XVI. The structure and life-history of the Holly-fly. 
By Proressor L. C. Mraz, F.R.S., and T. H. 
TAYLOR. 
[Read March 20th, 1907.] 
I. INTRODUCTION. 
Occurrence.—Holly-leaves are often infested by a small 
Dipterous larva, which forms discoloured blisters upon 
them. When opened with a needle the blisters are found 
to contain yellowish-white larve with black heads and 
tails. In particular localities a large proportion of the 
leaves may be disfigured in this way, and it was the 
abundance of the insect near Leeds which caused us to 
undertake its investigation. 
Goureau * has published a slight notice of the holly-fly, 
to which he gave the name of Phytomyza aquifolu. We 
have not attended to the classification of Phytomyza, and 
express no opinion upon the validity of the species.+ 
Summary of Lrfe-history—The life of the holly-fly 
occupies about a year, and extends from one June to the 
next. In June the young leaves of the tree are expanding, 
and the eggs are laid in the midrib while it is still tender. 
The larva soon hatches out, and remains in the midrib for 
about two months, boring its way along the central vessel 
(fig. 1). Then it turns aside, and enters the blade of the 
leaf, feeding on the green cells beneath the upper epidermis, 
and producing a blister of irregular shape, which at first 
takes a pale colour in consequence of the contained air. 
More than one larva may attack the same leaf, and their 
blisters sometimes run together. The cuticle is too opaque 
for the larva to show through it, but it can be felt by 
gentle pressure with the finger-tip. When feeding it lies 
on either its right or left side, and mows down the cells 
with its mouth-hooks, leaving a track which, while fresh, 
is visible from without, and reminds one of the path made 
* Ann. Soc. Ent. France, vol. ii, p. 143 (1851). 
t+ There is a brief notice of the holly-fly in Réaumur’s “ Histoire 
des Insectes,” vol. 111, mém. 1 (1737). 
TRANS, ENT. SOC. LOND. 1907.—PART I. (SEPT.) 
