THERE are, of course, examples of social life, or a tendency towards it, in other animals besides man, such as in wolves, for instance, hunting in packs; in beavers living in communities; and in the baboon community on the Rock of Gibraltar. There are also other social, or partly social, insects besides the four families before-mentioned. Examples are the bark-beetles, lady-birds in hibernation, and also some tropical spiders. It is evident that evolution has taken a very long time to produce the insects who lead a permanent social life and it is also clear that they are descended from solitary forms.
Wheeler has given a series of seven stages by which social life may have been built up, and the series may be quoted with advantage here:
1. The insect mother merely scatters her eggs in the general environment in which the individuals of her species normally live. In some cases the eggs are placed near the larval food.
2. She places her eggs on some portion of the environment (leaves, etc.) which will serve as food for the hatching larvas.
3. She supplies her eggs with a protective covering. This stage may be combined with (1) or (2).
4. She remains with her eggs and young larvas and protects them.
5. She deposits her eggs in a safe or specially prepared situation (nest) with a supply of food easily accessible to the hatching young (mass provisioning).
6. She remains with the eggs and young and protects and continuously feeds the latter with prepared food (progressive provisioning).
7. The progeny are not only protected and fed by the mother, but eventually co-operate with her in rearing additional broods of young, so that parent and offspring live together in an annual or perennial society.
Having reached this stage, let us consider some of the many interesting problems to be found among the social insects. For this purpose we will take the wasps first; next, the ants, about which, perhaps, the most is known, and on which the most work has been accomplished; and then we will consider the termites.
THE WASP COLONY AND ITS GUESTS
THE social wasps themselves have been evolved from various primitive solitary wasps. One of the most striking phenomena which wasps possess in common with ants is the mutual exchange of food between the mature wasps and their grubs. This can be more easily observed in wasps kept in captivity than in other social insects.
After a worker wasp has given chewed-up pieces of insects to the grubs, she then imbibes drops of a saccharine liquid which the grubs let fall from their mouths. Sometimes, however, she demands this secretion when the grubs have not been fed, and should the latter not respond at once, she will gently bite their heads to force them to produce this salivary fluid.
Both male and queen wasps are very fond of this secretion; in fact, the larva; appear to be rather exploited, often having to give more nutriment than they receive, and this has been said to help to produce the worker caste, that is, imperfectly developed females.
THE WASP AND THE HONEY-POT: AN EPIC OF PERSEVERANCE w
ASPS devour a quantity of insects, but are also fond of sweets, nectar from flowers and honey. They can be seen to eat a little meat in butchers’ shops, but they are useful to the butchers, as they catch ‘blue-botdes,’ cutting off their heads and wings and flying away with their spoils back to their nest. They have a very good memory and will fly long distances from the nest in search of food and chewed wood which they scrape off posts and trees, to make the paper with which they construct the nest. The present writer made observations on a wasp which visited his study for ten days to obtain honey from a pot kept on his table for the benefit of his ants.
Whilst writing at the study table, he noticed a worker wasp, which had.come in at the window, hovering over and flying down into the small jug containing the honey. Only a small quantity of honey was left at the bottom of the jug, and the wasp had to go right down to the bottom to get at it. It was found that the wasp came back on and off to the honey, so the writer determined to put down the times of its arrivals and departures. It was found to come regularly from August 22nd to September 9th, after which date it was seen no more.
It started coming as soon as the study window was opened in the morning. Seven thirty a.m. was the earliest time noted, and seven-thirty-six p.m. was the latest departure before the window was shut. The time the wasp spent at the honey varied considerably, but the time between its departures and its return was mostly about seven minutes. It was very nervous at first, and the least jar of the table, or a shadow cast over the honey-pot, caused it to fly off; but eventually it got quite tame and did not fly away even when the honey-pot was moved about.
When it left the honey, it flew straight out of the window across the garden, and over some trees at the bottom of the garden, but when returning, it was more deliberate, entering the window with a ‘buzz ‘and circling over the honey-pot before dropping into it. In the morning it was generally waiting outside for the window to be opened, when it entered
THE WASP COLONY AND ITS GUESTS
at once; and on several occasions it continued to come during heavy rains. The following is the time-table kept for one day, which shows the wonderful industry and the perseverance of the brave little creature.
Arrival Departure Arrival Departure
7.43 a.m. 7-55 a.m. 2.26 p.m. 2.37 p.m.
8. 8. 2. 2.54
9- 9- 3- 3.10
9. 9- 3- 3-28
io- iQ-4- 4.20
‘• n- 5- 5.26
11.12.3 p.m. 5- 5-45
12.11 p.m. 12.5- 6-5
12.1. 6. 6.42
1. 1. 6. 6-59
1. 7- 7.16
2. 2. 7- 7-36
Where there is a long interval in the records, the observer was either out of the room or at meals.
Colonies of the chief social wasps are each started by one fertile female which has passed the winter in hibernation. In the spring she starts a small nest of a few cells made from the paper mentioned above and lays eggs in them. The nests may be built in the ground, in hollow trees, or hanging on branches. When the workers hatch, they help to increase the size of the nest and to bring up the brood. Later in the summer, males and females are brought up, and, after mating has taken place, which is generally late in the year (we have noticed it as late as November), the whole colony perishes, except for the fecundated females which go into hibernation.
WASPS WHICH TAKE IN YOUNG BOARDERS DURING their journeys after food, wasps must come in contact with many different organisms and surroundings; but in their nests, they also become associated with other creatures which seek out these nests and live with their inmates as scavengers, messmates, or parasites. There are two parasitic species among the social wasps which have lost the worker
caste, and their males and fertile females live in the nests of wasps which possess workers. The latter feed them, and bring up their brood, treating them in the same way as they do their own. Some small beetles which live in wasps’ nests and feed upon the paper and debris in them are confined to special types of nests. Thus one species only occurs in nests in the ground; another in the nests of wasps and hornets built in trees.
The large rove beetle, which bears a superficial resemblance to the well-known ‘Devil’s coach-horse,’ lives in hornets’ nests, where it lays its eggs and where its larvas are bred. It is not harmful to the hornets, as its larva: feed on rcjcctmenta, dead hornet grubs and other refuse in the nest. It is nocturnal in its habits, and, with the aid of a dark lantern, the writer has seen it at night fly to and enter a hole in a hollow birch tree inhabited by a colony of hornets.
There is a bright metallic blue tropical species which lives a similar life in the nests of a small but populous species of bee. One of the parasites lays its eggs in wasp grubs, and its larva hatches in the grub’s body. It is careful not to destroy the wasp grub until the latter has assumed the pupal state. Then it devours the hind body of the pupa completely, and makes a cocoon in its place at the bottom of the cell which contained the wasp grub. It leaves the head and thorax of the grub, which retain their shape but present a rather ghostly appearance as a lump of colourless jelly.
There are certain fly larvaj, some of which are covered with spines, which act as scavengers in wasps’ nests. The perfect fly of one of these, which is not unlike a honey-bee superficially, boldly enters its hosts’ nest to lay its eggs. Its larvae are bred in the debris at the bottom of the nest.