In the case of the common drone-fly, Eristalis tenax, the individual, from a sedentary maggot living in filth, without any relations of sex, and with only unimportant organs for the ingestion of its foul nutriment, changes to a creature of extreme alertness, with magnificent powers of flight, living on the products of the flowers it frequents, and endowed with highly complex sexual structures.
There is a common English Syrphid fly (Eristalis tenax) known as the drone-fly from its resemblance to a large hive or honey bee.
The particular likeness to a honey-bee presented by one member of this family, the drone-fly (Eristalis tenax), has been already referred to.
Other flies of the genus Volucella, larger and heavier in build than Eristalis, resemble humble-bees in colour and form, and it was formerly supposed that the purpose of this similarity was to enable the flies to enter with impunity the nests of the humble-bees and to lay their eggs amongst those of the latter insects.