THE PARASITES OF THE HONEY BEE.
Very few bee-keepers are probably aware how many insect parasites infest
the Honey bee. In our own literature we hear almost nothing of this
subject, but in Europe much has been written on bee parasites. From Dr.
Edward Assmuss' little work on the "Parasites of the Honey Bee," we
glean some of the facts now presented, and which cannot fail to interest
the general reader as well as the owner of bees.
The study of the habits of animal parasites has of late gained much
attention among naturalists, and both the honey and wild bees afford
good examples of the singular relation between the host and the
parasites which live upon it. Among insects generally, there are certain
species which devour the contents of the egg of the victim. Others, and
this is the most common mode of parasitism, attack the insect in its
larva state; others, in the pupa state, and still others in the perfect,
or imago state. Dr. Leidy has shown that the wood-devouring species of
beetle, Passalus cornutus, and some Myriopods, or "thousand legs," are,
in some cases, tenanted by myriads of microscopic plants and worms which
luxuriate in the alimentary canal, while the "caterpillar-fungus"
attacks sickly caterpillars, filling out their bodies, and sending out
shoots into the air, so that the insect looks as if transformed into a
vegetable.
The Ichneumon flies, of which there are undoubtedly several thousand
species in this country, are the most common insect parasites. Next to
these are the different species of Tachina and its allied genera. These,
like Ichneumons, live in the bodies of their hosts, consuming the fatty
parts, and finishing their transformations just as the exhausted host
is ready to die, issue from their bodies as flies, closely resembling
the common housefly.
A small fly has been found in Europe to be the most formidable foe of
the hive bee, sometimes producing the well-known disease called
"foul-brood," which is analogous to the typhus fever of man.
[Illustration: 32. Phora and its Young.]
This fly, belonging to the genus Phora (Fig. 32, Phora incrassata; _a_,
larva; _b_, puparium; _c_, another species from Mammoth Cave), is a
small insect about a line and a half long, and found in Europe during
the summer and autumn flying slowly about flowers and windows, and in
the vicinity of beehives. Its white, transparent larva is cylindrical, a
little pointed before, but broader behind. The head is small and
rounded, with short, three-jointed antennæ, and at the posterior end of
the body are several slender spines. The puparium, or pupa case,
inclosing the delicate chrysalis, is oval, consisting of eight segments,
flattened above, with two large spines near the head, and four on the
extremity of the body.
When impelled by instinct to provide for the continuance of its species,
the Phora enters the beehive and gains admission to a cell, when it
bores with its ovipositor through the skin of the bee larva, laying its
long oval egg in a horizontal position just under the skin. The embryo
of the Phora is already well developed, so that in three hours after the
egg is inserted in the body of its unsuspecting and helpless host, the
embryo is nearly ready to hatch. In about two hours more it actually
breaks off the larger end of the egg-shell and at once begins to eat the
fatty tissues of its victim, its posterior half still remaining in the
shell. In an hour more, it leaves the egg entirely and buries itself
completely in the fatty portion of the young bee.
The maggot moults three times. In twelve hours after the last moult it
turns around with its head towards the posterior end of the body of its
host, and in another twelve hours, having become full-fed, it bores
through the skin of the young, eats its way through the brood-covering
of the cell and falls to the bottom of the hive, where it changes to a
pupa in the dust and dirt, or else creeps out of the door and transforms
in the earth. Twelve days after, the fly appears.
The young bee, emaciated and enfeebled by the attacks of its ravenous
parasite, dies, and its decaying body fills the bottom of the cell with
a slimy, foul-smelling mass, called "foul-brood." This gives rise to a
miasma which poisons the neighboring brood, until the contagion (for the
disease is analogous to typhus, jail or ship-fever) spreads through the
whole hive, unless promptly checked by removing the cause and thoroughly
cleansing the hive.
Foul-brood sometimes attacks our American hives, and, though the cause
may not be known, yet from the hints given above we hope to have the
history of our species of Phora cleared up, should our disease be found
to be sometimes due to the attacks of such a parasitic fly.
[Illustration: 33. Bee Louse and Larva.]
We figure the Bee louse of Europe (Fig. 33 b, Braula cæca), which is a
singular wingless spider-like fly, allied to the wingless Sheep tick
(Melophagus), the wingless Bat tick (Nycteribia) and the winged Horse
fly (Hippobosca). The head is very large, without eyes or ocelli (simple
eyes), while the ovate hind-body consists of five segments, and is
covered with stiff hairs. It is one-half to two-thirds of a line long.
This spider fly is "pupiparous," that is, the young, of which only a
very few are produced, is not born until it has assumed the pupa state
or is just about to do so. The larva (Fig. 33 _a_) is oval,
eleven-jointed, and white in color. The very day it is hatched, it sheds
its skin and changes to an oval puparium of a dark brown color.
Its habits resemble those of the flea. Indeed, should we compress its
body strongly, it would bear a striking resemblance to that insect. It
is evidently a connecting link between the flea, and the two winged
flies. Like the former it lives on the body of its host, and obtains its
food by plunging its stout beak into the bee and sucking its blood.
It has not been noticed in this country, but is liable to be imported on
the bodies of Italian bees. Generally, one or two of the Braulas may, on
close examination, be detected on the body of the bee; sometimes the
poor bees are loaded down by as many as a hundred of these hungry
blood-suckers. Assmuss recommends rubbing them off with a feather, as
the bee goes in and out of the door of its hive.
[Illustration: 34. Hive Trichodes.]
Among the beetles are a few forms occasionally found in bees' nests and
also parasitic on the body of the bee. Trichodes apiarius (Fig. 34, _a_,
larva; _b_, pupa, front view) has long been known in Europe to attack
the young bees. In its perfect, or beetle state it is found on flowers,
like our Trichodes Nuttallii, which is commonly found on the Spiræa in
August, and which may yet prove to enter our beehives. The larva devours
the brood, but with the modern hive its ravages may be readily detected.
[Illustration: 35. Meloë.]
The Oil beetle, Meloë angusticollis (Fig. 35, male, differing from the
female by having the antennæ as if twisted into a knot; Fig. 36, the
active larva found on the body of the bee), is a large dark blue insect
found crawling in the grass in the vicinity of the nests of Andrena,
Halictus, and other wild bees in May, and again in August and
September. The eggs are laid in a mass covered with earth at the root
of some plant. During April and early in May, when the willows are in
blossom, we have found the young recently hatched larvæ in considerable
abundance creeping briskly over the bees, or with their heads plunged
between the segments of the body, greedily sucking in the juices of
their host. Those that we saw occurred on the Humble and other wild
bees, and on various flies (Syrphus and Muscidæ), and there is no reason
why they should not infest the Honey bee, which frequents similar
flowers, as they are actually known to do in Europe. These larvæ are
probably hatched out near where the bees hibernate, so as to creep into
their bodies before they fly in the spring, as it would be impossible
for them to crawl up a willow tree ten feet high or more, their feet
being solely adapted for climbing over the hairy body of the bee, which
they do not leave until about to undergo their strange and unusual
transformations.
[Illustration: Early Stages of Meloë.]
In Europe, Assmuss states that on being brought into the nest by the
bee, they leave the bee and devour the eggs in the bee cells, and then
attack the bee bread. When full-fed and ready to pass through their
transformations to attain the beetle state, instead of at once assuming
the pupa and imago forms, as in the Trichodes represented in fig. 34,
they pass through a _hyper-metamorphosis_, as Fabre, a French
naturalist, calls it. In other words, the changes in form which are
preparatory to assuming the pupa and imago states are more marked and
almost coequal with the larva and pupa states, so that the Meloë,
instead of passing through three states (the egg, larva and pupa), in
realty passes through these and two others in addition, which are
intermediate. The whole subject of the metamorphosis of this beetle
needs revision, but Fabre states that the larva, soon after entering the
nest of its host, changes its skin and assumes a second larva form.
Newport, who with Siebold has carefully described the metamorphoses of
Meloë, does not mention this stage in its development, which Fabre calls
"pseudo-chrysalis." It is motionless, the head is mask-like, without
movable appendages, and the feet are represented by six tubercles. This
is more properly speaking the semi-pupa, and the mature pupa grows
beneath its mask-like form, which is finally moulted. This form,
however, according to Fabre, changes its skin and turns into a third
larva form (Fig. 37). After some time it assumes its true pupa form
(Fig. 38), and finally moults this skin to appear as a beetle.
Fabre has also, in a lively and well-written account, given a history of
Sitaris, a European beetle, somewhat resembling Meloë. He states that
Sitaris lays its eggs near the entrance of bees' nests, and at the very
moment that the bee lays her egg in the honey cell, the flattened, ovate
Sitaris larva drops from the body of the bee upon which it has been
living, and feasts upon the contents of the freshly laid egg. After
eating this delicate morsel it devours the honey in the cells of the bee
and changes into a white, cylindrical, nearly footless grub, and after
it is full-fed, and has assumed a supposed "pupa" state, the skin,
without bursting, incloses a kind of hard "pupa" skin, which is very
similar in outline to the former larva, within whose skin is found a
whitish larva which directly changes into the true pupa. In a succeeding
state this pupa in the ordinary way changes to a beetle which belongs to
the same group of Coleoptera as Meloë. We cannot but think, from
observations made on the humble bee, the wasp, two species of moths and
several other insects, that this "hyper-metamorphosis" is not so
abnormal a mode of insect metamorphosis as has been supposed, and that
the changes of these insects, made beneath the skin of the mature larva
before assuming the pupa state, are almost as remarkable as those of
Meloë and Sitaris, though less easily observed than they. Several other
beetles allied to Meloë are known to be parasitic on wild bees, though
the accounts of them are fragmentary.
THE STYLOPS PARASITE.
The history of Stylops, a beetle allied to Meloë, is no less strange
than that of Meloë, and is in some respects still more interesting. On
June 18th I captured an Andrena vicina which had been "stylopized." On
looking at my capture I saw a pale reddish-brown triangular mark on the
bee's abdomen; this was the flattened head and thorax of a female
Stylops (Fig. 39_a_, position of the female of Stylops, seen in profile
in the abdomen of the bee; Fig. 39_b_, the female seen from above. The
head and thorax are soldered into a single flattened mass, the baggy
hind-body being greatly enlarged like that of the gravid female of the
white ant, and consisting of nine segments).
[Illustration: 39. Female Stylops.]
On carefully drawing out the whole body (Pl. 1, Fig. 6, as seen from
above, and showing the alimentary canal ending in a blind sac; Fig.
6_a_, side view), which is very extensible, soft and baggy, and
examining it under a high power of the microscope, we saw multitudes, at
least several hundred, of very minute larvæ, like particles of dust to
the naked eye, issuing in every direction from the body of the parent
now torn open in places, though most of them made their exit through an
opening on the under side of the head-thorax. The Stylops, being hatched
while still in the body of the parent, is, therefore viviparous. She
probably never lays eggs.
On the last of April, when the Mezereon was in blossom, I caught the
singular looking male (Stylops Childreni, Fig. 40; a, side view; it is
about one-fourth of an inch long), which was as unlike its partner as
possible. I laid it under a tumbler, when the delicate insect flew and
tumbled about till it died of exhaustion in a few hours.
It appears, then, that the larvæ are hatched during the middle or last
of June from eggs fertilized in April. The larvæ then crawl out upon the
body of the bee, on which they are transported to the nest, where they
enter, according to Peck's observations, the body of the larva, on whose
fatty parts they feed. Previous to changing to a pupa the larva lives
with its head turned towards that of its host, but before assuming the
perfect state (which they do in the late summer or autumn) it must
reverse its position. The female protrudes the front part of her body
between the segments of the abdomen of her host, as represented in our
figure. This change, Newport thinks, takes place after the bee-host has
undergone its metamorphoses, though the bee does not leave her earthen
cells until the following spring. Though the male Stylops deserts his
host, his wingless partner is imprisoned during her whole life within
her host, and dies immediately after giving birth to her myriad (for
Newport thinks she produces over two thousand) offspring.
[Illustration: 40. Male Stylops.]
Xenos Peckii, an allied insect, was discovered by Dr. Peck to be
parasitic in the body of wasps, and there are now known to be several
species of this small but curious family, Stylopidæ, which are known to
live parasitically on the bodies of our wild bees and wasps. The
presence of these parasites finally exhausts the host, so that the
sterile female bee dies prematurely.
As in the higher animals, bees are afflicted with parasitic worms which
induce disease and sometimes death. The well-known hair worm, Gordius,
is an insect parasite. The adult form is about the size of a slender
knitting needle, and is seen in moist soil and in pools. It lays,
according to Dr. Leidy, "millions of eggs connected together in long
cords." The microscopical, tadpole-shaped young penetrate into the
bodies of insects frequenting damp localities. Fairly ensconced within
the body of their unsuspecting host, they luxuriate on its fatty
tissues, and pass through their metamorphoses into the adult form, when
they desert their living house and take to the water to lay their eggs.
In Europe, Siebold has described Gordius subbifurcus, which infests the
drones of the Honey bee, and also other insects. Professor Siebold has
also described Mermis albicans, which is a similar kind of hair worm,
from two to five inches long, and whitish in color. This worm is also
found, strangely enough, only in the drones, though it is the workers
which frequent watery places to appease their thirst.
[Illustration: 41. Bee fungus.]
Thousands of insects are carried off yearly by parasitic fungi. The
ravages of the Muscardine, caused by a minute fungus (Botrytris
Bassiana), have threatened the extinction of silk culture in Europe, and
the still more formidable disease called _pebrine_ is thought to be of
vegetable origin. Dr. Leidy mentions a fungus which must annually carry
off myriads of the Seventeen Year Locust. A somewhat similar fungus,
Mucor mellitophorus (Fig. 41), infests bees, filling the stomach with
microscopical colorless spores, so as greatly to weaken the insect.
As there is a probability that many insects, parasites on the wild bees,
may sooner or later afflict the Honey bee, and also to illustrate
farther the complex nature of insect parasitism, we will for a moment
look at some other bee parasites.
[Illustration: Pl. 1
PARASITES OF BEES.]
Among the numerous insects preying in some way upon the Humble bee are
to be found other species of bees and moths, flies and beetles. Insect
parasites often imitate their host: Apathus (Plate I, Fig. 1, A.
Ashtoni) can scarcely be distinguished from its host, and yet it lives
cuckoo-like in the cells of the Humble bee, though we know not yet how
injurious it really is. Then there are Conops and Volucella, the
former of which lives like Tachina and Phora within the bee's body,
while the latter devours the brood. The young (Plate I, Figs. 5, 5_a_)
of another fly allied to Anthomyia, of which the Onion fly (Fig. 42) is
an example, is also not unfrequently met with. A small beetle (Plate 1.
Fig. 4, Antherophagus ochraceus) is a common inmate of Humble bees'
nests, and probably feeds upon the wax and pollen. We have also found
several larvæ (Fig. 43) of a beetle of which we do not know the adult
form. Of similar habits is probably a small moth (Nephopteryx Edmandsii,
Plate I, Figs. 2; 2_a_, larva; Fig. 2_b_, chrysalis, or pupa) which
undoubtedly feeds upon the waxen walls of the bee cells, and thus, like
the attacks of the common bee moth (Galleria cereana, whose habits are
so well known as not to detain us, must prove very prejudicial to the
well being of the colony. This moth is in turn infested by an Ichneumon
fly (Microgaster nephoptericis, Plate I, Figs. 3, 3_a_) which must prove
quite destructive.
[Illustration: 42. Onion Fly and Maggot.]
[Illustration: 43. Larva of Beetle.]
The figures of the early stages of a minute ichneumon represented on the
same plate (Fig. 7, larva, and 7_a_, pupa, of Anthophorabia megachilis)
which is parasitic on Megachile, the Leaf-cutter bee, illustrates the
transformations of the Ichneumon flies, the smallest species of which
yet known (and we believe the smallest insect known at all) is the
Pteratomus Putnami (Pl. I, Fig. 8, wanting the hind leg), or "winged
atom," which is only one-ninetieth of an inch in length, and is
parasitic on Anthophorabia, itself a parasite. A species of mite (Plate
I, Figs. 9; 9_a_, the same seen from beneath) is always to be found In
humble bees' nests, but it is not thought to be specially obnoxious to
the bees themselves, though several species of mites (Gamasus, etc.) are
known to be parasitic on insects.