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Bee Flies - Family Bombyliidae
Family Bombyliidae -- bee flies, bombiles
Live adult bee flies photographed in the wild at DuPage County, Illinois, USA.
Bombyliidae larvae are almost all predators of the larval stages of other
insects, primarily bees and wasps in the order
Hymenoptera. |
The large, greenish-yellow bee fly Lepidophora is one "friendly"
fly. On hot summer days, they seem to like to perch on me and bask
in the sun, much like comma butterflies will do. I'm not sure why
they do this. They are not looking for salt or moisture, as do the
commas or
katydids or
tachinid flies
that perch on me and then sample my perspiration. These guys just
sit. They are gorgeous creatures, easily 15mm long.Bombyliidae is
one of the largest families of Diptera, with over 5,000
valid species described worldwide. Their high diversity may
be due to the parasitoid habit of the majority of their
larvae. Adults feed on nectar and pollen, and are believed
to be important pollinators of many plants, although few
species have been studied in detail. Bee flies occur on all
continents except Antarctica, however their highest
diversities occur in semi-arid and arid environments (Hull,
1973).
The family includes a wide variety of morphological forms,
such as the enormous Palirika marginicollis (Gray),
with irridescent green-blue body scales recalling those
found on the wings of a Morpho butterfly, and striking black
and hyaline wings spanning 45 mm; and the tiny, delicate,
humpbacked yellow and black species of Glabellula Bezzi
with hyaline wings and a body length about 1 mm.
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Bee Flies have pubescent (hairy)
bodies and long, slender legs. The proboscis is long,
points forward, and is adapted for feeding on flower
nectar. I most often see Bombylius major
(fig.1) nectaring at dandelion in early spring, a flower
that seemingly does not need such a long proboscis. It
may be that the flowers with long corollas upon which
these flies fed during their long evolution have gone
extinct, or are merely absent from Chicago suburban
environs. Bee flies, like the diurnal clearwing moths
rarely actually come to rest on a flower while feeding.
At most, they dangle their front legs against the bloom,
one assumes for balance and stability. This is probably
in defense against (usually very well-camouflaged)
predators such as crab spiders (family Thomisidae)
and ambush bugs (family Phymatidae) that lie in wait at
flowers.
Eggs are laid near the entrance to
the nest of the specific bee host parasitized by that
species of bee fly. The tiny larvae enter the nest and
usually wait until the bee larva has pupated before
metamorphosing from a small, mobile animal to a smooth,
fat larva which feeds on the bee pupa. The bee fly pupa
is dual-phased. The first pupa is ‘normal’; the second
stage has a sharp battering ram with which to break down
the nest cell wall, made by the adult bee when closing
the cell. |
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Bee Fly, Exoprosopa fascipennis
Photo © Sean McCann
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Figure 1.
Large, forward-looking compound eyes and a long proboscis for
sucking down nectar,
Bombylius major
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Lepidophora lepidocera |
Bombylius major |
Systoechus vulgaris
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Bee flies are stout-bodied flying insects said to resemble long-legged
bumble bees, but I've never seen that connection. There are
Syrphid flies
and
robber flies
that do a much better job of impersonating bumble bees. Many bee
flies have elongated mouthparts that form a conspicuous beak, used
for sucking nectar long-distance while hovering over flowers. Bee
flies much prefer to hover in midair while doing their nectaring,
undoubtedly to avoid capture for those who lurk about flower blooms
looking for an easy meal, such as the
ambush bugs and the
crab spiders. Adult bee
flies become active about the third week in April, here in northern
Illinois. |
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I most often see bee flies hovering around flowers, or if resting,
usually on the ground, on bare soil. They are extremely wary and
difficult to approach. No doubt their large compound eyes give them
good vision, plus they have that air-motion sensing mechanism that
helps the ordinary house fly avoid the swatter. Adult bee flies
drink nectar, but the larvae are parasites of beetle larvae as well
as the brood of solitary wasps and bees, the hole or burrow-nesting
insects. I've often seen female Bombylius sitting in very loose
soil, vibrating her butt like mad, so that the dirt is actually
thrown outwards (see our
Bombylius major pictures).
One source says these flies are "gathering sand to coat their eggs",
ostensibly to keep them from drying out. Uhm.. ok. |
Many bee flies have boldly patterned wings, but it's their shape
that generally tips me off that a specimen is in the Bombyliidae
family. The shape is reminiscent of the best swept-wing fighter
jets. The relatively short and usually pointed antennae are another
clue, along with, of course, that dangerous-looking beak. Good thing
these flies don't bite or sting. All in all, a fascinating insect
worthy of study. Next springtime, why not take a trip to the woods?
You'll find these gals busily gathering nectar from the dandelions
along your favorite sunny path. Just watch out for the dog poo.
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