Chapter 15. 
INJURIOUS INSECTS (Continued). 
Crane Flies; the Pear Midge; the Celery Fly; the Cabbage 
Root Fly; the Onion Fly; the Narcissus Fly; the House Fly. 
In this lecture we are concerned with the order Diptera 
which comprises the true Flies. These Insects can be 
recognised by the presence of a single pair of wings, the 
hinder pair being absent, and only represented by curious 
knobbed organs known as halteres or balancers. The 
larva of the Diptera are devoid of true limbs and are 
‘commonly known as maggots. A pupa stage is always 
present and, in a very large number of species, the skin 
of the larva is retained, forming a hardened case or 
puparium enclosing the true pupa. Although no adult 
Flies are directly injurious to vegetation, certain kinds 
such as Mosquitoes, Sand Flies, and Tsetse Flies are 
injurious to man. They pierce the skin in order to suck 
his blood and thereby act as carriers of the organisms of 
some of the most virulent diseases. 
Some of the most familiar of the larger Flies are the 
“Daddy Long Legs,” or Crane Flies (Zzgula oleracea and 
allied species) (13). Although they are commonly pests 
of our meadows and cereal crops nevertheless they not in- 
frequently injure turnips, peas, beans, cabbages, hops, 
dahlias, carnations and other garden plants. Their larve 
are commonly known as “ leather jackets,” and when fully 
grown they attain a length of 1$in. In colour they are 
dull grey or brown and are not unlike fragments of small 
113 
