Everything is to be hermetically sealed.
The mason-fly commences by flattening the first pill of clay upon the intended site (say the corner of a room); she then spreads it in a thin layer over a surface of about two inches, and retires for another ball of clay.

This she dabs upon the plastic foundation, and continues the apparently rude operation until some twenty or thirty pills of clay are adhering at equal distances.

She then forms these into a number of neat oval-shaped cells, about the size of a wren's egg, and in each cell she deposits one egg.

She then flies off in search of spiders, which are to be laid tip in stores within the cells as food for the young larvae, when hatched.
Now the transition from the larva to the fly takes place in the cell, and occupies about six weeks from the time the egg is first laid; thus, as the egg itself is not vivified for some weeks after it is deposited, the spiders have to be preserved in a sound and fresh state during that interval until the larva is in such an advanced stage as to require food.
In a tropical country every one knows that a very few hours occasion the putrefaction of all dead animal substances; nevertheless these spiders are to be kept fresh and good, like our tins of preserved meats, to be eaten when required.
One, two, or even three spiders, according to their size, the mason-fly deposits in each cell, and then closes it hermetically with clay.

The spiders she has pounced upon while sunning themselves in the centre of their delicate nets, and they are hurried off in a panic to be converted into preserved provisions.