“As the _Stylops_ emerges from the body of the bee, the latter seems to suffer from much irritating excitement.”
Mr. Thwaites writes to me, on the 12th May, thus: “I had the good fortune to capture a _Stylops_ flying, and on the Tuesday following saw at least twenty flying about in the garden, but so high from the ground that I could capture only about half-a-dozen; since that time they have become gradually more scarce.
“The little animals are exceedingly graceful in their flight, taking long sweeps as if carried along by a gentle breeze, and occasionally hovering at a few inches distance from the ground. Their expanse of wing and mode of flight give them a very different appearance to any other insect on the wing. When captured they are exceedingly active, running up and down the sides of the bottle in which they are confined, moving their wings and antennæ very rapidly. Their term of life seems to be very short, none of those I have captured living beyond five hours, and one I extracted from a bee in the afternoon was dead the next morning.
“All the bees stylopized, both male and female, I have taken, have manifested it by having underneath the fourth (invariably) upper segment of the abdomen a protuberance which is scale-like when the _Stylops_ is in the larva state; but which is much larger and more rounded when the _Stylops_ is ready to emerge. A bee gives nourishment generally to but one _Stylops_; but I have occasionally found two, and once three larvæ in one bee.”
The structure of these insects is very remarkable: the typical genus _Stylops_ is named from its compound eyes, which consist of a very few (about fifteen) hexagonal facets, seated upon a sort of footstalk. The mandibles are lancet-shaped and very acute, and the head, by reason of the protuberant eyes, has very much the shape of a dumb-bell. The antennæ are branched, but in _Halictophagus_, they are flabellate. The thorax is greatly developed; the superior wing is like a rudimentary wing-case, and is twisted, the inferior wings are very large, and fold along the abdomen in repose like a fan; the legs are slender, and the tarsi with four joints in _Stylops_, with three in _Halictophagus_, and with two in _Elenchus_; the abdomen is long, very flexible, and consists of eight segments. The insects themselves do not exceed a quarter of an inch in length in the largest, but they are generally very much smaller. The perfect insect is very short-lived, not surviving many hours, as just stated. They are usually found in the months of May and June, and they have been discovered to infest several species of _Andrena_ and _Halictus_, for instance the _A. nigro-ænea_, upon which Mr. Kirby first found it; _A. labialis_, which I have frequently caught stylopized; _A. rufitarsis_, _fulvicrus_, _Mouffetella_, _tibialis_, _Collinsonana_, _varians_, _picicornis_, _nana_, _parvula_, _xanthura_, _convexiuscula_, _Afzeliella_, _Gwynana_, etc., and upon _Halictus æratus_, etc.