WEST AFRICAN TEYPETlDiE. 165 



Dacus, Fabricius. 



Wasp-like flies measuring :f to | inch long. 



The body is usually brown or black with canary-yellow spots and lines ; 

 the wings clear, with usually, in West African species, two brown bands 

 starting from the base of the wing : a broader band extending along the 

 anterior margin, and a narrower one crossing the wing from the base at an 

 oblique angle and ending at the posterior border. 



In life the eyes are purple with dull green reflections. In dried specimens 

 they become a dark purple-brown ; and the scutellum, with the spots and 

 lines upon the thorax, which in life are a canary-yellow, often become orange 

 or brown, and the fine yellow lines almost disappear. The wasp-like appear- 

 ance, caused by the spheroidal shape of the abdomen with its ontracted waist 

 and by the brown and yellow coloration, together with the clear wings, which 

 are usually banded along the costa (front edge of wing), and the peculiar size 

 and shape of the 2nd basal cell, should enable the flies of this genus to be 

 readily recognised. 



The habits of only two of the West African species are known. The 

 females of i). hipartitus and V, vertehratus -mixy be found, singly or in groups 

 of 3 or 4, walking about upon the surface of young melons or vegetable 

 marrows. Suddenly a fly ceases walking and remains stationary in one spot. 

 If killed she will, be found to have inserted her ovipositor through the skin 

 of the fruit and deposited a little pile of eggs VN^thin. The eggs hatch into 

 yellowish-W'hite elongated maggots, which burrow in the pulp and grow until 

 they are 10-11 mm. long by 2*5 mm. broad. Their presence causes the 

 melon to rot/ and the decay gradually extends outwards until it reaches the 

 skin, appearing as a yellow area. Through the rotten portion, or upon the 

 bursting of. the fruit, the larva3 escape ; they leap about upon the ground for 

 a minute or two and then rapidly bury themselves, beyond the remains of 

 the rotten fruit, a couple of inches deep in the ground. Here they enter 

 the pupal stage. The pupa is an egg-shaped pale yellow body measuring 

 6*5 mm. long by 3 mm. brxxid.. After about 15-16 days the flies leave the 

 pupa-cases, make their way to the surface of the ground, expand and dry 

 their wings, and fly aw^ay to repeat the process in another melon. The power 

 of leaping possessed by the maggots is considerable and enables them to leap 

 over the cordon of ants which is generally drawn round the rotten fruit. 

 The advantage of this capacity for jumping is well seen by dropping a 

 maggot among ants. Though at once attacked by the ants it usually 

 manages to get rid of its assailants by a few violent leaps. The power 

 may also be useful in enabling the larva rapidly to reach ground which is 

 uncontaminated by the fruit-juices, for such contamination favours the growth 

 of moulds, some of which may cause the death of the pupa. 



