In order to test my theory to the effect that the trap-door nests are enlarged from time to time, and that the numbers of layers of silk in an undisturbed cork door should represent the number of enlargements which the nest has undergone, I examined the doors of twenty-eight nests of the cork type (all I believe of N. cæmentaria), in order to prove whether as a rule the larger cork doors do contain more layers of silk than the small ones, as they should on this hypothesis.
This is, I think, fairly established by the following table:—
Comparative Table.
| One | cork | door | measuring | 1 | line | across contained | 1 | layer of silk. | |
| Four | " | doors | " | 1 | 1/2 | lines | " | 3 | layers " |
| One | " | door | " | 1 | 1/2 | " | 2 | " | |
| One | " | door | " | 1 | 3/4 | " | 4 | " | |
| One | " | door | " | 2 | " | 5 | " | ||
| Two | " | doors | " | 2 | 1/2 | " | 6 | " | |
| One | " | door | " | 2 | 1/2 | " | 5 | " | |
| One | " | door | " | 3 | " | 8 | " | ||
| Two | " | doors | " | 3 | 1/2 | " | 5 | " | |
| One | " | door | " | 3 | 1/2 | " | 7 | " | |
| One | " | door | " | 4 | " | 7 | " | ||
| Two | " | doors | " | 4 | 1/2 | " | 8 | " | |
| One | " | door | " | 4 | 1/2 | " | 7 | " | |
| Two | " | doors | " | 5 | " | 9 | " | ||
| One | " | door | " | 5 | " | 5 | " | ||
| One | " | door | " | 5 | " | 6 | " | ||
| One | " | door | " | 5 | " | 13 | " | ||
| One | " | door | " | 5 | 1/2 | " | 9 | " | |
| One | " | door | " | 5 | 1/2 | " | 10 | " | |
| One | " | door | " | 5 | 1/2 | " | 14 | " | |
| One | " | door | " | 6 | " | 12 | " |
The apparent exceptions to this rule, in which the larger doors have fewer layers than some of the smaller ones, may probably be accounted for in the following manner.
During the heavy rains and in times of drought flakes of earth often become detached from the sloping banks, and carry away the doors of such nests as are found in them.
This happens frequently, and the spiders hasten to repair the damage and spin new doors.
But I have found, on examining eight of these new doors, that, even in large nests,[107] they do not then contain more than three layers of silk; so that each time a nest of any size loses its door, the number of layers is greatly reduced.
[107] Of the eight doors in question the smallest measured 31/2 lines across, and the largest 7 lines.