Regional gardeners are learning to
appreciate native
pollinators, in part due to the activities of National Pollinator Week (the 3rd
week in June). While most people think
of bees when they hear the word ‘pollinator’, in fact a wide range of animals
function as pollinators. To learn more
about pollinators in general see our June 2013 posting (http://mother-natures-backyard.blogspot.com/2013/06/life-friendly-gardening-planning-for.html).
Among
the bee-like insects that serve as pollinators are the Bee Flies. The Family Bombyliidae is a large family of flies with literally hundreds of genera and
thousands of species worldwide. The exact number of species is currently
unknown, due to a significant lack of research on this family. For a good review of the main types of flies seen in Southern California see: http://waynesword.palomar.edu/redmite6.htm
Like the
native bees, Bee Flies range in size from almost microscopic (1 mm/0.05 inches) to large (40 mm/1.5 inches). The evolutionary relationships between
members of this family – and between this and other insect families – are
currently poorly understood. For more
on this topic see: http://en.wikipedia.org/wiki/Bombyliidae
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| Comparison of Bee Fly and Native Bee |
Many
species superficially resemble bees; hence the common name ‘Bee Flies’. Their bodies tend to be compact and dense
(like a bee) with a rounded head; their coloration may also mimic that of bees.
However, Bee Flies differ from bees in
several important ways: 1) a single pair of wings (bees have two pairs) held in
a characteristic, swept back (‘bomber’) position when perched (see above) ; 2)
no stinger; 3) very large, compound eyes (compare above); 4) segmented
antennae; 5) mouths adapted to sucking; 6) long, thin legs (see above).
Bee
Flies usually are black or dark gray in color, sometimes with yellow, gold or
white. Their segmented abdomens (the ‘tail end’ part of the insect) may have
alternating dark and light segments.
They also tend to be hairy; prominent hairs are often visible on head,
thorax (mid-segment) and abdomen (see photo above).
Adult
Bee Flies feed on nectar and (sometimes) pollen. In fact, many have mouth parts adapted for
feeding on a particular species/group of plants (an example of specialization).
Many have a long proboscis (tube-like, sucking mouth part) for sipping nectar. Unlike a butterfly proboscis, which is
slender and uncoils for feeding, the Bee Fly proboscis is stout and rigid. You can often observe it in a good photograph
of a Bee Fly.
Unlike
bees, Bee Flies often don’t actually land when feeding. They hover above the flower, steadying
themselves with their front legs. In
fact, the front legs in some species are notably shorter and more slender than
the other legs - an adaptation to hover-feeding. This hover-feeding behavior may be the first
clue that you’re observing a Bee fly, not a bee.
While
not as specialized as the bees, Bee Fly species are thought to be important
pollinators, particularly in dry climates.
Their frequent visits to flowers and hairy bodies facilitate the
movement of pollen from flower to flower.
They likely function as pollinators in local gardens as well as in the
wild.
The
larvae of Bee Flies are predators or parasites of other insects, often the
larvae or juveniles of ground-dwelling bees and wasps, butterflies/moths, grasshoppers,
beetles, Neuroptera (lacewings, antlions) and other Diptera (flies, gnats, midges). Many Bee Fly larvae
are generalist predators; they feed on several species, depending on
availability. Eggs are often laid in or
near insect burrows, providing the larvae with easy access to food..
While
the larval food aspect can be alarming (particularly for those interested in
conserving the solitary native bees), Bee Flies may actually play an important
role in controlling populations of grasshoppers, beetles and other pest
insects. They are a normal part of the local ecosystem,
helping maintain the balance of plants, insects and other creatures. A functioning, sustainable garden ecosystem should also contain
some Bee Flies, at least in dry areas like Southern California.
A
number of Bee Fly species are known from Southern California, particularly in
the wilds. The best source of photos that we’ve found is Dr. Peter J. Bryant’s
Natural History of Orange County and Nearby Places : http://nathistoc.bio.uci.edu/diptera/Bombyliidae.htm Unfortunately, local Bee Flies are not well-studied; so the number of species
and details of their life history are poorly documented. While this lack of information is lamentable,
it also presents a great opportunity for the observant citizen scientist. In our next posting (July, 2015), we’ll give
some hints on photographing and studying pollinators.
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| Bee Fly (Villa lateralis) on Common yarrow (Achillea millefolia) Mother Nature's Backyard garden, Gardena California |
Villa
lateralis
The
Bee Fly species we see with some regularity in local native plant gardens is Villa lateralis. The genus Villa contains over 250 species, found
on all continents except Antarctica. In
the U.S., most Villa species tend to
be western.
Villa flies have rounded heads, clear or smoky wings with a distinctive,
simple vein pattern, and a ‘chunky’ body with striped abdomen. The genus has not been extensively studied,
and the last North American taxonomic review is over 100 years old [1]. Hence, it may be difficult to key individuals
out to the species level. In fact, the
exact number of Villa species is not
currently known.
The
local Villa lateralis (also known as Anthrax
lateralis var. perimele) is
widely distributed from North America to Panama, including Southern
California. The species has variable
morphology and can be difficult to classify. Individuals from Eastern North
America appear to be distinct from those of the West.
Local
individuals we’ve seen have black bodies with prominent gold-yellow hairs on
the thorax. The abdomen has alternating
stripes of black, yellow-gold and white (see below). If you
look closely you can see the different colored hairs on the stripes. The alternating colored stripes are the most
distinctive feature seen with the naked eye.
 |
| Bee Fly (Villa lateralis) on Common yarrow (Achillea millefolia) Note wing veins and stout proboscis. |
The
wings of Villa lateralis have a
simple, characteristic vein pattern (see above and http://www.drawwing.org/insect/villa-lateralis-wing). The proboscis is stout and not overly long –
about as long as the width of the head.
You can see it in the photograph above, as the insect sips nectar from a
Yarrow flower.
This
species seems to favor plants in the Sunflower family (Asteraceae), at least in local gardens. We’ve observed them most
often in June and July in native plant gardens. We’ve seen them feeding on late-blooming bush
sunflowers (Encelia californica),
common Yarrow (Achillea millefolium),
Goldenrods (Solidago species and Euthamia occidentalis), Telegraph plant
(Heterotheca grandiflora) and Goldenbushes
(Hazardia species). The Natural
History of Orange County and Nearby Places has several photographs of Villa lateralis on Buckwheat (Eriogonum species) and Alkali heliotrope
(Heliotropium curassavicum var. oculatum) flowers; we’ll need to look
for them on these garden flowers as well.
 |
| Bee Fly (Villa lateralis) - Mother Nature's Backyard garden, Gardena California |
In
a study in Oregon [2], Villa lateralis
was found to be a specialist pollinator for several Asteraceae species (Erigeron
foliosus; Eriophyllum lanatum; Haplopappus hallii; Solidago Canadensis).
We
suspect that it may be functioning as a pollinator in local wildlands and
gardens as well. We hope some
enterprising student will study this species in depth sometime soon!
Very little is known about
the larval foods of Villa lateralis in Southern California. The larvae
of several species of Villa
destroy grasshopper eggs; others are parasitic on caterpillars. But almost
nothing has been published about this species in Southern California. If you know someone in search of a research
topic, the life history of Villa lateralis is up for grabs!
For
pictures and more information on this interesting species we recommend:
_________
1.
D.W. Coquillett – Monograph of the species belonging to the genus
Anthrax from America North of Mexico. Transactions of the American Entomological Society and
Proceedings of the Entomological Section of the Academy of Natural Sciences Vol. 14 (1887), pp. 159-182. http://www.jstor.org/stable/25076488
2.
D. Yu - How do the
pollinators' flower preferences affect the features of the pollination network?
http://eco-informatics.engr.oregonstate.edu/previous/2014/Yu_paper.pdf
We encourage your comments below.
If you have questions about Bee Flies or other gardening topics you can
e-mail us at : mothernaturesbackyard10@gmail.com
