632 



AN INTRODUCTION TO ENTOMOLOGY 



and the outer layers have the threads arranged so as to form a 

 beautiful openwork pattern. The adult moth has a wing-expanse of 

 about 12 mm. It is figured by Slingerland and 

 Crosby ('14). _ 



The suspended lace-cocoon, Urodus pdrvula. — 

 This beautiful cocoon (Fig. 773) is not uncommon 

 in Florida. It is found in various situations. I 

 found the specimen figured here attached to an 

 orange leaf. The adult is a brownish moth without 

 markings and with a wing-expanse of 28 mm. 



The ailanthus webworm, Atteva atirea. — The lar- 

 vae live in communities within a slight silken web 

 on the Ailanthus; they feed on the leaves and also 

 gnaw the leaf -stalks in two. When the larva is full- 

 grown it suspends itself in the middle of a loose web 

 and transforms there. The adults appear in Sep- 

 tember and October and pass the winter in this state. 

 The adult is very striking in appearance. The fore 

 wings are bright marigold -yellow with four bands of 

 round pale sulphur-yellow spots upon a brilliant 

 steel-blue ground. The hind wings are transparent, 

 with a dusky margin and blackish veins. The wing- 

 expanse is about 25 mm. 

 The ermine-moths, Yponomeiita. — There are several species of 

 the typical genus of this family that have received the common name 

 ermine-moths, because of the color of their fore wings, which are 

 snowy white dotted with black. One of these, Yponomeiita padella, 

 is an introduced species which is an apple and cherry pest. The 

 larvae live in a common web, and in this they spin their cocoons. 

 The name ermine-moths is applied also, especially in England, to 

 some of the Arctiidce that are white spotted with black. 



Fig- 773-— Co- 

 coon of Uro- 

 dus parvtila 



Family PLUTELLID^ 



This family is closely allied to the Yponomeutidae and is regarded 

 by many writers as a subfamily of that family. These moths differ 

 from the Yponomeutidae in that they hold the antennae extended 

 forward in repose; in this respect they resemble the Coleophoridas. 

 The larvae differ from those of the Yponomeutidae and the Scj^thrididas 

 in that their prolegs are longer than wide. 



About fifty North American species have been described; these 

 represent nine genera. The most important species from an economic 

 standpoint is the following one. 



The diamond-back moth, Plutella maculipennis. — The larva of this 

 species infests cabbage and other cruciferous plants, eating holes of 

 variable size and irregular form in the leaves. It is sometimes also 

 a pest in greenhouses, infesting stocks, wall-fiowers, sweet alyssum, 

 and candytuft. The larva when full-grown spins a lace-like cocoon 

 attached to a leaf. The moth expands about 1 5 mm. The fore wings 



