This minute species may be found in large numbers nearly all the year round. Its larva is parasitic on a great variety of insects and is also not infrequently met with among decaying vegetable matter. Its habits are, therefore, very varied. When parasitic in the Lepidoptera it usually selects the noctuæ, destroying a great number of many of the commoner species[[14]]. The infected caterpillars usually turn into chrysalides some time before the little maggots emerge, but this is not invariably the case, the parasite often destroying the larva at a comparatively early stage. The pupæ are buried in the earth, near the remains of their host, and are light brown in colour, with the segments much more distinct than is usual (Fig. 15a). From these the perfect flies proceed in about a month's time. The occurrence of this insect as a parasite in Coleoptera is not common, but I know of one instance in which a number of these little flies were produced from a pupa of Uloma tenebrionides (Plate [II]., Figs. 2, 2a, 2b), which I was rearing at the time (page [29]). In this case it is difficult to understand how the female contrives to deposit her eggs in a horny beetle larva which lies safely hidden in its narrow tunnel in the middle of a large log of wood. Among bees this is a most destructive insect, its larva being parasitic in their grubs, and thus greatly reducing the population of the hive, which is finally ruined by the wholesale destruction of its honey when the flies emerge. Driving the bees into a fresh box would, no doubt, be frequently beneficial in these cases, but it is to be feared that bee-keepers will have much difficulty in contending with this insect. Its sexes are readily distinguished by their size, the female being considerably the larger.
Family Muscidæ.
Coelopa littoralis (Plate [VII]., fig. 13).
Extremely abundant on the sea-beach. Its larva feeds on decaying seaweed, burying itself in the sand before changing. The perfect insects often congregate in such vast numbers on some of the rocks that it is necessary to run past them in order to avoid being positively suffocated by the countless multitudes which fly up into one's face. This insect must be regarded as the New Zealand representative of the well-known dungfly of England (S. stercoraria), which many of my readers will recollect has a similar habit of assembling in great numbers.
Family Œstridæ.
Œstrus perplexus, n.s. (Plate [VII]., fig. 12).
This species is mentioned here as it is the only New Zealand exponent of a very important and well-known family of Dipterous insects. I am at present quite ignorant as to its life-history which would, no doubt, be very interesting. The only two specimens I possess were taken at Nelson, some four years back, so that it appears to be very rare.
The two remaining groups of the Diptera are of very limited extent. The Pupipara include a few anomalous species, in which the young are not deposited until they become pupæ, thus undergoing all their transformations within the body of the parent, while the Pulicina comprise the well-known fleas, which are probably identical with the European species. They are placed by many authors in a distinct order termed the Aphaniptera.
CHAPTER VI
