Bumble Bee-Mimicking Robber Flies
Robber flies are a special group of predatory flies that possess stout, spiny legs, a dense moustache of bristles on the front of the head (mystax) that protects the robber fly’s head when it encounters struggling or stinging prey, and three simple eyes in a depression between two large compound eyes.
Certain robber flies resemble bumble bees. The evolutionary advantages of a harmless organism mimicking a harmful organism (Batesian mimicry) include deterring predators that are fearful of stinging bees. In addition, it also makes it more likely that a potential prey insect will come closer to the bee mimic, thinking the “bee” is looking for nectar or pollen, not a meaty meal.
A quick way to distinguish a robber fly from a bumble bee is to look at the antennae and wings. Flies usually have short, stubby antennae; bees, including bumble bees, have “elbowed” antennae (an obvious joint). Flies have two wings, while bumble bees (and most other insects) have four. The pointed, stout proboscis, bearded face, fleshy feet and long, tapering abdomen of robber flies are also identifying characteristics. (Photo: Laphria thoracica piercing a click beetle between the beetle’s hardened outer wings (elytra) in order to inject enzymes which will eventually allow the robber fly to drink its prey.)
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Robber Flies Active
You may well have seen a robber fly (also known as an assassin fly) and not recognized it as such. Big eyes, pointed mouthparts, a hairy face and a fondness for insects are robber fly characteristics to look for.
Robber flies are among our largest flies and are predatorial ambushers. They tend to perch for minutes at a time on the tips of leaves, or other sunny viewpoints, where they keep a lookout for unsuspecting prey. Once they spot an insect they lose no time in darting after it. With their beak-like mouthparts they spear the insect and inject a mixture of nerve poisons and enzymes that liquefy the tissues of their victim. They then drink the innards of their prey.
Note that there is a prominent “beard” or tuft of bristles (mystax) in the front of the pictured robber fly’s face. All robber flies have this tuft which serves to protect the face and eyes of the predator from the struggling prey as it dines.
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March Flies Emerging
If you’ve been spending time in fields and meadows recently you may have been witness to the mass emergence of a species of fly known as the March Fly (Bibio albipennis). Their common name is a misnomer, for they are usually seen in April and May in the Northeast. The hatching of March Fly eggs in the soil produces larvae that feed mostly on decaying organic matter. After the larvae pupate and emerge as adults, you find dozens of flies clinging to grass and other vegetation.
Another species of fly in the same genus is known as “Lovebugs,” due to the habit of the males remaining “plugged into” the females during long copulations. Entomologist Stephen Marshall has this to say about their presence in southeastern U.S.: Even though adult Bibionidae are innocuous non-biting insects, the sheer number of fornicating flies fouling car windshields, pitting paint jobs and clogging up radiators renders Lovebugs a well-known Bible Belt nuisance.
The male and female March Fly are sexually dimorphic, differing in appearance. Like many other flies that form male swarms, the males have large heads with massive eyes. The females’ eyes are much smaller. Both are common on flowers and can be significant pollinators of fruit trees.
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Flies Mating
As readers are aware, I spend a significant portion of my time outdoors examining scat, and in so doing, have discovered a family of hairy flies, Heleomyzidae, that are often present on the freshest specimens, especially in early spring and late fall. This spring I have found them mating on both coyote and bear scat. The ardor of males is impressive – without exception the males pounce upon each and every fly of their own species they see. Repeated rejections do not appear to slow them down – just the opposite. In fact, moments after the pictured pair left the surface of a coyote scat and landed on a nearby branch, they were joined by another fly and the threesome tumbled to the ground in an attempt at a menage a trois (see inset).
Different species of flies in this family feed on different food sources. Look for them in and on carcasses, scat, compost, fungi, caves, and bird nests.
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Snow Scorpionflies Active
On mild winter days you may wish to look closely at all the dark, little specks on the surface of the snow. Most of them will be bits of lichen, seeds or pieces of bark, but with luck you may find one or more of them moving. Active winter insects aren’t plentiful, but they do exist.
Scorpionflies are fairly common and can be recognized by their long beaks ending in visible mouthparts. (They get their name from one family of scorpionflies that possesses a scorpion-like tail.) Snow Scorpionflies belong to a family of small, flightless insects, of which there are two species in the Northeast. They only measure about 2/10’s of an inch, so careful scrutiny is necessary to spot one. Their dark color and an anti-freeze substance in their blood allows them to remain active to 21°F., during which time they feed on mosses. When startled, Snow Scorpionflies often jump up in the air and land with their legs crumpled up (see insert) looking even more like an inedible speck of dirt. It’s fairly easy to tell their gender, as female Snow Scorpionflies (photo) lack wings, and males have bristly wings adapted for grasping females.
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Lovebugs Mating
If you see a swarm of small black insects bobbing up and down in the air, you may well be observing the mating ritual of March Flies, also known as Lovebugs. These flies belong to the family Bibionidae, and the majority of species emerge in the spring, hence their common name. (In the Northeast, many appear in April and May.) However, there are certain species which emerge and mate in the fall and they are active now.
March Flies are dimorphic. Males (fly to the left in photo) are easily discernible because of their large eyes, essential for finding mates and chasing competing males. Males comprise most of a swarm, performing an aerial ballet as they bounce up and down, courting females as they emerge from the ground en masse. Once mating has taken place, the male and female of certain species remain attached to one another, even in flight. This is where the name “Lovebug” came from.
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Hover Fly Mimics Bald-faced Hornet
Adult hover flies, often referred to as syrphid (family Syrphidae) or flower flies, feed on pollen and nectar, and are often seen hovering at or crawling on flowers. Many have black and yellow bands on their abdomen, and are frequently mistaken for bees. There are certain species of hover flies that mimic stinging wasps, including yellow jackets and bald-faced hornets (see photo). Predators such as birds, ambush bugs, and spiders might think twice about eating an insect that can sting, and hover flies take advantage of this. The process through which this occurs is called Batesian mimicry, and refers to when a harmless species evolves to imitate a harmful species that has the some of the same predators.
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Robber Fly Mimics Bumblebee
Milkweed leaves make excellent platforms for all kinds of insects, particularly those such as dragonflies and robber flies, which sit, wait and watch, surveying the landscape for prey to ambush. This robber fly could quite easily be mistaken for a bumblebee. However, the short, straight antennae and the presence of only two wings (instead of four) tell you it’s in the order Diptera (true flies). The pointed, stout proboscis, bearded face, fleshy feet and long, tapering abdomen narrow it down to a species of robber fly. Robber flies in the genus Laphria resemble bumblebees – they are typically quite hairy, with black bodies and yellow stripes on their abdomens. Like other species of robber flies, they hunt by perching and snagging prey such as other robber flies, bees, wasps or beetles. They often return to their perch, inject the prey with enzymes that dissolve its innards, and then have a long drink. Why mimic a bumblebee? To deceive unsuspecting honeybees, wasps and other insects that would make a good meal.
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Bloodroot A Fair-weather Friend
Bloodroot (Sanguinaria canadensis), utilizes contrasting white (petals) and yellow (pollen-bearing stamens) colors to attract insects and achieve pollination. The blossoms have no nectar, only pollen, and in order to protect the pollen, the petals of this member of the Poppy family close on overcast days and nights, a time when most pollinators are inactive. The reopening of the flowers depends on temperature and cloud cover. If it’s sunny out, the flowers will open when the temperature reaches 47°F. Native bees, which are Bloodroot’s main pollinators, don’t usually fly until it is 55°F., so flies, capable of flying at slightly lower temperatures, do most of the cool weather pollinating.
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White-tailed Deer Scavengers
According to NPR, each year Americans waste 33 million tons of food (and much of this ends up in landfills where it produces methane, a potent greenhouse gas). This situation is totally alien to that of other animals in the natural world, which seem to find a use for any and every organic particle. Great crested flycatchers incorporate shed snake skins into their nests, beavers build dams and lodges with branches they have eaten the bark off of, ermine line their nests with the fur and feathers of prey — the list goes on and on. When it comes to food, there is equally little waste. The carcasses of animals do not linger long, as almost every atom of their bodies is recycled. Fishers, coyotes, foxes, raccoons, opossums, bald eagles, hawks, woodpeckers, ravens, crows and many other animals make short work of a dead deer in winter. Come spring, if there’s anything left, the final clean-up crew consists of legions of turkey vultures, beetles, flies and bacteria, among others. How unfortunate we’ve strayed so far from a process that’s worked for so many for so long.
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Willow Beaked-Gall Midge
Now that most of the leaves have fallen, it’s a good time to look for galls that form on woody plants. Willows are host to a great number of gall-making insects, including tiny flies called midges. The most common species of willow gall midge is the Willow Beaked-Gall Midge, Rabdophaga rididae. In the spring, after mating, the adult female midge lays an egg in a willow bud (often terminal) that is just starting to expand. The egg soon hatches and the larva burrows deeper into the bud, which causes the bud tissue to swell and form a gall, usually with a “beak” at the top. The larva remains inside the gall through the winter, where it has a constant supply of food (the interior of the gall) and shelter. In the spring the larva pupates, and an adult midge emerges and begins the cycle all over again. Some gall midges are crop pests, but willows are not significantly damaged by the Willow Beaked-Ball Midge.
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Jewelweed Gall Midges
Abnormal plant growths called galls come in all sizes and shapes, are found on leaves, buds and stems, and are caused by a number of agents, including insects. A majority of insect galls are caused by the eggs and developing larvae of flies, wasps and midges. Jewelweed, or Touch-Me-Not (Impatiens capensis), has a very distinctive looking aborted bud gall that is produced by a midge (Schizomyia impatientis). While some galls provide shelter and food for a lone resident, the Jewelweed Gall Midge is colonial, and several orange larvae can be found residing in separate cavities within the gall. These midge larvae are now emerging and will overwinter as adults.
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Clean Antennae Necessary for Sensory Perception
Insect antennae are among the most sensitive and selective chemical-sensing organs in the animal kingdom. They detect information crucial to an insect’s survival, including odors, sounds, humidity, changes in water vapor concentration and air speed. Antennae are capable of these feats because of the sensory receptors covering them which bind to free-floating molecules. Experiments with cockroaches, ants and flies confirm that insects engage in antennal grooming — removing foreign materials from the surface of their antennae with their mandibles — primarily to maintain acute olfactory reception. Pheromones, chemical signals that are vital to insect communication, are used to convey alarm, attract a mate, mark territory and lay out trails, among other things, and clean antennae enhance these messages. (Photo is of a Sword-bearing Conehead Katydid cleaning its antenna.)
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Stinky Squid Fungus
There is no way you can walk by the fruiting body of Pseudocolus fusiformis, a member of the Stinkhorn family Phallaceae, without noticing it. Its shape is markedly different from most fungi, in that it has three or four separate orange “arms” which are fused at the top. If your eyes don’t detect it, your nose most certainly will. Also known as “Stinky Squid,” this fungus emits a strong, putrid odor which comes from the dark green, spore-bearing slimy material (gleba) that is found on the inner surfaces of the arms. This smell attracts insects, primarily flies, which inadvertently disperse spores after visiting the fungus. Look for round egg-like whitish structures at the base of Pseudocolus fusimormis – these are young fruiting bodies that have yet to develop arms. (Thanks to Shiela Swett for photo op.)
Hepatica Blooming
Hepatica has finally opened its hairy buds and greeted the world with its beautiful white, pink, blue and lavender blossoms. Typically the only wildflowers to appear earlier than this member of the Buttercup family are skunk cabbage and coltsfoot. Like many flowers, hepatica blossoms open on sunny days, and close at night and on cloudy days. This prevents rain from washing out the pollen and nectar which help attract pollinating insects, including early-flying bees and flies.
Goldenrod Ball Gall Fly Larva
The round “ball” that is often present on the stem of goldenrod plants contains the overwintering larva of a fly (Eurosta solidaginis). A year ago an adult female fly laid an egg in the stem of the goldenrod plant. The egg hatched and the larva proceeded to eat the interior of the stem. As it did so, the larva excreted chemicals which caused the plant to grow abnormally, creating a ball-shaped “gall.” If you were to open a goldenrod ball gall today, you would probably find an overwintering larva (if a downy woodpecker or parasitic wasp hadn’t gotten there before you). Within the next few weeks the larva will pupate, and as early as April the adult fly will emerge from the gall, having crawled out the passageway that it chewed last fall. An inflatable “balloon” on its forehead allows the fly to burst through the remaining outermost layer of tissue at the end of the passageway. The adult fly lives about two weeks, just long enough to mate and begin the process all over again.
Mating Flies
It’s hard to believe that flies are not only active but mating now, given the snow and low temperatures that Vermont is still experiencing, but these two flies were perched atop coyote scat doing just that. They are in the Heleomyzidae family, whose members are often found in dark or cold places, and are most likely to be encountered in the spring or late fall. There are species associated with caves, mammal burrows, carrion and birds’ nests, in addition to scat.
A Great Christmas Present!
If you’re looking for a present for someone that will be used year round, year after year, Naturally Curious may just fit the bill. A relative, a friend, your child’s school teacher – it’s the gift that keeps on giving to both young and old!
One reader wrote, “This is a unique book as far as I know. I have several naturalists’ books covering Vermont and the Northeast, and have seen nothing of this breadth, covered to this depth. So much interesting information about birds, amphibians, mammals, insects, plants. This would be useful to those in the mid-Atlantic, New York, and even wider geographic regions. The author gives a month-by-month look at what’s going on in the natural world, and so much of the information would simply be moved forward or back a month in other regions, but would still be relevant because of the wide overlap of species. Very readable. Couldn’t put it down. I consider myself pretty knowledgeable about the natural world, but there was much that was new to me in this book. I would have loved to have this to use as a text when I was teaching. Suitable for a wide range of ages.”
In a recent email to me a parent wrote, “Naturally Curious is our five year old’s unqualified f-a-v-o-r-I-t-e book. He spends hours regularly returning to it to study it’s vivid pictures and have us read to him about all the different creatures. It is a ‘must have’ for any family with children living in New England…or for anyone that simply shares a love of the outdoors.”
I am a firm believer in fostering a love of nature in young children – the younger the better — but I admit that when I wrote Naturally Curious, I was writing it with adults in mind. It delights me no end to know that children don’t even need a grown-up middleman to enjoy it!
Pine Cone Willow Gall
Galls are abnormal plant growths that can be caused by insects, fungi, bacteria, nematode worms and mites. Insects cause the greatest number of galls and induce the greatest variety of structures. Galls provide both food and shelter for the organisms living within them. Galls develop during the growing season, often in buds and on leaves. Pine Cone Willow Galls, named for their resemblance to small pine cones, are found on willows, typically in terminal buds. A gall midge (Rhabdophaga strobiloides) is responsible for the willow bud going haywire and developing abnormally. (No-one has determined exactly how insects cause galls, whether it’s the act of laying eggs in or on the plant, or if it’s somehow connected to the chewing of the larvae into the plant.) Each gall-making insect has a specific host plant, or small group of related plant. The galls that each insect species induces and lives in while developing into an adult has a recognizable shape and size. When you think you’re seeing pines cones on willow trees, you’re not hallucinating, you’ve just discovered the temporary home and food supply of a tiny fly, known as a midge.
Botfly Puparium
Congratulations on some very creative guesses! Yesterday’s post was a botfly puparium – a hard case made from an insect’s larval exoskeleton (skin) that covers and protects the pupa. Most insects that go through complete metamorphosis (egg, larva, pupa, adult) don’t have this added protection for their pupal stage, but certain flies, including botflies, do. Botflies are fairly large, hairy flies that resemble bumblebees and are internal parasites of many species of mammals, including humans. Depending on the species, the botfly deposits its eggs on or near the host animal, or on another insect, such as a mosquitoe or housefly, which carries them to their host. The eggs of some species of botflies are ingested or inhaled; those of other species hatch and the larvae bore into their host. After entering and crawling around inside of the host animal for a week or so, most species of botfly larvae settle in a spot just under the host’s skin and remain there for three to ten weeks, consuming the flesh of its host. The lump, or “warble,” that forms just under the host’s skin where the botfly resides increases in size as the larva grows. A tiny hole chewed in the skin allows the larva to breathe, and eventually it exits through this hole. The larva falls to the ground, where it pupates in the soil and later emerges as an adult botfly. (The two yellow bumps at one end of the puparium are spiracles, through which the pupa breathes.) The whole story of this particular puparium is that Jeannie Killam found it in her old farmhouse’s kitchen cupboard, where it probably popped out of a visiting mouse. (Illustration is of a human botfly.)
White-tailed Deer Fawn
White-tailed Deer fawns are close to two months old now, and will retain their spots until their gray winter coat grows in this fall. The dappling of the spots enhances a fawn’s ability to remain camouflaged up until it is large enough and strong enough to outrun most predators. However, it doesn’t hide them from biting insects. During the summer months, when White-tailed Deer, including fawns, have a relatively thin, cool coat of hair, they are very vulnerable to biting insects such as female horse flies and deer flies. These flies make tiny slices with their blade-like mouthparts in their host’s skin in order to have access to their blood. This fawn was being constantly bothered by such flies.
Moose Flies and Moose
My recent quest for finding moose was successful – and my most striking observation, other than their imposing size, was the presence of a multitude of flies on and around the hindquarters of every moose I saw. I assumed they were deer flies, but they didn’t appear to be bothering the moose and research revealed that, in fact, they were moose flies, Haematobosca alcis. These flies can be seen throughout the spring and summer in dense swarms over and on the rumps of moose — five hundred or more may accompany a single moose. Unlike most other biting insects, both male and female moose flies feed on their host’s blood. Although not considered a serious pest (moose tend to pay little attention to them), moose flies may be responsible for sores often found on the hind legs of moose. It is thought that female moose flies may be stimulated by gases released by the moose when it is defecating, after which the female flies descend and deposit eggs into crevices in the moose’s scat.
Snow Flies
It always comes as a surprise to see tiny creatures moving nimbly over the surface of the snow. However, there are quite a few insects and spiders that do, thanks to the glycerol that they produce in their body fluids that keep them from freezing. The Snow Fly (Chionea sp.) is wingless, probably because at sub-freezing temperatures, it would be very hard to generate enough energy for maintaining flight muscles. They (along with other flies, mosquitoes and gnats) do have two vestigial wings called halteres, the little knobs on the fly’s thorax. They inform true flies about the rotation of their body during flight, and are thought to act as sensory organs for the flightless Snow Flies. Throughout most of the year Snow Flies can be found in leaf litter, but come winter the adults emerge, mate and lay up to 200 eggs. The lack of predators such as dragonflies and most insect-eating birds makes winter a relatively safe time for Snow Flies to be out and about. Their life span is about two months, during which time they drink by pressing their proboscis against the snow, but don’t eat. (Snow Fly in photograph is a female, measuring less than ½”.)
Winter Crane Fly
Earlier this week, when temperatures were in the 40’s and the sun was shining in the late afternoon, there were clusters of male winter crane flies (Trichocera sp.) hovering two or three feet above the snow, bobbing up and down as they did their mating dance. Females are on the surface of the snow most of the time, but join a swarm in order to find a mate. Winter crane flies are active throughout the winter, as their name implies, and are a source of food for resident songbirds. The larvae feed on decaying vegetation, and can be found in leaf litter, shelf fungi and compost heaps.
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