62 



INSECTS. 



Hover-Flies. 



the young are retained within the parent's body, and nourished at its expense until 

 the pupa stage is reached. The flies of the last category are for this reason 

 generally called Pupipara. 



The family Syrphidce includes a number of species which, 

 although differing considerably in external form, may be distinguished 

 from other members of the suborder by the presence of the so-called spurious vein 

 in the wing — a vein lying between the third and fourth longitudinal veins, and 



crossing the short transverse vein (marked in 

 the figure on p. 48) which unites them. They 

 also bear considerable superficial resemblance, 

 both in colour and shape, to various bees and 

 wasps. The best known types are the hover- 

 flies (Syrphus), drone - flies ( Eristalis), and 

 humble-bee flies (Volucella). The hover -flies 

 of the genus Syrphus, which with their black 

 and yellow bands mimic wasps, are so named on 

 account of their habit of hovering in flower- 

 gardens in summer, darting from blossom to 

 blossom, and often sustaining themselves poised 

 in mid-air, after the manner of a hawk. The 

 females lay their eggs singly on leaves and 

 stems infested with plant-lice ; and the larvae 

 devour numbers of these pests, seizing them in 

 a most voracious manner, sucking them dry, and 

 rejecting the empty skins. 



Like the hover - flies, drone- 

 flies {Eristalis) frequent flower- 

 gardens, where they may be seen in numbers on 

 various blossoms. As their name indicates, these 

 flies resemble honey-bees, the likeness being so 

 close that it is difficult to persuade an uninitiated 

 person that they may be handled with impunity. 

 The resemblance, which is enhanced by the 

 ceaseless twitching of the abdomen, appears 

 indeed to be more deeply seated than might at 

 first be supposed, for spiders, which recognise their prey by touch and not by sight, 

 treat the drone-flies with caution. Thus a blue-bottle fly placed in a web of the 

 field-spider was immediately and without hesitation seized and devoured, although 

 a humble-bee was avoided by the spider, which — evidently fearing to come to close 

 quarters — let out a thread, and rushing round and round its victim at a distance, 

 succeeded in winding it up, and then approaching, inflicted a bite which soon put 

 an end to the insect's struggles. When a drone-fly was thrown into the web, the 

 spider darted at it as before, but as soon as it touched the fly with its fore-legs, 

 recoiled, as if in alarm, then returning to the attack dealt with the harmless 

 victim just as it had previously acted with the humble-bee. The larva? of the 

 drone-flies live mainly in ditches and feed upon decaying organic matter, and are 



Drone-Flies. 



hover-fly (Syrphus seleniticus). 

 1, Fly ; 2, Fly hovering ; 3, Larvae devouring 

 plant-lice on leaf ; 4, Larva ; 5, 6, Differ- 

 ent views of pupa. (4, 5, 6, enlarged ; 

 the rest nat. size. ) 



