Crane flies, belonging to the family Tipulidae, are a diverse group of insects with over 15,500 species and 500 genera described. Often mistaken for large mosquitoes, they are found worldwide and play a significant role in various ecosystems. In colloquial speech, crane flies are known as mosquito hawks or "skeeter-eaters", though they do not actually prey on adult mosquitos or other insects. They are also sometimes called "daddy longlegs", a name which is also used for arachnids of the family Pholcidae and the order Opiliones. Crane flies first appeared during the Middle Triassic, around 245 million years ago, making them one of the oldest known groups of flies, and are found worldwide, though individual species usually have limited ranges.
Physical Characteristics
Tipuloidea are medium to large-sized flies (7-35 mm, 1⁄4-1+1⁄2 in) with elongated legs, wings, and abdomen. Their colour is yellow, brown, or grey. Ocelli are absent. The rostrum (a snout) is short with a beak-like point called the nasus (rarely absent). The apical segment of the maxillary palpi is flagelliform (whip-like) and much longer than the subapical segment. The antennae have 13 segments (exceptionally 14-19). These are whorled, serrate, or ctenidial (comb-like). There is a distinct 'V'‑shaped suture between the mesonotal prescutum and scutum (near the level of the wing bases). The wings are monochromatic, longitudinally striped or marbled. In females the wings are sometimes rudimentary. The sub-costal vein (Sc) joins through Sc2 with the radial vein, Sc1 is at most a short stump. There are four, rarely (when R2 is reduced) three branches of the radial vein merging into the alar margin. The discoidal wing cell is usually present. The wing has two anal veins. Sternite 9 of the male genitalia has, with few exceptions, two pairs of appendages. Sometimes appendages are also present on sternite 8. The female ovipositor has sclerotized valves and the cerci have a smooth or dentate lower margin.
Adult crane flies look like giant mosquitoes. They have slender bodies, very long legs, and one pair of wings that are often held out at a 45-degree angle to the body. Just behind the wings, attached to the body, are two small, antennae-like appendages called halteres. These function like gyroscopes during the crane fly’s weak and wavering flights. The mouthparts look like a snout.
Female crane flies have thicker abdomens, which have a pointed (and harmless) tip for egg-depositing.
Life Cycle
Crane flies undergo complete metamorphosis, with four distinct life stages: egg, larva, pupa, and adult. The life cycle of crane flies directly corresponds with the life cycles of its main food sources. The larvae need fallen tree leaves to feed on, and must therefore mature over the fall and winter. Eggs: A female crane fly lays up to 300 eggs in the ground. Crane fly eggs are black in colour, oval, 1mm long and deposited on the soil surface. The adult female lays her eggs directly in the water or in moist soil. Egg deposition occurs very soon after mating, and the egg stage lasts one to two weeks. The eggs hatch within two weeks of being deposited.
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Larvae: Crane fly larvae (leatherjackets) have been observed in many habitat types on dry land and in water, including marine, brackish, and fresh water. The larvae are cylindrical in shape, but taper toward the front end, and the head capsule is often retracted into the thorax. The abdomen may be smooth, lined with hairs, or studded with projections or welt-like spots. Projections may occur around the spiracles. The larvae are cylindrical, and look like worms, growing up to 4 cm long. The hatched larvae feed on decaying wood, vegetation, and turf, and may cause damage to plant roots in large concentrations. Typically, the crane fly larvae goes through four instars and overwinters under the ground before pupating in mid-to-late spring, just below the soil surface. The larval stage can last anywhere from a few weeks to one year. Longer larval life spans occur if the crane fly overwinters in larval form. When overwintering as larvae, crane flies burrow into moist soil, decaying vegetation, or submerged in the water. Crane fly larvae undergo four stages of development (called instars). They have no legs, appear wormlike, and can be very large; sometimes up to 5 cm! During the final instar, the larvae leave the water to pupate in nearby soil, moss, or leaf litter.
The posterior two-thirds of the head capsule is enclosed or retracted within the prothoracic segment. The larva is metapneustic (with only one pair of spiracles, these on the anal segment of the abdomen), but often with vestigial lateral spiracles (rarely apneustic). The head capsule is sclerotized anteriorly and deeply incised ventrally and often dorsolaterally. The mandibles are opposed and move in the horizontal or oblique plane. The abdominal segments have transverse creeping welts. The terminal segments of the abdomen are glabrous, often partially sclerotized and bearing posterior spiracles.
Pupae: When the adult crane flies emerge, they leave behind pupal cases (puparia) which appear to be small, grey sticks. The crane fly larvae pupate on land, close to the water. During the pupal stage, the body will change, or metamorphose, into the adult form. Once the crane fly has completely undergone metamorphosis, it breaks from the pupal case. Pupae are greyish-brown, and 2.5 cm long. Pupas often have wing sheaths and prominent eyes and may be covered in spines.
Adults: Adults have a lifespan of 10-15 days. The adult female usually contains mature eggs as she emerges from her pupa and often mates immediately if a male is available. Males also search for females by walking or flying. Copulation takes a few minutes to hours and may be accomplished in flight. The female immediately oviposits, usually in wet soil or mats of algae. Some lay eggs on the surface of a water body or in dry soils, and some reportedly simply drop them in flight. Adult common crane flies emerge from the soil in late summer to fall, and females mate and lay 200-300 eggs. On average, crane flies only live in the adult stage for one to three days. During this stage, they’re focused on reproducing. This short lifespan is why many adults don’t even have mouth parts.
Larval Habitats and Diet
Larvae occur in various habitats including marshes, springs, decaying wood, moist soil, leaf litter, fungi, vertebrate nests and vegetation. Larval habitats include all kinds of freshwater, semiaquatic environments. Some Tipuloidea, including Dolichopeza, are found in moist to wet cushions of mosses or liverworts. Ctenophora species are found in decaying wood or sodden logs. Nephrotoma and Tipula larvae are found in dry soils of pasturelands, lawns, and steppe.
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Crane fly larvae have a variety of feeding techniques, which is because they obtain nutrition from a range of different sources. Some species are referred to as 'shredders' because they use well-developed specialized feeding appendages (called mandibles) to shred and feed on algae, bacteria, and diatoms from the surface of rocks, sediments, wood, and other submerged objects. Other species are referred to as 'predators', using their mandibles to kill and consume other living aquatic insects and invertebrates. Still other species are categorized as 'collector/gatherers', and they feed on decomposing organic material, such as bacteria and feces, which have been deposited by animals or water currents. Some species tend to feed on roots and other vegetation, and may cause damage when in large numbers. Larvae may eat algae, microflora, and living or decomposing plant matter, including wood.
Adult Diet
Many species of adult crane fly do not eat at all and don’t even have mouths. They’re alive for such a short time that they don’t need to. Those that do eat only drink nectar from flowers.
Crane Flies as Pests
Some members of the tipulid genus Tipula, such as the European crane fly, Tipula paludosa and the marsh crane fly T. oleracea are agricultural pests in Europe. The larvae of these species live in the top layers of soil where they feed on the roots, root hairs, crown, and sometimes the leaves of crops, stunting their growth or killing the plants. They are pests on a wide variety of plants. Since the late 1900s, T. paludosa and T. oleracea have become invasive in the United States. The larvae have been observed on many crops, including vegetables, fruits, cereals, pasture, lawn grasses, and ornamental plants.
Larval feeding causes brown spots in grasslands, turf and cereal fields. Exit holes of the burrows of the larvae might also be visible.
Control Measures
Registered insecticides can be effective, if used in late fall when eggs are laid and larvae are active. As adult crane flies don’t bite or sting and live extremely short lives, homeowners should focus on eliminating the insects at the larval stage. Several things can be done to prevent crane fly infestations; maintaining a healthy and vibrant turf or lawn will make it less susceptible to the flies. Because crane flies lay eggs in wet soil and the eggs are vulnerable to desiccation, improving drainage to allow proper soil drying and aeration will prevent egg laying. If the eggs are already laid, they will still dry out. There are several registered products available in Canada that can applied as preventive treatment, but always remember to read and follow label instructions of the product. Insect-eating nematodes such as Steinernema species are also registered and available for use as biological control; they feed on the larvae.
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Crane Flies in the Ecosystem
Like many insects that spend their immature stages feeding and growing under water, crane flies grow up, take flight, return to the terrestrial places and become food for land creatures. Adult crane flies may be used for transport by aquatic species of the mite family Ascidae. Crane fly larvae are very important in stream ecosystems. This is because during the process of feeding, they break down fallen leaves into smaller pieces that can then be consumed by smaller organisms. Crane fly species that spend certain stages of their life cycles burrowed in the moist soil serve as prey for land animals such as spiders, centipedes, and predatory beetles. Larvae that inhabit the water are prey for many aquatic animals such as fish, along with some predatory invertebrates such as dragonfly larvae. As adults, crane flies make up an important source of food for spiders, praying mantises, and birds.