formed in the spring by young queens, as worker wasps have not hatched at this time. While these worker wasps are growing in the nest, they are vulnerable to predators who might rip open the nest to eat the larva. One method the queens use to prevent this is covering the developing pupae in pulp, which acts as a reinforcer and makes it more difficult from predators to break open the pupae. This pulp is a mixture of plant matter and liquids from the mouth of the queen wasp. While there are costs associated with using pulp, such as requiring time and energy to collect materials and hindering the emergence of the worker wasps from the cocoon, it does lower the risk of predation. Nests in areas with higher predation rates have been found to contain more pulp on these cocoons than nests in low predation areas. Animals use the techniques of crypsis or camouflage, concealment, and mimicry, for avoiding detection. Some species of birds will use materials foraged from nature to camouflage their nests and prevent their offspring from being hunted. Blue–gray gnatcatchers (Polioptila caerulea) and long-tailed tits (Aegithalos caudatus) use materials such as spider webbing, silk, and lichen, while other species such as great crested flycatchers (Myiarchus crinitus) and common waxbills (Estrilda astrild) will use animal feces and snake skins to disguise their nests. Crypsis works by blending the structure with its background. The use of lichen flakes as an outer covering of nests by birds, as in the case of the paradise flycatcher (Terpsiphone paradisei) have been considered by some authors to be a case of crypsis through "branch-matching" and as a case of disruptive camouflage by the British ethologist, M. Hansell, where the lichen flakes are thought to resemble small patches of light seen through as in the case of insubstantial objects of insufficient importance to receive a predator's interest. Ground-nesting birds which rely on crypsis for concealment have nests made from local materials which blend in with the background, the eggs and young too are cryptic; whereas birds which do not use crypsis for hiding their nests may not have cryptic eggs or young. In a case apparently of masquerade, the red-faced spinetail Cranioleuca erythrops places bits of grass and other material loosely streaming both above and below the nest chamber to break the shape of the nest and to cause it to resemble random