common cockroach is very quick to learn, but different individuals are not equally apt. According to Szymanski, in order to make a blatta refuse ten times in succession to enter the light compartment, the number of shocks necessary varies from sixteen to one hundred and eighteen. Turner observes, moreover, that the males learn more quickly and remember better than the females, the young, or the aged individuals, and states that the habit may persist even after a molt. But is it really an acquired habit and not a phototropic reversal produced by the electricity! Turner has settled the question by trying apprenticeship of the blattas in a cage in which the two compartments (light and dark) had as a common partition, a curtain which did not quite reach the floor of the cage. Once the apprenticeship was completed, the same cockroaches were put into another cage where the common partition had a door. In this new lodging the insects went immediately to the dark compartment. They associated in this memory the sensations of shock with a certain place, but their repulsion from the light remained perfect.
Certain Coleoptera are equally teachable, among others the margined Dytiscus, which is a large fresh-water beetle. Forel says (1900) :
A Dytiscus marginalis which I had in a bowl, and which I was accustomed to eed, ended by learning a little. Instead of retreating to the bottom of the bowl when I entered, it jumped almost out of the water and immediately seized what I gave it, even from my finger. Quiet before, it put itself in motion as soon as it saw me enter. It remembered then that it was I (I don't believe that it could distinguish me from another person) who brought it food.
Labitte has also noticed an apprenticeship with the same insect.
The yellow-winged sphex (Sphex flavipennis) is a hunter of crickets, which digs its nest, a nest with several cells, before leaving on a provisioning expedition. "When it returns with its burden, it drops it near the entrance of the burrow, makes a domiciliary visit, then comes out to seize its benumbed victim, which it drags in by the antennae This wasp forms little colonies of from ten to twelve individuals in sandy soil. Fabre tried the following experiment on a wasp of one of these colonies : While one of them was making its domiciliary visit, he removed the victim to some distance, which caused a search by the wasp on issuing. Once in possession of its prey, the sphex dragged it to the edge of the burrow and again left it, to explore the hole again. More than twenty successive times Fabre repeated the process. The wasp never failed to bring the cricket back to the nest and to leave it there, to make its visit. All the wasps of the colony behaved in the same way, and not only these but those which nested in the same place the next year and which were the descendants of the first, But the wasps of another colony were not so foolish: after two or three times they learned to avoid the trick and, without any visit, they dragged the cricket into the burrow. "Thus," concludes Fabre, "the knowledge of the trick is transmitted; there are tribes that are more clever and those that are more simple, apparently according to the faculties of their fathers." The insect does not always obey "a fatal inclination which circumstances cannot modify," its acts are not "invariable," and it is wrong to believe it incapable "of acquiring the least experience at its own expense. ' '
According to Nicolas, Pompilus viaticus is no less wise. Like all the Pompilid, it is a hunter of spiders; but instead of storing its victim immediately, after the manner of the other species of the same genus, it leaves it near the burrow, to make a domiciliary visit. If the spider is removed a little way during the visit, it does not fail to bring it back and to enter its burrow immediately ; but it does not act this way long, for if the same trick is tried several times, it enters direct with its victim.
The social Hymenoptera,-wasps, bees, and ants,-learn and retain with more facility. We shall see in other parts of this book with what facility Lubbock, Forel, and many others knew how to accustom them to come to take honey from fixed places, and how they came to those places even when the honey was no longer there. François Huber1 cites a characteristic observation on this subject :
Some honey had been placed on a window ledge in the autumn, and the bees came in crowds. The honey was taken away and the window was closed all winter. The following spring when the window was opened the bees returned, although there was no longer any honey there. . . . An interval of several months had not effaced the impression.
Lovell (1909) reports a similar observation and all bee-keepers know that bees retain for a long time the memory of places where they have found honey.
Articulates other than insects also are capable of changing their habits by apprenticeship. Placing American crawfish in a boat with two gangways, the one covered with glass and the other open, Yerkes and Huggins (1902) accustomed the animals to avoid the former and to use the latter. It took a month and sixty trials to attain this result. Progress was slow but continuous and the habit persisted fifteen days after the education. It took an equal amount of patience for Drzewina (1910) to accustom a Gulf of Biscay crab (Grapsus varius) to use a side door made in the glass partition which divided its boat into two compartments. The crabs of this species wish to go in a straight line toward the sources of light. Drzewina's crab was attracted toward the empty compartment by the light of a candle; on the way it met the glass partition and, in its effort to find a way through, finally found the door ; and the many trials taught it finally to go straight to the door.
1 F. Huber, Nouvelles observations sur les Abeilles, 1814.